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 //===--- Sema.h - Semantic Analysis & AST Building --------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the Sema class, which performs semantic analysis and
 // builds ASTs.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_SEMA_SEMA_H
 #define LLVM_CLANG_SEMA_SEMA_H
 
 #include "clang/APINotes/APINotesManager.h"
 #include "clang/AST/ASTFwd.h"
 #include "clang/AST/ASTLambda.h"
 #include "clang/AST/Attr.h"
 #include "clang/AST/AttrIterator.h"
 #include "clang/AST/CharUnits.h"
 #include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/DeclarationName.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/ExprConcepts.h"
 #include "clang/AST/ExternalASTSource.h"
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/OperationKinds.h"
 #include "clang/AST/StmtCXX.h"
 #include "clang/AST/Type.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/AttrSubjectMatchRules.h"
 #include "clang/Basic/Builtins.h"
 #include "clang/Basic/CapturedStmt.h"
 #include "clang/Basic/Cuda.h"
 #include "clang/Basic/DiagnosticSema.h"
 #include "clang/Basic/ExceptionSpecificationType.h"
 #include "clang/Basic/ExpressionTraits.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/Lambda.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/Module.h"
 #include "clang/Basic/OpenCLOptions.h"
 #include "clang/Basic/OperatorKinds.h"
 #include "clang/Basic/PartialDiagnostic.h"
 #include "clang/Basic/PragmaKinds.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/Specifiers.h"
 #include "clang/Basic/StackExhaustionHandler.h"
 #include "clang/Basic/TemplateKinds.h"
 #include "clang/Basic/TokenKinds.h"
 #include "clang/Basic/TypeTraits.h"
 #include "clang/Sema/AnalysisBasedWarnings.h"
 #include "clang/Sema/Attr.h"
 #include "clang/Sema/CleanupInfo.h"
 #include "clang/Sema/DeclSpec.h"
 #include "clang/Sema/ExternalSemaSource.h"
 #include "clang/Sema/IdentifierResolver.h"
 #include "clang/Sema/Ownership.h"
 #include "clang/Sema/ParsedAttr.h"
 #include "clang/Sema/Redeclaration.h"
 #include "clang/Sema/Scope.h"
 #include "clang/Sema/SemaBase.h"
 #include "clang/Sema/TypoCorrection.h"
 #include "clang/Sema/Weak.h"
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/BitmaskEnum.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/FloatingPointMode.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/STLForwardCompat.h"
 #include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallBitVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/TinyPtrVector.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include <cassert>
 #include <climits>
 #include <cstddef>
 #include <cstdint>
 #include <deque>
 #include <functional>
 #include <iterator>
 #include <memory>
 #include <optional>
 #include <string>
 #include <tuple>
 #include <type_traits>
 #include <utility>
 #include <vector>
 
 namespace llvm {
 struct InlineAsmIdentifierInfo;
 } // namespace llvm
 
 namespace clang {
 class ADLResult;
 class APValue;
 struct ASTConstraintSatisfaction;
 class ASTConsumer;
 class ASTContext;
 class ASTDeclReader;
 class ASTMutationListener;
 class ASTReader;
 class ASTWriter;
 class CXXBasePath;
 class CXXBasePaths;
 class CXXFieldCollector;
 class CodeCompleteConsumer;
 enum class ComparisonCategoryType : unsigned char;
 class ConstraintSatisfaction;
 class DarwinSDKInfo;
 class DeclGroupRef;
 class DeducedTemplateArgument;
 struct DeductionFailureInfo;
 class DependentDiagnostic;
 class Designation;
 class IdentifierInfo;
 class ImplicitConversionSequence;
 typedef MutableArrayRef<ImplicitConversionSequence> ConversionSequenceList;
 class InitializationKind;
 class InitializationSequence;
 class InitializedEntity;
 enum class LangAS : unsigned int;
 class LocalInstantiationScope;
 class LookupResult;
 class MangleNumberingContext;
 typedef ArrayRef<std::pair<IdentifierInfo *, SourceLocation>> ModuleIdPath;
 class ModuleLoader;
 class MultiLevelTemplateArgumentList;
 struct NormalizedConstraint;
 class ObjCInterfaceDecl;
 class ObjCMethodDecl;
 struct OverloadCandidate;
 enum class OverloadCandidateParamOrder : char;
 enum OverloadCandidateRewriteKind : unsigned;
 class OverloadCandidateSet;
 class Preprocessor;
 class SemaAMDGPU;
 class SemaARM;
 class SemaAVR;
 class SemaBPF;
 class SemaCodeCompletion;
 class SemaCUDA;
 class SemaHLSL;
 class SemaHexagon;
 class SemaLoongArch;
 class SemaM68k;
 class SemaMIPS;
 class SemaMSP430;
 class SemaNVPTX;
 class SemaObjC;
 class SemaOpenACC;
 class SemaOpenCL;
 class SemaOpenMP;
 class SemaPPC;
 class SemaPseudoObject;
 class SemaRISCV;
 class SemaSPIRV;
 class SemaSYCL;
 class SemaSwift;
 class SemaSystemZ;
 class SemaWasm;
 class SemaX86;
 class StandardConversionSequence;
 class TemplateArgument;
 class TemplateArgumentLoc;
 class TemplateInstantiationCallback;
 class TemplatePartialOrderingContext;
 class TemplateSpecCandidateSet;
 class Token;
 class TypeConstraint;
 class TypoCorrectionConsumer;
 class UnresolvedSetImpl;
 class UnresolvedSetIterator;
 class VisibleDeclConsumer;
 
 namespace sema {
 class BlockScopeInfo;
 class Capture;
 class CapturedRegionScopeInfo;
 class CapturingScopeInfo;
 class CompoundScopeInfo;
 class DelayedDiagnostic;
 class DelayedDiagnosticPool;
 class FunctionScopeInfo;
 class LambdaScopeInfo;
 class SemaPPCallbacks;
 class TemplateDeductionInfo;
 } // namespace sema
 
 // AssignmentAction - This is used by all the assignment diagnostic functions
 // to represent what is actually causing the operation
 enum class AssignmentAction {
   Assigning,
   Passing,
   Returning,
   Converting,
   Initializing,
   Sending,
   Casting,
   Passing_CFAudited
 };
 inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
                                              const AssignmentAction &AA) {
   DB << llvm::to_underlying(AA);
   return DB;
 }
 
 namespace threadSafety {
 class BeforeSet;
 void threadSafetyCleanup(BeforeSet *Cache);
 } // namespace threadSafety
 
 // FIXME: No way to easily map from TemplateTypeParmTypes to
 // TemplateTypeParmDecls, so we have this horrible PointerUnion.
 typedef std::pair<llvm::PointerUnion<const TemplateTypeParmType *, NamedDecl *>,
                   SourceLocation>
     UnexpandedParameterPack;
 
 /// Describes whether we've seen any nullability information for the given
 /// file.
 struct FileNullability {
   /// The first pointer declarator (of any pointer kind) in the file that does
   /// not have a corresponding nullability annotation.
   SourceLocation PointerLoc;
 
   /// The end location for the first pointer declarator in the file. Used for
   /// placing fix-its.
   SourceLocation PointerEndLoc;
 
   /// Which kind of pointer declarator we saw.
   uint8_t PointerKind;
 
   /// Whether we saw any type nullability annotations in the given file.
   bool SawTypeNullability = false;
 };
 
 /// A mapping from file IDs to a record of whether we've seen nullability
 /// information in that file.
 class FileNullabilityMap {
   /// A mapping from file IDs to the nullability information for each file ID.
   llvm::DenseMap<FileID, FileNullability> Map;
 
   /// A single-element cache based on the file ID.
   struct {
     FileID File;
     FileNullability Nullability;
   } Cache;
 
 public:
   FileNullability &operator[](FileID file) {
     // Check the single-element cache.
     if (file == Cache.File)
       return Cache.Nullability;
 
     // It's not in the single-element cache; flush the cache if we have one.
     if (!Cache.File.isInvalid()) {
       Map[Cache.File] = Cache.Nullability;
     }
 
     // Pull this entry into the cache.
     Cache.File = file;
     Cache.Nullability = Map[file];
     return Cache.Nullability;
   }
 };
 
 /// Tracks expected type during expression parsing, for use in code completion.
 /// The type is tied to a particular token, all functions that update or consume
 /// the type take a start location of the token they are looking at as a
 /// parameter. This avoids updating the type on hot paths in the parser.
 class PreferredTypeBuilder {
 public:
   PreferredTypeBuilder(bool Enabled) : Enabled(Enabled) {}
 
   void enterCondition(Sema &S, SourceLocation Tok);
   void enterReturn(Sema &S, SourceLocation Tok);
   void enterVariableInit(SourceLocation Tok, Decl *D);
   /// Handles e.g. BaseType{ .D = Tok...
   void enterDesignatedInitializer(SourceLocation Tok, QualType BaseType,
                                   const Designation &D);
   /// Computing a type for the function argument may require running
   /// overloading, so we postpone its computation until it is actually needed.
   ///
   /// Clients should be very careful when using this function, as it stores a
   /// function_ref, clients should make sure all calls to get() with the same
   /// location happen while function_ref is alive.
   ///
   /// The callback should also emit signature help as a side-effect, but only
   /// if the completion point has been reached.
   void enterFunctionArgument(SourceLocation Tok,
                              llvm::function_ref<QualType()> ComputeType);
 
   void enterParenExpr(SourceLocation Tok, SourceLocation LParLoc);
   void enterUnary(Sema &S, SourceLocation Tok, tok::TokenKind OpKind,
                   SourceLocation OpLoc);
   void enterBinary(Sema &S, SourceLocation Tok, Expr *LHS, tok::TokenKind Op);
   void enterMemAccess(Sema &S, SourceLocation Tok, Expr *Base);
   void enterSubscript(Sema &S, SourceLocation Tok, Expr *LHS);
   /// Handles all type casts, including C-style cast, C++ casts, etc.
   void enterTypeCast(SourceLocation Tok, QualType CastType);
 
   /// Get the expected type associated with this location, if any.
   ///
   /// If the location is a function argument, determining the expected type
   /// involves considering all function overloads and the arguments so far.
   /// In this case, signature help for these function overloads will be reported
   /// as a side-effect (only if the completion point has been reached).
   QualType get(SourceLocation Tok) const {
     if (!Enabled || Tok != ExpectedLoc)
       return QualType();
     if (!Type.isNull())
       return Type;
     if (ComputeType)
       return ComputeType();
     return QualType();
   }
 
 private:
   bool Enabled;
   /// Start position of a token for which we store expected type.
   SourceLocation ExpectedLoc;
   /// Expected type for a token starting at ExpectedLoc.
   QualType Type;
   /// A function to compute expected type at ExpectedLoc. It is only considered
   /// if Type is null.
   llvm::function_ref<QualType()> ComputeType;
 };
 
 struct SkipBodyInfo {
   SkipBodyInfo() = default;
   bool ShouldSkip = false;
   bool CheckSameAsPrevious = false;
   NamedDecl *Previous = nullptr;
   NamedDecl *New = nullptr;
 };
 
 /// Describes the result of template argument deduction.
 ///
 /// The TemplateDeductionResult enumeration describes the result of
 /// template argument deduction, as returned from
 /// DeduceTemplateArguments(). The separate TemplateDeductionInfo
 /// structure provides additional information about the results of
 /// template argument deduction, e.g., the deduced template argument
 /// list (if successful) or the specific template parameters or
 /// deduced arguments that were involved in the failure.
 enum class TemplateDeductionResult {
   /// Template argument deduction was successful.
   Success = 0,
   /// The declaration was invalid; do nothing.
   Invalid,
   /// Template argument deduction exceeded the maximum template
   /// instantiation depth (which has already been diagnosed).
   InstantiationDepth,
   /// Template argument deduction did not deduce a value
   /// for every template parameter.
   Incomplete,
   /// Template argument deduction did not deduce a value for every
   /// expansion of an expanded template parameter pack.
   IncompletePack,
   /// Template argument deduction produced inconsistent
   /// deduced values for the given template parameter.
   Inconsistent,
   /// Template argument deduction failed due to inconsistent
   /// cv-qualifiers on a template parameter type that would
   /// otherwise be deduced, e.g., we tried to deduce T in "const T"
   /// but were given a non-const "X".
   Underqualified,
   /// Substitution of the deduced template argument values
   /// resulted in an error.
   SubstitutionFailure,
   /// After substituting deduced template arguments, a dependent
   /// parameter type did not match the corresponding argument.
   DeducedMismatch,
   /// After substituting deduced template arguments, an element of
   /// a dependent parameter type did not match the corresponding element
   /// of the corresponding argument (when deducing from an initializer list).
   DeducedMismatchNested,
   /// A non-depnedent component of the parameter did not match the
   /// corresponding component of the argument.
   NonDeducedMismatch,
   /// When performing template argument deduction for a function
   /// template, there were too many call arguments.
   TooManyArguments,
   /// When performing template argument deduction for a function
   /// template, there were too few call arguments.
   TooFewArguments,
   /// The explicitly-specified template arguments were not valid
   /// template arguments for the given template.
   InvalidExplicitArguments,
   /// Checking non-dependent argument conversions failed.
   NonDependentConversionFailure,
   /// The deduced arguments did not satisfy the constraints associated
   /// with the template.
   ConstraintsNotSatisfied,
   /// Deduction failed; that's all we know.
   MiscellaneousDeductionFailure,
   /// CUDA Target attributes do not match.
   CUDATargetMismatch,
   /// Some error which was already diagnosed.
   AlreadyDiagnosed
 };
 
 /// Kinds of C++ special members.
 enum class CXXSpecialMemberKind {
   DefaultConstructor,
   CopyConstructor,
   MoveConstructor,
   CopyAssignment,
   MoveAssignment,
   Destructor,
   Invalid
 };
 
 /// The kind of conversion being performed.
 enum class CheckedConversionKind {
   /// An implicit conversion.
   Implicit,
   /// A C-style cast.
   CStyleCast,
   /// A functional-style cast.
   FunctionalCast,
   /// A cast other than a C-style cast.
   OtherCast,
   /// A conversion for an operand of a builtin overloaded operator.
   ForBuiltinOverloadedOp
 };
 
 enum class TagUseKind {
   Reference,   // Reference to a tag:  'struct foo *X;'
   Declaration, // Fwd decl of a tag:   'struct foo;'
   Definition,  // Definition of a tag: 'struct foo { int X; } Y;'
   Friend       // Friend declaration:  'friend struct foo;'
 };
 
 /// Used with attributes/effects with a boolean condition, e.g. `nonblocking`.
 enum class FunctionEffectMode : uint8_t {
   None,     // effect is not present.
   False,    // effect(false).
   True,     // effect(true).
   Dependent // effect(expr) where expr is dependent.
 };
 
 /// Sema - This implements semantic analysis and AST building for C.
 /// \nosubgrouping
 class Sema final : public SemaBase {
   // Table of Contents
   // -----------------
   // 1. Semantic Analysis (Sema.cpp)
   // 2. API Notes (SemaAPINotes.cpp)
   // 3. C++ Access Control (SemaAccess.cpp)
   // 4. Attributes (SemaAttr.cpp)
   // 5. Availability Attribute Handling (SemaAvailability.cpp)
   // 6. Bounds Safety (SemaBoundsSafety.cpp)
   // 7. Casts (SemaCast.cpp)
   // 8. Extra Semantic Checking (SemaChecking.cpp)
   // 9. C++ Coroutines (SemaCoroutine.cpp)
   // 10. C++ Scope Specifiers (SemaCXXScopeSpec.cpp)
   // 11. Declarations (SemaDecl.cpp)
   // 12. Declaration Attribute Handling (SemaDeclAttr.cpp)
   // 13. C++ Declarations (SemaDeclCXX.cpp)
   // 14. C++ Exception Specifications (SemaExceptionSpec.cpp)
   // 15. Expressions (SemaExpr.cpp)
   // 16. C++ Expressions (SemaExprCXX.cpp)
   // 17. Member Access Expressions (SemaExprMember.cpp)
   // 18. Initializers (SemaInit.cpp)
   // 19. C++ Lambda Expressions (SemaLambda.cpp)
   // 20. Name Lookup (SemaLookup.cpp)
   // 21. Modules (SemaModule.cpp)
   // 22. C++ Overloading (SemaOverload.cpp)
   // 23. Statements (SemaStmt.cpp)
   // 24. `inline asm` Statement (SemaStmtAsm.cpp)
   // 25. Statement Attribute Handling (SemaStmtAttr.cpp)
   // 26. C++ Templates (SemaTemplate.cpp)
   // 27. C++ Template Argument Deduction (SemaTemplateDeduction.cpp)
   // 28. C++ Template Deduction Guide (SemaTemplateDeductionGuide.cpp)
   // 29. C++ Template Instantiation (SemaTemplateInstantiate.cpp)
   // 30. C++ Template Declaration Instantiation
   //     (SemaTemplateInstantiateDecl.cpp)
   // 31. C++ Variadic Templates (SemaTemplateVariadic.cpp)
   // 32. Constraints and Concepts (SemaConcept.cpp)
   // 33. Types (SemaType.cpp)
   // 34. FixIt Helpers (SemaFixItUtils.cpp)
   // 35. Function Effects (SemaFunctionEffects.cpp)
 
   /// \name Semantic Analysis
   /// Implementations are in Sema.cpp
   ///@{
 
 public:
   Sema(Preprocessor &pp, ASTContext &ctxt, ASTConsumer &consumer,
        TranslationUnitKind TUKind = TU_Complete,
        CodeCompleteConsumer *CompletionConsumer = nullptr);
   ~Sema();
 
   /// Perform initialization that occurs after the parser has been
   /// initialized but before it parses anything.
   void Initialize();
 
   /// This virtual key function only exists to limit the emission of debug info
   /// describing the Sema class. GCC and Clang only emit debug info for a class
   /// with a vtable when the vtable is emitted. Sema is final and not
   /// polymorphic, but the debug info size savings are so significant that it is
   /// worth adding a vtable just to take advantage of this optimization.
   virtual void anchor();
 
   const LangOptions &getLangOpts() const { return LangOpts; }
   OpenCLOptions &getOpenCLOptions() { return OpenCLFeatures; }
   FPOptions &getCurFPFeatures() { return CurFPFeatures; }
 
   DiagnosticsEngine &getDiagnostics() const { return Diags; }
   SourceManager &getSourceManager() const { return SourceMgr; }
   Preprocessor &getPreprocessor() const { return PP; }
   ASTContext &getASTContext() const { return Context; }
   ASTConsumer &getASTConsumer() const { return Consumer; }
   ASTMutationListener *getASTMutationListener() const;
   ExternalSemaSource *getExternalSource() const { return ExternalSource.get(); }
 
   DarwinSDKInfo *getDarwinSDKInfoForAvailabilityChecking(SourceLocation Loc,
                                                          StringRef Platform);
   DarwinSDKInfo *getDarwinSDKInfoForAvailabilityChecking();
 
   /// Registers an external source. If an external source already exists,
   ///  creates a multiplex external source and appends to it.
   ///
   ///\param[in] E - A non-null external sema source.
   ///
   void addExternalSource(ExternalSemaSource *E);
 
   /// Print out statistics about the semantic analysis.
   void PrintStats() const;
 
   /// Run some code with "sufficient" stack space. (Currently, at least 256K is
   /// guaranteed). Produces a warning if we're low on stack space and allocates
   /// more in that case. Use this in code that may recurse deeply (for example,
   /// in template instantiation) to avoid stack overflow.
   void runWithSufficientStackSpace(SourceLocation Loc,
                                    llvm::function_ref<void()> Fn);
 
   /// Returns default addr space for method qualifiers.
   LangAS getDefaultCXXMethodAddrSpace() const;
 
   /// Load weak undeclared identifiers from the external source.
   void LoadExternalWeakUndeclaredIdentifiers();
 
   /// Determine if VD, which must be a variable or function, is an external
   /// symbol that nonetheless can't be referenced from outside this translation
   /// unit because its type has no linkage and it's not extern "C".
   bool isExternalWithNoLinkageType(const ValueDecl *VD) const;
 
   /// Obtain a sorted list of functions that are undefined but ODR-used.
   void getUndefinedButUsed(
       SmallVectorImpl<std::pair<NamedDecl *, SourceLocation>> &Undefined);
 
   typedef std::pair<SourceLocation, bool> DeleteExprLoc;
   typedef llvm::SmallVector<DeleteExprLoc, 4> DeleteLocs;
   /// Retrieves list of suspicious delete-expressions that will be checked at
   /// the end of translation unit.
   const llvm::MapVector<FieldDecl *, DeleteLocs> &
   getMismatchingDeleteExpressions() const;
 
   /// Cause the built diagnostic to be emitted on the DiagosticsEngine.
   /// This is closely coupled to the SemaDiagnosticBuilder class and
   /// should not be used elsewhere.
   void EmitDiagnostic(unsigned DiagID, const DiagnosticBuilder &DB);
 
   void addImplicitTypedef(StringRef Name, QualType T);
 
   /// Whether uncompilable error has occurred. This includes error happens
   /// in deferred diagnostics.
   bool hasUncompilableErrorOccurred() const;
 
   /// Looks through the macro-expansion chain for the given
   /// location, looking for a macro expansion with the given name.
   /// If one is found, returns true and sets the location to that
   /// expansion loc.
   bool findMacroSpelling(SourceLocation &loc, StringRef name);
 
   /// Calls \c Lexer::getLocForEndOfToken()
   SourceLocation getLocForEndOfToken(SourceLocation Loc, unsigned Offset = 0);
 
   /// Retrieve the module loader associated with the preprocessor.
   ModuleLoader &getModuleLoader() const;
 
   /// Invent a new identifier for parameters of abbreviated templates.
   IdentifierInfo *
   InventAbbreviatedTemplateParameterTypeName(const IdentifierInfo *ParamName,
                                              unsigned Index);
 
   void emitAndClearUnusedLocalTypedefWarnings();
 
   // Emit all deferred diagnostics.
   void emitDeferredDiags();
 
   enum TUFragmentKind {
     /// The global module fragment, between 'module;' and a module-declaration.
     Global,
     /// A normal translation unit fragment. For a non-module unit, this is the
     /// entire translation unit. Otherwise, it runs from the module-declaration
     /// to the private-module-fragment (if any) or the end of the TU (if not).
     Normal,
     /// The private module fragment, between 'module :private;' and the end of
     /// the translation unit.
     Private
   };
 
   /// This is called before the very first declaration in the translation unit
   /// is parsed. Note that the ASTContext may have already injected some
   /// declarations.
   void ActOnStartOfTranslationUnit();
   /// ActOnEndOfTranslationUnit - This is called at the very end of the
   /// translation unit when EOF is reached and all but the top-level scope is
   /// popped.
   void ActOnEndOfTranslationUnit();
   void ActOnEndOfTranslationUnitFragment(TUFragmentKind Kind);
 
   /// Determines the active Scope associated with the given declaration
   /// context.
   ///
   /// This routine maps a declaration context to the active Scope object that
   /// represents that declaration context in the parser. It is typically used
   /// from "scope-less" code (e.g., template instantiation, lazy creation of
   /// declarations) that injects a name for name-lookup purposes and, therefore,
   /// must update the Scope.
   ///
   /// \returns The scope corresponding to the given declaraion context, or NULL
   /// if no such scope is open.
   Scope *getScopeForContext(DeclContext *Ctx);
 
   void PushFunctionScope();
   void PushBlockScope(Scope *BlockScope, BlockDecl *Block);
   sema::LambdaScopeInfo *PushLambdaScope();
 
   /// This is used to inform Sema what the current TemplateParameterDepth
   /// is during Parsing.  Currently it is used to pass on the depth
   /// when parsing generic lambda 'auto' parameters.
   void RecordParsingTemplateParameterDepth(unsigned Depth);
 
   void PushCapturedRegionScope(Scope *RegionScope, CapturedDecl *CD,
                                RecordDecl *RD, CapturedRegionKind K,
                                unsigned OpenMPCaptureLevel = 0);
 
   /// Custom deleter to allow FunctionScopeInfos to be kept alive for a short
   /// time after they've been popped.
   class PoppedFunctionScopeDeleter {
     Sema *Self;
 
   public:
     explicit PoppedFunctionScopeDeleter(Sema *Self) : Self(Self) {}
     void operator()(sema::FunctionScopeInfo *Scope) const;
   };
 
   using PoppedFunctionScopePtr =
       std::unique_ptr<sema::FunctionScopeInfo, PoppedFunctionScopeDeleter>;
 
   /// Pop a function (or block or lambda or captured region) scope from the
   /// stack.
   ///
   /// \param WP The warning policy to use for CFG-based warnings, or null if
   ///        such warnings should not be produced.
   /// \param D The declaration corresponding to this function scope, if
   ///        producing CFG-based warnings.
   /// \param BlockType The type of the block expression, if D is a BlockDecl.
   PoppedFunctionScopePtr
   PopFunctionScopeInfo(const sema::AnalysisBasedWarnings::Policy *WP = nullptr,
                        const Decl *D = nullptr,
                        QualType BlockType = QualType());
 
   sema::FunctionScopeInfo *getEnclosingFunction() const;
 
   void setFunctionHasBranchIntoScope();
   void setFunctionHasBranchProtectedScope();
   void setFunctionHasIndirectGoto();
   void setFunctionHasMustTail();
 
   void PushCompoundScope(bool IsStmtExpr);
   void PopCompoundScope();
 
   /// Determine whether any errors occurred within this function/method/
   /// block.
   bool hasAnyUnrecoverableErrorsInThisFunction() const;
 
   /// Retrieve the current block, if any.
   sema::BlockScopeInfo *getCurBlock();
 
   /// Get the innermost lambda or block enclosing the current location, if any.
   /// This looks through intervening non-lambda, non-block scopes such as local
   /// functions.
   sema::CapturingScopeInfo *getEnclosingLambdaOrBlock() const;
 
   /// Retrieve the current lambda scope info, if any.
   /// \param IgnoreNonLambdaCapturingScope true if should find the top-most
   /// lambda scope info ignoring all inner capturing scopes that are not
   /// lambda scopes.
   sema::LambdaScopeInfo *
   getCurLambda(bool IgnoreNonLambdaCapturingScope = false);
 
   /// Retrieve the current generic lambda info, if any.
   sema::LambdaScopeInfo *getCurGenericLambda();
 
   /// Retrieve the current captured region, if any.
   sema::CapturedRegionScopeInfo *getCurCapturedRegion();
 
   void ActOnComment(SourceRange Comment);
 
   /// Retrieve the parser's current scope.
   ///
   /// This routine must only be used when it is certain that semantic analysis
   /// and the parser are in precisely the same context, which is not the case
   /// when, e.g., we are performing any kind of template instantiation.
   /// Therefore, the only safe places to use this scope are in the parser
   /// itself and in routines directly invoked from the parser and *never* from
   /// template substitution or instantiation.
   Scope *getCurScope() const { return CurScope; }
 
   IdentifierInfo *getSuperIdentifier() const;
 
   DeclContext *getCurLexicalContext() const {
     return OriginalLexicalContext ? OriginalLexicalContext : CurContext;
   }
 
   SemaDiagnosticBuilder targetDiag(SourceLocation Loc, unsigned DiagID,
                                    const FunctionDecl *FD = nullptr);
   SemaDiagnosticBuilder targetDiag(SourceLocation Loc,
                                    const PartialDiagnostic &PD,
                                    const FunctionDecl *FD = nullptr) {
     return targetDiag(Loc, PD.getDiagID(), FD) << PD;
   }
 
   /// Check if the type is allowed to be used for the current target.
   void checkTypeSupport(QualType Ty, SourceLocation Loc,
                         ValueDecl *D = nullptr);
 
   // /// The kind of conversion being performed.
   // enum CheckedConversionKind {
   //   /// An implicit conversion.
   //   CCK_ImplicitConversion,
   //   /// A C-style cast.
   //   CCK_CStyleCast,
   //   /// A functional-style cast.
   //   CCK_FunctionalCast,
   //   /// A cast other than a C-style cast.
   //   CCK_OtherCast,
   //   /// A conversion for an operand of a builtin overloaded operator.
   //   CCK_ForBuiltinOverloadedOp
   // };
 
   /// ImpCastExprToType - If Expr is not of type 'Type', insert an implicit
   /// cast.  If there is already an implicit cast, merge into the existing one.
   /// If isLvalue, the result of the cast is an lvalue.
   ExprResult ImpCastExprToType(
       Expr *E, QualType Type, CastKind CK, ExprValueKind VK = VK_PRValue,
       const CXXCastPath *BasePath = nullptr,
       CheckedConversionKind CCK = CheckedConversionKind::Implicit);
 
   /// ScalarTypeToBooleanCastKind - Returns the cast kind corresponding
   /// to the conversion from scalar type ScalarTy to the Boolean type.
   static CastKind ScalarTypeToBooleanCastKind(QualType ScalarTy);
 
   /// If \p AllowLambda is true, treat lambda as function.
   DeclContext *getFunctionLevelDeclContext(bool AllowLambda = false) const;
 
   /// Returns a pointer to the innermost enclosing function, or nullptr if the
   /// current context is not inside a function. If \p AllowLambda is true,
   /// this can return the call operator of an enclosing lambda, otherwise
   /// lambdas are skipped when looking for an enclosing function.
   FunctionDecl *getCurFunctionDecl(bool AllowLambda = false) const;
 
   /// getCurMethodDecl - If inside of a method body, this returns a pointer to
   /// the method decl for the method being parsed.  If we're currently
   /// in a 'block', this returns the containing context.
   ObjCMethodDecl *getCurMethodDecl();
 
   /// getCurFunctionOrMethodDecl - Return the Decl for the current ObjC method
   /// or C function we're in, otherwise return null.  If we're currently
   /// in a 'block', this returns the containing context.
   NamedDecl *getCurFunctionOrMethodDecl() const;
 
   /// Warn if we're implicitly casting from a _Nullable pointer type to a
   /// _Nonnull one.
   void diagnoseNullableToNonnullConversion(QualType DstType, QualType SrcType,
                                            SourceLocation Loc);
 
   /// Warn when implicitly casting 0 to nullptr.
   void diagnoseZeroToNullptrConversion(CastKind Kind, const Expr *E);
 
   /// Warn when implicitly changing function effects.
   void diagnoseFunctionEffectConversion(QualType DstType, QualType SrcType,
                                         SourceLocation Loc);
 
   /// makeUnavailableInSystemHeader - There is an error in the current
   /// context.  If we're still in a system header, and we can plausibly
   /// make the relevant declaration unavailable instead of erroring, do
   /// so and return true.
   bool makeUnavailableInSystemHeader(SourceLocation loc,
                                      UnavailableAttr::ImplicitReason reason);
 
   /// Retrieve a suitable printing policy for diagnostics.
   PrintingPolicy getPrintingPolicy() const {
     return getPrintingPolicy(Context, PP);
   }
 
   /// Retrieve a suitable printing policy for diagnostics.
   static PrintingPolicy getPrintingPolicy(const ASTContext &Ctx,
                                           const Preprocessor &PP);
 
   /// Scope actions.
   void ActOnTranslationUnitScope(Scope *S);
 
   /// Determine whether \param D is function like (function or function
   /// template) for parsing.
   bool isDeclaratorFunctionLike(Declarator &D);
 
   /// The maximum alignment, same as in llvm::Value. We duplicate them here
   /// because that allows us not to duplicate the constants in clang code,
   /// which we must to since we can't directly use the llvm constants.
   /// The value is verified against llvm here: lib/CodeGen/CGDecl.cpp
   ///
   /// This is the greatest alignment value supported by load, store, and alloca
   /// instructions, and global values.
   static const unsigned MaxAlignmentExponent = 32;
   static const uint64_t MaximumAlignment = 1ull << MaxAlignmentExponent;
 
   /// Flag indicating whether or not to collect detailed statistics.
   bool CollectStats;
 
   std::unique_ptr<sema::FunctionScopeInfo> CachedFunctionScope;
 
   /// Stack containing information about each of the nested
   /// function, block, and method scopes that are currently active.
   SmallVector<sema::FunctionScopeInfo *, 4> FunctionScopes;
 
   /// The index of the first FunctionScope that corresponds to the current
   /// context.
   unsigned FunctionScopesStart = 0;
 
   /// Track the number of currently active capturing scopes.
   unsigned CapturingFunctionScopes = 0;
 
   llvm::BumpPtrAllocator BumpAlloc;
 
   /// The kind of translation unit we are processing.
   ///
   /// When we're processing a complete translation unit, Sema will perform
   /// end-of-translation-unit semantic tasks (such as creating
   /// initializers for tentative definitions in C) once parsing has
   /// completed. Modules and precompiled headers perform different kinds of
   /// checks.
   const TranslationUnitKind TUKind;
 
   /// Translation Unit Scope - useful to Objective-C actions that need
   /// to lookup file scope declarations in the "ordinary" C decl namespace.
   /// For example, user-defined classes, built-in "id" type, etc.
   Scope *TUScope;
 
   void incrementMSManglingNumber() const {
     return CurScope->incrementMSManglingNumber();
   }
 
   /// Try to recover by turning the given expression into a
   /// call.  Returns true if recovery was attempted or an error was
   /// emitted; this may also leave the ExprResult invalid.
   bool tryToRecoverWithCall(ExprResult &E, const PartialDiagnostic &PD,
                             bool ForceComplain = false,
                             bool (*IsPlausibleResult)(QualType) = nullptr);
 
   /// Figure out if an expression could be turned into a call.
   ///
   /// Use this when trying to recover from an error where the programmer may
   /// have written just the name of a function instead of actually calling it.
   ///
   /// \param E - The expression to examine.
   /// \param ZeroArgCallReturnTy - If the expression can be turned into a call
   ///  with no arguments, this parameter is set to the type returned by such a
   ///  call; otherwise, it is set to an empty QualType.
   /// \param OverloadSet - If the expression is an overloaded function
   ///  name, this parameter is populated with the decls of the various
   ///  overloads.
   bool tryExprAsCall(Expr &E, QualType &ZeroArgCallReturnTy,
                      UnresolvedSetImpl &NonTemplateOverloads);
 
   typedef OpaquePtr<DeclGroupRef> DeclGroupPtrTy;
   typedef OpaquePtr<TemplateName> TemplateTy;
   typedef OpaquePtr<QualType> TypeTy;
 
   OpenCLOptions OpenCLFeatures;
   FPOptions CurFPFeatures;
 
   const LangOptions &LangOpts;
   Preprocessor &PP;
   ASTContext &Context;
   ASTConsumer &Consumer;
   DiagnosticsEngine &Diags;
   SourceManager &SourceMgr;
   api_notes::APINotesManager APINotes;
 
   /// A RAII object to enter scope of a compound statement.
   class CompoundScopeRAII {
   public:
     CompoundScopeRAII(Sema &S, bool IsStmtExpr = false) : S(S) {
       S.ActOnStartOfCompoundStmt(IsStmtExpr);
     }
 
     ~CompoundScopeRAII() { S.ActOnFinishOfCompoundStmt(); }
 
   private:
     Sema &S;
   };
 
   /// An RAII helper that pops function a function scope on exit.
   struct FunctionScopeRAII {
     Sema &S;
     bool Active;
     FunctionScopeRAII(Sema &S) : S(S), Active(true) {}
     ~FunctionScopeRAII() {
       if (Active)
         S.PopFunctionScopeInfo();
     }
     void disable() { Active = false; }
   };
 
   sema::FunctionScopeInfo *getCurFunction() const {
     return FunctionScopes.empty() ? nullptr : FunctionScopes.back();
   }
 
   /// Worker object for performing CFG-based warnings.
   sema::AnalysisBasedWarnings AnalysisWarnings;
   threadSafety::BeforeSet *ThreadSafetyDeclCache;
 
   /// Callback to the parser to parse templated functions when needed.
   typedef void LateTemplateParserCB(void *P, LateParsedTemplate &LPT);
   typedef void LateTemplateParserCleanupCB(void *P);
   LateTemplateParserCB *LateTemplateParser;
   LateTemplateParserCleanupCB *LateTemplateParserCleanup;
   void *OpaqueParser;
 
   void SetLateTemplateParser(LateTemplateParserCB *LTP,
                              LateTemplateParserCleanupCB *LTPCleanup, void *P) {
     LateTemplateParser = LTP;
     LateTemplateParserCleanup = LTPCleanup;
     OpaqueParser = P;
   }
 
   /// Callback to the parser to parse a type expressed as a string.
   std::function<TypeResult(StringRef, StringRef, SourceLocation)>
       ParseTypeFromStringCallback;
 
   /// VAListTagName - The declaration name corresponding to __va_list_tag.
   /// This is used as part of a hack to omit that class from ADL results.
   DeclarationName VAListTagName;
 
   /// Is the last error level diagnostic immediate. This is used to determined
   /// whether the next info diagnostic should be immediate.
   bool IsLastErrorImmediate = true;
 
   class DelayedDiagnostics;
 
   class DelayedDiagnosticsState {
     sema::DelayedDiagnosticPool *SavedPool = nullptr;
     friend class Sema::DelayedDiagnostics;
   };
   typedef DelayedDiagnosticsState ParsingDeclState;
   typedef DelayedDiagnosticsState ProcessingContextState;
 
   /// A class which encapsulates the logic for delaying diagnostics
   /// during parsing and other processing.
   class DelayedDiagnostics {
     /// The current pool of diagnostics into which delayed
     /// diagnostics should go.
     sema::DelayedDiagnosticPool *CurPool = nullptr;
 
   public:
     DelayedDiagnostics() = default;
 
     /// Adds a delayed diagnostic.
     void add(const sema::DelayedDiagnostic &diag); // in DelayedDiagnostic.h
 
     /// Determines whether diagnostics should be delayed.
     bool shouldDelayDiagnostics() { return CurPool != nullptr; }
 
     /// Returns the current delayed-diagnostics pool.
     sema::DelayedDiagnosticPool *getCurrentPool() const { return CurPool; }
 
     /// Enter a new scope.  Access and deprecation diagnostics will be
     /// collected in this pool.
     DelayedDiagnosticsState push(sema::DelayedDiagnosticPool &pool) {
       DelayedDiagnosticsState state;
       state.SavedPool = CurPool;
       CurPool = &pool;
       return state;
     }
 
     /// Leave a delayed-diagnostic state that was previously pushed.
     /// Do not emit any of the diagnostics.  This is performed as part
     /// of the bookkeeping of popping a pool "properly".
     void popWithoutEmitting(DelayedDiagnosticsState state) {
       CurPool = state.SavedPool;
     }
 
     /// Enter a new scope where access and deprecation diagnostics are
     /// not delayed.
     DelayedDiagnosticsState pushUndelayed() {
       DelayedDiagnosticsState state;
       state.SavedPool = CurPool;
       CurPool = nullptr;
       return state;
     }
 
     /// Undo a previous pushUndelayed().
     void popUndelayed(DelayedDiagnosticsState state) {
       assert(CurPool == nullptr);
       CurPool = state.SavedPool;
     }
   } DelayedDiagnostics;
 
   ParsingDeclState PushParsingDeclaration(sema::DelayedDiagnosticPool &pool) {
     return DelayedDiagnostics.push(pool);
   }
 
   /// Diagnostics that are emitted only if we discover that the given function
   /// must be codegen'ed.  Because handling these correctly adds overhead to
   /// compilation, this is currently only enabled for CUDA compilations.
   SemaDiagnosticBuilder::DeferredDiagnosticsType DeviceDeferredDiags;
 
   /// CurContext - This is the current declaration context of parsing.
   DeclContext *CurContext;
 
   SemaAMDGPU &AMDGPU() {
     assert(AMDGPUPtr);
     return *AMDGPUPtr;
   }
 
   SemaARM &ARM() {
     assert(ARMPtr);
     return *ARMPtr;
   }
 
   SemaAVR &AVR() {
     assert(AVRPtr);
     return *AVRPtr;
   }
 
   SemaBPF &BPF() {
     assert(BPFPtr);
     return *BPFPtr;
   }
 
   SemaCodeCompletion &CodeCompletion() {
     assert(CodeCompletionPtr);
     return *CodeCompletionPtr;
   }
 
   SemaCUDA &CUDA() {
     assert(CUDAPtr);
     return *CUDAPtr;
   }
 
   SemaHLSL &HLSL() {
     assert(HLSLPtr);
     return *HLSLPtr;
   }
 
   SemaHexagon &Hexagon() {
     assert(HexagonPtr);
     return *HexagonPtr;
   }
 
   SemaLoongArch &LoongArch() {
     assert(LoongArchPtr);
     return *LoongArchPtr;
   }
 
   SemaM68k &M68k() {
     assert(M68kPtr);
     return *M68kPtr;
   }
 
   SemaMIPS &MIPS() {
     assert(MIPSPtr);
     return *MIPSPtr;
   }
 
   SemaMSP430 &MSP430() {
     assert(MSP430Ptr);
     return *MSP430Ptr;
   }
 
   SemaNVPTX &NVPTX() {
     assert(NVPTXPtr);
     return *NVPTXPtr;
   }
 
   SemaObjC &ObjC() {
     assert(ObjCPtr);
     return *ObjCPtr;
   }
 
   SemaOpenACC &OpenACC() {
     assert(OpenACCPtr);
     return *OpenACCPtr;
   }
 
   SemaOpenCL &OpenCL() {
     assert(OpenCLPtr);
     return *OpenCLPtr;
   }
 
   SemaOpenMP &OpenMP() {
     assert(OpenMPPtr && "SemaOpenMP is dead");
     return *OpenMPPtr;
   }
 
   SemaPPC &PPC() {
     assert(PPCPtr);
     return *PPCPtr;
   }
 
   SemaPseudoObject &PseudoObject() {
     assert(PseudoObjectPtr);
     return *PseudoObjectPtr;
   }
 
   SemaRISCV &RISCV() {
     assert(RISCVPtr);
     return *RISCVPtr;
   }
 
   SemaSPIRV &SPIRV() {
     assert(SPIRVPtr);
     return *SPIRVPtr;
   }
 
   SemaSYCL &SYCL() {
     assert(SYCLPtr);
     return *SYCLPtr;
   }
 
   SemaSwift &Swift() {
     assert(SwiftPtr);
     return *SwiftPtr;
   }
 
   SemaSystemZ &SystemZ() {
     assert(SystemZPtr);
     return *SystemZPtr;
   }
 
   SemaWasm &Wasm() {
     assert(WasmPtr);
     return *WasmPtr;
   }
 
   SemaX86 &X86() {
     assert(X86Ptr);
     return *X86Ptr;
   }
 
   /// Source of additional semantic information.
   IntrusiveRefCntPtr<ExternalSemaSource> ExternalSource;
 
 protected:
   friend class Parser;
   friend class InitializationSequence;
   friend class ASTReader;
   friend class ASTDeclReader;
   friend class ASTWriter;
 
 private:
   std::optional<std::unique_ptr<DarwinSDKInfo>> CachedDarwinSDKInfo;
   bool WarnedDarwinSDKInfoMissing = false;
 
   StackExhaustionHandler StackHandler;
 
   Sema(const Sema &) = delete;
   void operator=(const Sema &) = delete;
 
   /// The handler for the FileChanged preprocessor events.
   ///
   /// Used for diagnostics that implement custom semantic analysis for #include
   /// directives, like -Wpragma-pack.
   sema::SemaPPCallbacks *SemaPPCallbackHandler;
 
   /// The parser's current scope.
   ///
   /// The parser maintains this state here.
   Scope *CurScope;
 
   mutable IdentifierInfo *Ident_super;
 
   std::unique_ptr<SemaAMDGPU> AMDGPUPtr;
   std::unique_ptr<SemaARM> ARMPtr;
   std::unique_ptr<SemaAVR> AVRPtr;
   std::unique_ptr<SemaBPF> BPFPtr;
   std::unique_ptr<SemaCodeCompletion> CodeCompletionPtr;
   std::unique_ptr<SemaCUDA> CUDAPtr;
   std::unique_ptr<SemaHLSL> HLSLPtr;
   std::unique_ptr<SemaHexagon> HexagonPtr;
   std::unique_ptr<SemaLoongArch> LoongArchPtr;
   std::unique_ptr<SemaM68k> M68kPtr;
   std::unique_ptr<SemaMIPS> MIPSPtr;
   std::unique_ptr<SemaMSP430> MSP430Ptr;
   std::unique_ptr<SemaNVPTX> NVPTXPtr;
   std::unique_ptr<SemaObjC> ObjCPtr;
   std::unique_ptr<SemaOpenACC> OpenACCPtr;
   std::unique_ptr<SemaOpenCL> OpenCLPtr;
   std::unique_ptr<SemaOpenMP> OpenMPPtr;
   std::unique_ptr<SemaPPC> PPCPtr;
   std::unique_ptr<SemaPseudoObject> PseudoObjectPtr;
   std::unique_ptr<SemaRISCV> RISCVPtr;
   std::unique_ptr<SemaSPIRV> SPIRVPtr;
   std::unique_ptr<SemaSYCL> SYCLPtr;
   std::unique_ptr<SemaSwift> SwiftPtr;
   std::unique_ptr<SemaSystemZ> SystemZPtr;
   std::unique_ptr<SemaWasm> WasmPtr;
   std::unique_ptr<SemaX86> X86Ptr;
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name API Notes
   /// Implementations are in SemaAPINotes.cpp
   ///@{
 
 public:
   /// Map any API notes provided for this declaration to attributes on the
   /// declaration.
   ///
   /// Triggered by declaration-attribute processing.
   void ProcessAPINotes(Decl *D);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Access Control
   /// Implementations are in SemaAccess.cpp
   ///@{
 
 public:
   enum AccessResult {
     AR_accessible,
     AR_inaccessible,
     AR_dependent,
     AR_delayed
   };
 
   /// SetMemberAccessSpecifier - Set the access specifier of a member.
   /// Returns true on error (when the previous member decl access specifier
   /// is different from the new member decl access specifier).
   bool SetMemberAccessSpecifier(NamedDecl *MemberDecl,
                                 NamedDecl *PrevMemberDecl,
                                 AccessSpecifier LexicalAS);
 
   /// Perform access-control checking on a previously-unresolved member
   /// access which has now been resolved to a member.
   AccessResult CheckUnresolvedMemberAccess(UnresolvedMemberExpr *E,
                                            DeclAccessPair FoundDecl);
   AccessResult CheckUnresolvedLookupAccess(UnresolvedLookupExpr *E,
                                            DeclAccessPair FoundDecl);
 
   /// Checks access to an overloaded operator new or delete.
   AccessResult CheckAllocationAccess(SourceLocation OperatorLoc,
                                      SourceRange PlacementRange,
                                      CXXRecordDecl *NamingClass,
                                      DeclAccessPair FoundDecl,
                                      bool Diagnose = true);
 
   /// Checks access to a constructor.
   AccessResult CheckConstructorAccess(SourceLocation Loc, CXXConstructorDecl *D,
                                       DeclAccessPair FoundDecl,
                                       const InitializedEntity &Entity,
                                       bool IsCopyBindingRefToTemp = false);
 
   /// Checks access to a constructor.
   AccessResult CheckConstructorAccess(SourceLocation Loc, CXXConstructorDecl *D,
                                       DeclAccessPair FoundDecl,
                                       const InitializedEntity &Entity,
                                       const PartialDiagnostic &PDiag);
   AccessResult CheckDestructorAccess(SourceLocation Loc,
                                      CXXDestructorDecl *Dtor,
                                      const PartialDiagnostic &PDiag,
                                      QualType objectType = QualType());
 
   /// Checks access to the target of a friend declaration.
   AccessResult CheckFriendAccess(NamedDecl *D);
 
   /// Checks access to a member.
   AccessResult CheckMemberAccess(SourceLocation UseLoc,
                                  CXXRecordDecl *NamingClass,
                                  DeclAccessPair Found);
 
   /// Checks implicit access to a member in a structured binding.
   AccessResult
   CheckStructuredBindingMemberAccess(SourceLocation UseLoc,
                                      CXXRecordDecl *DecomposedClass,
                                      DeclAccessPair Field);
   AccessResult CheckMemberOperatorAccess(SourceLocation Loc, Expr *ObjectExpr,
                                          const SourceRange &,
                                          DeclAccessPair FoundDecl);
 
   /// Checks access to an overloaded member operator, including
   /// conversion operators.
   AccessResult CheckMemberOperatorAccess(SourceLocation Loc, Expr *ObjectExpr,
                                          Expr *ArgExpr,
                                          DeclAccessPair FoundDecl);
   AccessResult CheckMemberOperatorAccess(SourceLocation Loc, Expr *ObjectExpr,
                                          ArrayRef<Expr *> ArgExprs,
                                          DeclAccessPair FoundDecl);
   AccessResult CheckAddressOfMemberAccess(Expr *OvlExpr,
                                           DeclAccessPair FoundDecl);
 
   /// Checks access for a hierarchy conversion.
   ///
   /// \param ForceCheck true if this check should be performed even if access
   ///     control is disabled;  some things rely on this for semantics
   /// \param ForceUnprivileged true if this check should proceed as if the
   ///     context had no special privileges
   AccessResult CheckBaseClassAccess(SourceLocation AccessLoc, QualType Base,
                                     QualType Derived, const CXXBasePath &Path,
                                     unsigned DiagID, bool ForceCheck = false,
                                     bool ForceUnprivileged = false);
 
   /// Checks access to all the declarations in the given result set.
   void CheckLookupAccess(const LookupResult &R);
 
   /// Checks access to Target from the given class. The check will take access
   /// specifiers into account, but no member access expressions and such.
   ///
   /// \param Target the declaration to check if it can be accessed
   /// \param NamingClass the class in which the lookup was started.
   /// \param BaseType type of the left side of member access expression.
   ///        \p BaseType and \p NamingClass are used for C++ access control.
   ///        Depending on the lookup case, they should be set to the following:
   ///        - lhs.target (member access without a qualifier):
   ///          \p BaseType and \p NamingClass are both the type of 'lhs'.
   ///        - lhs.X::target (member access with a qualifier):
   ///          BaseType is the type of 'lhs', NamingClass is 'X'
   ///        - X::target (qualified lookup without member access):
   ///          BaseType is null, NamingClass is 'X'.
   ///        - target (unqualified lookup).
   ///          BaseType is null, NamingClass is the parent class of 'target'.
   /// \return true if the Target is accessible from the Class, false otherwise.
   bool IsSimplyAccessible(NamedDecl *Decl, CXXRecordDecl *NamingClass,
                           QualType BaseType);
 
   /// Is the given member accessible for the purposes of deciding whether to
   /// define a special member function as deleted?
   bool isMemberAccessibleForDeletion(CXXRecordDecl *NamingClass,
                                      DeclAccessPair Found, QualType ObjectType,
                                      SourceLocation Loc,
                                      const PartialDiagnostic &Diag);
   bool isMemberAccessibleForDeletion(CXXRecordDecl *NamingClass,
                                      DeclAccessPair Found,
                                      QualType ObjectType) {
     return isMemberAccessibleForDeletion(NamingClass, Found, ObjectType,
                                          SourceLocation(), PDiag());
   }
 
   void HandleDependentAccessCheck(
       const DependentDiagnostic &DD,
       const MultiLevelTemplateArgumentList &TemplateArgs);
   void HandleDelayedAccessCheck(sema::DelayedDiagnostic &DD, Decl *Ctx);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Attributes
   /// Implementations are in SemaAttr.cpp
   ///@{
 
 public:
   /// Controls member pointer representation format under the MS ABI.
   LangOptions::PragmaMSPointersToMembersKind
       MSPointerToMemberRepresentationMethod;
 
   bool MSStructPragmaOn; // True when \#pragma ms_struct on
 
   /// Source location for newly created implicit MSInheritanceAttrs
   SourceLocation ImplicitMSInheritanceAttrLoc;
 
   /// pragma clang section kind
   enum PragmaClangSectionKind {
     PCSK_Invalid = 0,
     PCSK_BSS = 1,
     PCSK_Data = 2,
     PCSK_Rodata = 3,
     PCSK_Text = 4,
     PCSK_Relro = 5
   };
 
   enum PragmaClangSectionAction { PCSA_Set = 0, PCSA_Clear = 1 };
 
   struct PragmaClangSection {
     std::string SectionName;
     bool Valid = false;
     SourceLocation PragmaLocation;
   };
 
   PragmaClangSection PragmaClangBSSSection;
   PragmaClangSection PragmaClangDataSection;
   PragmaClangSection PragmaClangRodataSection;
   PragmaClangSection PragmaClangRelroSection;
   PragmaClangSection PragmaClangTextSection;
 
   enum PragmaMsStackAction {
     PSK_Reset = 0x0,                   // #pragma ()
     PSK_Set = 0x1,                     // #pragma (value)
     PSK_Push = 0x2,                    // #pragma (push[, id])
     PSK_Pop = 0x4,                     // #pragma (pop[, id])
     PSK_Show = 0x8,                    // #pragma (show) -- only for "pack"!
     PSK_Push_Set = PSK_Push | PSK_Set, // #pragma (push[, id], value)
     PSK_Pop_Set = PSK_Pop | PSK_Set,   // #pragma (pop[, id], value)
   };
 
   struct PragmaPackInfo {
     PragmaMsStackAction Action;
     StringRef SlotLabel;
     Token Alignment;
   };
 
   // #pragma pack and align.
   class AlignPackInfo {
   public:
     // `Native` represents default align mode, which may vary based on the
     // platform.
     enum Mode : unsigned char { Native, Natural, Packed, Mac68k };
 
     // #pragma pack info constructor
     AlignPackInfo(AlignPackInfo::Mode M, unsigned Num, bool IsXL)
         : PackAttr(true), AlignMode(M), PackNumber(Num), XLStack(IsXL) {
       assert(Num == PackNumber && "The pack number has been truncated.");
     }
 
     // #pragma align info constructor
     AlignPackInfo(AlignPackInfo::Mode M, bool IsXL)
         : PackAttr(false), AlignMode(M),
           PackNumber(M == Packed ? 1 : UninitPackVal), XLStack(IsXL) {}
 
     explicit AlignPackInfo(bool IsXL) : AlignPackInfo(Native, IsXL) {}
 
     AlignPackInfo() : AlignPackInfo(Native, false) {}
 
     // When a AlignPackInfo itself cannot be used, this returns an 32-bit
     // integer encoding for it. This should only be passed to
     // AlignPackInfo::getFromRawEncoding, it should not be inspected directly.
     static uint32_t getRawEncoding(const AlignPackInfo &Info) {
       std::uint32_t Encoding{};
       if (Info.IsXLStack())
         Encoding |= IsXLMask;
 
       Encoding |= static_cast<uint32_t>(Info.getAlignMode()) << 1;
 
       if (Info.IsPackAttr())
         Encoding |= PackAttrMask;
 
       Encoding |= static_cast<uint32_t>(Info.getPackNumber()) << 4;
 
       return Encoding;
     }
 
     static AlignPackInfo getFromRawEncoding(unsigned Encoding) {
       bool IsXL = static_cast<bool>(Encoding & IsXLMask);
       AlignPackInfo::Mode M =
           static_cast<AlignPackInfo::Mode>((Encoding & AlignModeMask) >> 1);
       int PackNumber = (Encoding & PackNumMask) >> 4;
 
       if (Encoding & PackAttrMask)
         return AlignPackInfo(M, PackNumber, IsXL);
 
       return AlignPackInfo(M, IsXL);
     }
 
     bool IsPackAttr() const { return PackAttr; }
 
     bool IsAlignAttr() const { return !PackAttr; }
 
     Mode getAlignMode() const { return AlignMode; }
 
     unsigned getPackNumber() const { return PackNumber; }
 
     bool IsPackSet() const {
       // #pragma align, #pragma pack(), and #pragma pack(0) do not set the pack
       // attriute on a decl.
       return PackNumber != UninitPackVal && PackNumber != 0;
     }
 
     bool IsXLStack() const { return XLStack; }
 
     bool operator==(const AlignPackInfo &Info) const {
       return std::tie(AlignMode, PackNumber, PackAttr, XLStack) ==
              std::tie(Info.AlignMode, Info.PackNumber, Info.PackAttr,
                       Info.XLStack);
     }
 
     bool operator!=(const AlignPackInfo &Info) const {
       return !(*this == Info);
     }
 
   private:
     /// \brief True if this is a pragma pack attribute,
     ///         not a pragma align attribute.
     bool PackAttr;
 
     /// \brief The alignment mode that is in effect.
     Mode AlignMode;
 
     /// \brief The pack number of the stack.
     unsigned char PackNumber;
 
     /// \brief True if it is a XL #pragma align/pack stack.
     bool XLStack;
 
     /// \brief Uninitialized pack value.
     static constexpr unsigned char UninitPackVal = -1;
 
     // Masks to encode and decode an AlignPackInfo.
     static constexpr uint32_t IsXLMask{0x0000'0001};
     static constexpr uint32_t AlignModeMask{0x0000'0006};
     static constexpr uint32_t PackAttrMask{0x00000'0008};
     static constexpr uint32_t PackNumMask{0x0000'01F0};
   };
 
   template <typename ValueType> struct PragmaStack {
     struct Slot {
       llvm::StringRef StackSlotLabel;
       ValueType Value;
       SourceLocation PragmaLocation;
       SourceLocation PragmaPushLocation;
       Slot(llvm::StringRef StackSlotLabel, ValueType Value,
            SourceLocation PragmaLocation, SourceLocation PragmaPushLocation)
           : StackSlotLabel(StackSlotLabel), Value(Value),
             PragmaLocation(PragmaLocation),
             PragmaPushLocation(PragmaPushLocation) {}
     };
 
     void Act(SourceLocation PragmaLocation, PragmaMsStackAction Action,
              llvm::StringRef StackSlotLabel, ValueType Value) {
       if (Action == PSK_Reset) {
         CurrentValue = DefaultValue;
         CurrentPragmaLocation = PragmaLocation;
         return;
       }
       if (Action & PSK_Push)
         Stack.emplace_back(StackSlotLabel, CurrentValue, CurrentPragmaLocation,
                            PragmaLocation);
       else if (Action & PSK_Pop) {
         if (!StackSlotLabel.empty()) {
           // If we've got a label, try to find it and jump there.
           auto I = llvm::find_if(llvm::reverse(Stack), [&](const Slot &x) {
             return x.StackSlotLabel == StackSlotLabel;
           });
           // If we found the label so pop from there.
           if (I != Stack.rend()) {
             CurrentValue = I->Value;
             CurrentPragmaLocation = I->PragmaLocation;
             Stack.erase(std::prev(I.base()), Stack.end());
           }
         } else if (!Stack.empty()) {
           // We do not have a label, just pop the last entry.
           CurrentValue = Stack.back().Value;
           CurrentPragmaLocation = Stack.back().PragmaLocation;
           Stack.pop_back();
         }
       }
       if (Action & PSK_Set) {
         CurrentValue = Value;
         CurrentPragmaLocation = PragmaLocation;
       }
     }
 
     // MSVC seems to add artificial slots to #pragma stacks on entering a C++
     // method body to restore the stacks on exit, so it works like this:
     //
     //   struct S {
     //     #pragma <name>(push, InternalPragmaSlot, <current_pragma_value>)
     //     void Method {}
     //     #pragma <name>(pop, InternalPragmaSlot)
     //   };
     //
     // It works even with #pragma vtordisp, although MSVC doesn't support
     //   #pragma vtordisp(push [, id], n)
     // syntax.
     //
     // Push / pop a named sentinel slot.
     void SentinelAction(PragmaMsStackAction Action, StringRef Label) {
       assert((Action == PSK_Push || Action == PSK_Pop) &&
              "Can only push / pop #pragma stack sentinels!");
       Act(CurrentPragmaLocation, Action, Label, CurrentValue);
     }
 
     // Constructors.
     explicit PragmaStack(const ValueType &Default)
         : DefaultValue(Default), CurrentValue(Default) {}
 
     bool hasValue() const { return CurrentValue != DefaultValue; }
 
     SmallVector<Slot, 2> Stack;
     ValueType DefaultValue; // Value used for PSK_Reset action.
     ValueType CurrentValue;
     SourceLocation CurrentPragmaLocation;
   };
   // FIXME: We should serialize / deserialize these if they occur in a PCH (but
   // we shouldn't do so if they're in a module).
 
   /// Whether to insert vtordisps prior to virtual bases in the Microsoft
   /// C++ ABI.  Possible values are 0, 1, and 2, which mean:
   ///
   /// 0: Suppress all vtordisps
   /// 1: Insert vtordisps in the presence of vbase overrides and non-trivial
   ///    structors
   /// 2: Always insert vtordisps to support RTTI on partially constructed
   ///    objects
   PragmaStack<MSVtorDispMode> VtorDispStack;
   PragmaStack<AlignPackInfo> AlignPackStack;
   // The current #pragma align/pack values and locations at each #include.
   struct AlignPackIncludeState {
     AlignPackInfo CurrentValue;
     SourceLocation CurrentPragmaLocation;
     bool HasNonDefaultValue, ShouldWarnOnInclude;
   };
   SmallVector<AlignPackIncludeState, 8> AlignPackIncludeStack;
   // Segment #pragmas.
   PragmaStack<StringLiteral *> DataSegStack;
   PragmaStack<StringLiteral *> BSSSegStack;
   PragmaStack<StringLiteral *> ConstSegStack;
   PragmaStack<StringLiteral *> CodeSegStack;
 
   // #pragma strict_gs_check.
   PragmaStack<bool> StrictGuardStackCheckStack;
 
   // This stack tracks the current state of Sema.CurFPFeatures.
   PragmaStack<FPOptionsOverride> FpPragmaStack;
   FPOptionsOverride CurFPFeatureOverrides() {
     FPOptionsOverride result;
     if (!FpPragmaStack.hasValue()) {
       result = FPOptionsOverride();
     } else {
       result = FpPragmaStack.CurrentValue;
     }
     return result;
   }
 
   enum PragmaSectionKind {
     PSK_DataSeg,
     PSK_BSSSeg,
     PSK_ConstSeg,
     PSK_CodeSeg,
   };
 
   // RAII object to push / pop sentinel slots for all MS #pragma stacks.
   // Actions should be performed only if we enter / exit a C++ method body.
   class PragmaStackSentinelRAII {
   public:
     PragmaStackSentinelRAII(Sema &S, StringRef SlotLabel, bool ShouldAct);
     ~PragmaStackSentinelRAII();
 
   private:
     Sema &S;
     StringRef SlotLabel;
     bool ShouldAct;
   };
 
   /// Last section used with #pragma init_seg.
   StringLiteral *CurInitSeg;
   SourceLocation CurInitSegLoc;
 
   /// Sections used with #pragma alloc_text.
   llvm::StringMap<std::tuple<StringRef, SourceLocation>> FunctionToSectionMap;
 
   /// VisContext - Manages the stack for \#pragma GCC visibility.
   void *VisContext; // Really a "PragmaVisStack*"
 
   /// This an attribute introduced by \#pragma clang attribute.
   struct PragmaAttributeEntry {
     SourceLocation Loc;
     ParsedAttr *Attribute;
     SmallVector<attr::SubjectMatchRule, 4> MatchRules;
     bool IsUsed;
   };
 
   /// A push'd group of PragmaAttributeEntries.
   struct PragmaAttributeGroup {
     /// The location of the push attribute.
     SourceLocation Loc;
     /// The namespace of this push group.
     const IdentifierInfo *Namespace;
     SmallVector<PragmaAttributeEntry, 2> Entries;
   };
 
   SmallVector<PragmaAttributeGroup, 2> PragmaAttributeStack;
 
   /// The declaration that is currently receiving an attribute from the
   /// #pragma attribute stack.
   const Decl *PragmaAttributeCurrentTargetDecl;
 
   /// This represents the last location of a "#pragma clang optimize off"
   /// directive if such a directive has not been closed by an "on" yet. If
   /// optimizations are currently "on", this is set to an invalid location.
   SourceLocation OptimizeOffPragmaLocation;
 
   /// Get the location for the currently active "\#pragma clang optimize
   /// off". If this location is invalid, then the state of the pragma is "on".
   SourceLocation getOptimizeOffPragmaLocation() const {
     return OptimizeOffPragmaLocation;
   }
 
   /// The "on" or "off" argument passed by \#pragma optimize, that denotes
   /// whether the optimizations in the list passed to the pragma should be
   /// turned off or on. This boolean is true by default because command line
   /// options are honored when `#pragma optimize("", on)`.
   /// (i.e. `ModifyFnAttributeMSPragmaOptimze()` does nothing)
   bool MSPragmaOptimizeIsOn = true;
 
   /// Set of no-builtin functions listed by \#pragma function.
   llvm::SmallSetVector<StringRef, 4> MSFunctionNoBuiltins;
 
   /// AddAlignmentAttributesForRecord - Adds any needed alignment attributes to
   /// a the record decl, to handle '\#pragma pack' and '\#pragma options align'.
   void AddAlignmentAttributesForRecord(RecordDecl *RD);
 
   /// AddMsStructLayoutForRecord - Adds ms_struct layout attribute to record.
   void AddMsStructLayoutForRecord(RecordDecl *RD);
 
   /// Add gsl::Pointer attribute to std::container::iterator
   /// \param ND The declaration that introduces the name
   /// std::container::iterator. \param UnderlyingRecord The record named by ND.
   void inferGslPointerAttribute(NamedDecl *ND, CXXRecordDecl *UnderlyingRecord);
 
   /// Add [[gsl::Owner]] and [[gsl::Pointer]] attributes for std:: types.
   void inferGslOwnerPointerAttribute(CXXRecordDecl *Record);
 
   /// Add [[clang:::lifetimebound]] attr for std:: functions and methods.
   void inferLifetimeBoundAttribute(FunctionDecl *FD);
 
   /// Add [[clang:::lifetime_capture_by(this)]] to STL container methods.
   void inferLifetimeCaptureByAttribute(FunctionDecl *FD);
 
   /// Add [[gsl::Pointer]] attributes for std:: types.
   void inferGslPointerAttribute(TypedefNameDecl *TD);
 
   LifetimeCaptureByAttr *ParseLifetimeCaptureByAttr(const ParsedAttr &AL,
                                                     StringRef ParamName);
   // Processes the argument 'X' in [[clang::lifetime_capture_by(X)]]. Since 'X'
   // can be the name of a function parameter, we need to parse the function
   // declaration and rest of the parameters before processesing 'X'. Therefore
   // do this lazily instead of processing while parsing the annotation itself.
   void LazyProcessLifetimeCaptureByParams(FunctionDecl *FD);
 
   /// Add _Nullable attributes for std:: types.
   void inferNullableClassAttribute(CXXRecordDecl *CRD);
 
   enum PragmaOptionsAlignKind {
     POAK_Native,  // #pragma options align=native
     POAK_Natural, // #pragma options align=natural
     POAK_Packed,  // #pragma options align=packed
     POAK_Power,   // #pragma options align=power
     POAK_Mac68k,  // #pragma options align=mac68k
     POAK_Reset    // #pragma options align=reset
   };
 
   /// ActOnPragmaClangSection - Called on well formed \#pragma clang section
   void ActOnPragmaClangSection(SourceLocation PragmaLoc,
                                PragmaClangSectionAction Action,
                                PragmaClangSectionKind SecKind,
                                StringRef SecName);
 
   /// ActOnPragmaOptionsAlign - Called on well formed \#pragma options align.
   void ActOnPragmaOptionsAlign(PragmaOptionsAlignKind Kind,
                                SourceLocation PragmaLoc);
 
   /// ActOnPragmaPack - Called on well formed \#pragma pack(...).
   void ActOnPragmaPack(SourceLocation PragmaLoc, PragmaMsStackAction Action,
                        StringRef SlotLabel, Expr *Alignment);
 
   /// ConstantFoldAttrArgs - Folds attribute arguments into ConstantExprs
   /// (unless they are value dependent or type dependent). Returns false
   /// and emits a diagnostic if one or more of the arguments could not be
   /// folded into a constant.
   bool ConstantFoldAttrArgs(const AttributeCommonInfo &CI,
                             MutableArrayRef<Expr *> Args);
 
   enum class PragmaAlignPackDiagnoseKind {
     NonDefaultStateAtInclude,
     ChangedStateAtExit
   };
 
   void DiagnoseNonDefaultPragmaAlignPack(PragmaAlignPackDiagnoseKind Kind,
                                          SourceLocation IncludeLoc);
   void DiagnoseUnterminatedPragmaAlignPack();
 
   /// ActOnPragmaMSStruct - Called on well formed \#pragma ms_struct [on|off].
   void ActOnPragmaMSStruct(PragmaMSStructKind Kind);
 
   /// ActOnPragmaMSComment - Called on well formed
   /// \#pragma comment(kind, "arg").
   void ActOnPragmaMSComment(SourceLocation CommentLoc, PragmaMSCommentKind Kind,
                             StringRef Arg);
 
   /// ActOnPragmaDetectMismatch - Call on well-formed \#pragma detect_mismatch
   void ActOnPragmaDetectMismatch(SourceLocation Loc, StringRef Name,
                                  StringRef Value);
 
   /// Are precise floating point semantics currently enabled?
   bool isPreciseFPEnabled() {
     return !CurFPFeatures.getAllowFPReassociate() &&
            !CurFPFeatures.getNoSignedZero() &&
            !CurFPFeatures.getAllowReciprocal() &&
            !CurFPFeatures.getAllowApproxFunc();
   }
 
   void ActOnPragmaFPEvalMethod(SourceLocation Loc,
                                LangOptions::FPEvalMethodKind Value);
 
   /// ActOnPragmaFloatControl - Call on well-formed \#pragma float_control
   void ActOnPragmaFloatControl(SourceLocation Loc, PragmaMsStackAction Action,
                                PragmaFloatControlKind Value);
 
   /// ActOnPragmaMSPointersToMembers - called on well formed \#pragma
   /// pointers_to_members(representation method[, general purpose
   /// representation]).
   void ActOnPragmaMSPointersToMembers(
       LangOptions::PragmaMSPointersToMembersKind Kind,
       SourceLocation PragmaLoc);
 
   /// Called on well formed \#pragma vtordisp().
   void ActOnPragmaMSVtorDisp(PragmaMsStackAction Action,
                              SourceLocation PragmaLoc, MSVtorDispMode Value);
 
   bool UnifySection(StringRef SectionName, int SectionFlags,
                     NamedDecl *TheDecl);
   bool UnifySection(StringRef SectionName, int SectionFlags,
                     SourceLocation PragmaSectionLocation);
 
   /// Called on well formed \#pragma bss_seg/data_seg/const_seg/code_seg.
   void ActOnPragmaMSSeg(SourceLocation PragmaLocation,
                         PragmaMsStackAction Action,
                         llvm::StringRef StackSlotLabel,
                         StringLiteral *SegmentName, llvm::StringRef PragmaName);
 
   /// Called on well formed \#pragma section().
   void ActOnPragmaMSSection(SourceLocation PragmaLocation, int SectionFlags,
                             StringLiteral *SegmentName);
 
   /// Called on well-formed \#pragma init_seg().
   void ActOnPragmaMSInitSeg(SourceLocation PragmaLocation,
                             StringLiteral *SegmentName);
 
   /// Called on well-formed \#pragma alloc_text().
   void ActOnPragmaMSAllocText(
       SourceLocation PragmaLocation, StringRef Section,
       const SmallVector<std::tuple<IdentifierInfo *, SourceLocation>>
           &Functions);
 
   /// ActOnPragmaMSStrictGuardStackCheck - Called on well formed \#pragma
   /// strict_gs_check.
   void ActOnPragmaMSStrictGuardStackCheck(SourceLocation PragmaLocation,
                                           PragmaMsStackAction Action,
                                           bool Value);
 
   /// ActOnPragmaUnused - Called on well-formed '\#pragma unused'.
   void ActOnPragmaUnused(const Token &Identifier, Scope *curScope,
                          SourceLocation PragmaLoc);
 
   void ActOnPragmaAttributeAttribute(ParsedAttr &Attribute,
                                      SourceLocation PragmaLoc,
                                      attr::ParsedSubjectMatchRuleSet Rules);
   void ActOnPragmaAttributeEmptyPush(SourceLocation PragmaLoc,
                                      const IdentifierInfo *Namespace);
 
   /// Called on well-formed '\#pragma clang attribute pop'.
   void ActOnPragmaAttributePop(SourceLocation PragmaLoc,
                                const IdentifierInfo *Namespace);
 
   /// Adds the attributes that have been specified using the
   /// '\#pragma clang attribute push' directives to the given declaration.
   void AddPragmaAttributes(Scope *S, Decl *D);
 
   void PrintPragmaAttributeInstantiationPoint();
 
   void DiagnoseUnterminatedPragmaAttribute();
 
   /// Called on well formed \#pragma clang optimize.
   void ActOnPragmaOptimize(bool On, SourceLocation PragmaLoc);
 
   /// #pragma optimize("[optimization-list]", on | off).
   void ActOnPragmaMSOptimize(SourceLocation Loc, bool IsOn);
 
   /// Call on well formed \#pragma function.
   void
   ActOnPragmaMSFunction(SourceLocation Loc,
                         const llvm::SmallVectorImpl<StringRef> &NoBuiltins);
 
   /// Only called on function definitions; if there is a pragma in scope
   /// with the effect of a range-based optnone, consider marking the function
   /// with attribute optnone.
   void AddRangeBasedOptnone(FunctionDecl *FD);
 
   /// Only called on function definitions; if there is a `#pragma alloc_text`
   /// that decides which code section the function should be in, add
   /// attribute section to the function.
   void AddSectionMSAllocText(FunctionDecl *FD);
 
   /// Adds the 'optnone' attribute to the function declaration if there
   /// are no conflicts; Loc represents the location causing the 'optnone'
   /// attribute to be added (usually because of a pragma).
   void AddOptnoneAttributeIfNoConflicts(FunctionDecl *FD, SourceLocation Loc);
 
   /// Only called on function definitions; if there is a MSVC #pragma optimize
   /// in scope, consider changing the function's attributes based on the
   /// optimization list passed to the pragma.
   void ModifyFnAttributesMSPragmaOptimize(FunctionDecl *FD);
 
   /// Only called on function definitions; if there is a pragma in scope
   /// with the effect of a range-based no_builtin, consider marking the function
   /// with attribute no_builtin.
   void AddImplicitMSFunctionNoBuiltinAttr(FunctionDecl *FD);
 
   /// AddPushedVisibilityAttribute - If '\#pragma GCC visibility' was used,
   /// add an appropriate visibility attribute.
   void AddPushedVisibilityAttribute(Decl *RD);
 
   /// FreeVisContext - Deallocate and null out VisContext.
   void FreeVisContext();
 
   /// ActOnPragmaVisibility - Called on well formed \#pragma GCC visibility... .
   void ActOnPragmaVisibility(const IdentifierInfo *VisType,
                              SourceLocation PragmaLoc);
 
   /// ActOnPragmaFPContract - Called on well formed
   /// \#pragma {STDC,OPENCL} FP_CONTRACT and
   /// \#pragma clang fp contract
   void ActOnPragmaFPContract(SourceLocation Loc, LangOptions::FPModeKind FPC);
 
   /// Called on well formed
   /// \#pragma clang fp reassociate
   /// or
   /// \#pragma clang fp reciprocal
   void ActOnPragmaFPValueChangingOption(SourceLocation Loc, PragmaFPKind Kind,
                                         bool IsEnabled);
 
   /// ActOnPragmaFenvAccess - Called on well formed
   /// \#pragma STDC FENV_ACCESS
   void ActOnPragmaFEnvAccess(SourceLocation Loc, bool IsEnabled);
 
   /// ActOnPragmaCXLimitedRange - Called on well formed
   /// \#pragma STDC CX_LIMITED_RANGE
   void ActOnPragmaCXLimitedRange(SourceLocation Loc,
                                  LangOptions::ComplexRangeKind Range);
 
   /// Called on well formed '\#pragma clang fp' that has option 'exceptions'.
   void ActOnPragmaFPExceptions(SourceLocation Loc,
                                LangOptions::FPExceptionModeKind);
 
   /// Called to set constant rounding mode for floating point operations.
   void ActOnPragmaFEnvRound(SourceLocation Loc, llvm::RoundingMode);
 
   /// Called to set exception behavior for floating point operations.
   void setExceptionMode(SourceLocation Loc, LangOptions::FPExceptionModeKind);
 
   /// PushNamespaceVisibilityAttr - Note that we've entered a
   /// namespace with a visibility attribute.
   void PushNamespaceVisibilityAttr(const VisibilityAttr *Attr,
                                    SourceLocation Loc);
 
   /// PopPragmaVisibility - Pop the top element of the visibility stack; used
   /// for '\#pragma GCC visibility' and visibility attributes on namespaces.
   void PopPragmaVisibility(bool IsNamespaceEnd, SourceLocation EndLoc);
 
   /// Handles semantic checking for features that are common to all attributes,
   /// such as checking whether a parameter was properly specified, or the
   /// correct number of arguments were passed, etc. Returns true if the
   /// attribute has been diagnosed.
   bool checkCommonAttributeFeatures(const Decl *D, const ParsedAttr &A,
                                     bool SkipArgCountCheck = false);
   bool checkCommonAttributeFeatures(const Stmt *S, const ParsedAttr &A,
                                     bool SkipArgCountCheck = false);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Availability Attribute Handling
   /// Implementations are in SemaAvailability.cpp
   ///@{
 
 public:
   /// Issue any -Wunguarded-availability warnings in \c FD
   void DiagnoseUnguardedAvailabilityViolations(Decl *FD);
 
   void handleDelayedAvailabilityCheck(sema::DelayedDiagnostic &DD, Decl *Ctx);
 
   /// Retrieve the current function, if any, that should be analyzed for
   /// potential availability violations.
   sema::FunctionScopeInfo *getCurFunctionAvailabilityContext();
 
   void DiagnoseAvailabilityOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
                                   const ObjCInterfaceDecl *UnknownObjCClass,
                                   bool ObjCPropertyAccess,
                                   bool AvoidPartialAvailabilityChecks = false,
                                   ObjCInterfaceDecl *ClassReceiver = nullptr);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Bounds Safety
   /// Implementations are in SemaBoundsSafety.cpp
   ///@{
 public:
   /// Check if applying the specified attribute variant from the "counted by"
   /// family of attributes to FieldDecl \p FD is semantically valid. If
   /// semantically invalid diagnostics will be emitted explaining the problems.
   ///
   /// \param FD The FieldDecl to apply the attribute to
   /// \param E The count expression on the attribute
   /// \param CountInBytes If true the attribute is from the "sized_by" family of
   ///                     attributes. If the false the attribute is from
   ///                     "counted_by" family of attributes.
   /// \param OrNull If true the attribute is from the "_or_null" suffixed family
   ///               of attributes. If false the attribute does not have the
   ///               suffix.
   ///
   /// Together \p CountInBytes and \p OrNull decide the attribute variant. E.g.
   /// \p CountInBytes and \p OrNull both being true indicates the
   /// `counted_by_or_null` attribute.
   ///
   /// \returns false iff semantically valid.
   bool CheckCountedByAttrOnField(FieldDecl *FD, Expr *E, bool CountInBytes,
                                  bool OrNull);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Casts
   /// Implementations are in SemaCast.cpp
   ///@{
 
 public:
   static bool isCast(CheckedConversionKind CCK) {
     return CCK == CheckedConversionKind::CStyleCast ||
            CCK == CheckedConversionKind::FunctionalCast ||
            CCK == CheckedConversionKind::OtherCast;
   }
 
   /// ActOnCXXNamedCast - Parse
   /// {dynamic,static,reinterpret,const,addrspace}_cast's.
   ExprResult ActOnCXXNamedCast(SourceLocation OpLoc, tok::TokenKind Kind,
                                SourceLocation LAngleBracketLoc, Declarator &D,
                                SourceLocation RAngleBracketLoc,
                                SourceLocation LParenLoc, Expr *E,
                                SourceLocation RParenLoc);
 
   ExprResult BuildCXXNamedCast(SourceLocation OpLoc, tok::TokenKind Kind,
                                TypeSourceInfo *Ty, Expr *E,
                                SourceRange AngleBrackets, SourceRange Parens);
 
   ExprResult ActOnBuiltinBitCastExpr(SourceLocation KWLoc, Declarator &Dcl,
                                      ExprResult Operand,
                                      SourceLocation RParenLoc);
 
   ExprResult BuildBuiltinBitCastExpr(SourceLocation KWLoc, TypeSourceInfo *TSI,
                                      Expr *Operand, SourceLocation RParenLoc);
 
   // Checks that reinterpret casts don't have undefined behavior.
   void CheckCompatibleReinterpretCast(QualType SrcType, QualType DestType,
                                       bool IsDereference, SourceRange Range);
 
   // Checks that the vector type should be initialized from a scalar
   // by splatting the value rather than populating a single element.
   // This is the case for AltiVecVector types as well as with
   // AltiVecPixel and AltiVecBool when -faltivec-src-compat=xl is specified.
   bool ShouldSplatAltivecScalarInCast(const VectorType *VecTy);
 
   // Checks if the -faltivec-src-compat=gcc option is specified.
   // If so, AltiVecVector, AltiVecBool and AltiVecPixel types are
   // treated the same way as they are when trying to initialize
   // these vectors on gcc (an error is emitted).
   bool CheckAltivecInitFromScalar(SourceRange R, QualType VecTy,
                                   QualType SrcTy);
 
   ExprResult BuildCStyleCastExpr(SourceLocation LParenLoc, TypeSourceInfo *Ty,
                                  SourceLocation RParenLoc, Expr *Op);
 
   ExprResult BuildCXXFunctionalCastExpr(TypeSourceInfo *TInfo, QualType Type,
                                         SourceLocation LParenLoc,
                                         Expr *CastExpr,
                                         SourceLocation RParenLoc);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Extra Semantic Checking
   /// Implementations are in SemaChecking.cpp
   ///@{
 
 public:
   /// Used to change context to isConstantEvaluated without pushing a heavy
   /// ExpressionEvaluationContextRecord object.
   bool isConstantEvaluatedOverride = false;
 
   bool isConstantEvaluatedContext() const {
     return currentEvaluationContext().isConstantEvaluated() ||
            isConstantEvaluatedOverride;
   }
 
   SourceLocation getLocationOfStringLiteralByte(const StringLiteral *SL,
                                                 unsigned ByteNo) const;
 
   enum FormatArgumentPassingKind {
     FAPK_Fixed,    // values to format are fixed (no C-style variadic arguments)
     FAPK_Variadic, // values to format are passed as variadic arguments
     FAPK_VAList,   // values to format are passed in a va_list
   };
 
   // Used to grab the relevant information from a FormatAttr and a
   // FunctionDeclaration.
   struct FormatStringInfo {
     unsigned FormatIdx;
     unsigned FirstDataArg;
     FormatArgumentPassingKind ArgPassingKind;
   };
 
   /// Given a FunctionDecl's FormatAttr, attempts to populate the
   /// FomatStringInfo parameter with the FormatAttr's correct format_idx and
   /// firstDataArg. Returns true when the format fits the function and the
   /// FormatStringInfo has been populated.
   static bool getFormatStringInfo(const FormatAttr *Format, bool IsCXXMember,
                                   bool IsVariadic, FormatStringInfo *FSI);
 
   // Used by C++ template instantiation.
   ExprResult BuiltinShuffleVector(CallExpr *TheCall);
 
   /// ConvertVectorExpr - Handle __builtin_convertvector
   ExprResult ConvertVectorExpr(Expr *E, TypeSourceInfo *TInfo,
                                SourceLocation BuiltinLoc,
                                SourceLocation RParenLoc);
 
   enum FormatStringType {
     FST_Scanf,
     FST_Printf,
     FST_NSString,
     FST_Strftime,
     FST_Strfmon,
     FST_Kprintf,
     FST_FreeBSDKPrintf,
     FST_OSTrace,
     FST_OSLog,
     FST_Syslog,
     FST_Unknown
   };
   static FormatStringType GetFormatStringType(const FormatAttr *Format);
 
   bool FormatStringHasSArg(const StringLiteral *FExpr);
 
   /// Check for comparisons of floating-point values using == and !=. Issue a
   /// warning if the comparison is not likely to do what the programmer
   /// intended.
   void CheckFloatComparison(SourceLocation Loc, Expr *LHS, Expr *RHS,
                             BinaryOperatorKind Opcode);
 
   /// Register a magic integral constant to be used as a type tag.
   void RegisterTypeTagForDatatype(const IdentifierInfo *ArgumentKind,
                                   uint64_t MagicValue, QualType Type,
                                   bool LayoutCompatible, bool MustBeNull);
 
   struct TypeTagData {
     TypeTagData() {}
 
     TypeTagData(QualType Type, bool LayoutCompatible, bool MustBeNull)
         : Type(Type), LayoutCompatible(LayoutCompatible),
           MustBeNull(MustBeNull) {}
 
     QualType Type;
 
     /// If true, \c Type should be compared with other expression's types for
     /// layout-compatibility.
     LLVM_PREFERRED_TYPE(bool)
     unsigned LayoutCompatible : 1;
     LLVM_PREFERRED_TYPE(bool)
     unsigned MustBeNull : 1;
   };
 
   /// A pair of ArgumentKind identifier and magic value.  This uniquely
   /// identifies the magic value.
   typedef std::pair<const IdentifierInfo *, uint64_t> TypeTagMagicValue;
 
   /// Diagnoses the current set of gathered accesses. This typically
   /// happens at full expression level. The set is cleared after emitting the
   /// diagnostics.
   void DiagnoseMisalignedMembers();
 
   /// This function checks if the expression is in the sef of potentially
   /// misaligned members and it is converted to some pointer type T with lower
   /// or equal alignment requirements. If so it removes it. This is used when
   /// we do not want to diagnose such misaligned access (e.g. in conversions to
   /// void*).
   void DiscardMisalignedMemberAddress(const Type *T, Expr *E);
 
   /// This function calls Action when it determines that E designates a
   /// misaligned member due to the packed attribute. This is used to emit
   /// local diagnostics like in reference binding.
   void RefersToMemberWithReducedAlignment(
       Expr *E,
       llvm::function_ref<void(Expr *, RecordDecl *, FieldDecl *, CharUnits)>
           Action);
 
   enum class AtomicArgumentOrder { API, AST };
   ExprResult
   BuildAtomicExpr(SourceRange CallRange, SourceRange ExprRange,
                   SourceLocation RParenLoc, MultiExprArg Args,
                   AtomicExpr::AtomicOp Op,
                   AtomicArgumentOrder ArgOrder = AtomicArgumentOrder::API);
 
   /// Check to see if a given expression could have '.c_str()' called on it.
   bool hasCStrMethod(const Expr *E);
 
   /// Diagnose pointers that are always non-null.
   /// \param E the expression containing the pointer
   /// \param NullKind NPCK_NotNull if E is a cast to bool, otherwise, E is
   /// compared to a null pointer
   /// \param IsEqual True when the comparison is equal to a null pointer
   /// \param Range Extra SourceRange to highlight in the diagnostic
   void DiagnoseAlwaysNonNullPointer(Expr *E,
                                     Expr::NullPointerConstantKind NullType,
                                     bool IsEqual, SourceRange Range);
 
   /// CheckParmsForFunctionDef - Check that the parameters of the given
   /// function are appropriate for the definition of a function. This
   /// takes care of any checks that cannot be performed on the
   /// declaration itself, e.g., that the types of each of the function
   /// parameters are complete.
   bool CheckParmsForFunctionDef(ArrayRef<ParmVarDecl *> Parameters,
                                 bool CheckParameterNames);
 
   /// CheckCastAlign - Implements -Wcast-align, which warns when a
   /// pointer cast increases the alignment requirements.
   void CheckCastAlign(Expr *Op, QualType T, SourceRange TRange);
 
   /// checkUnsafeAssigns - Check whether +1 expr is being assigned
   /// to weak/__unsafe_unretained type.
   bool checkUnsafeAssigns(SourceLocation Loc, QualType LHS, Expr *RHS);
 
   /// checkUnsafeExprAssigns - Check whether +1 expr is being assigned
   /// to weak/__unsafe_unretained expression.
   void checkUnsafeExprAssigns(SourceLocation Loc, Expr *LHS, Expr *RHS);
 
   /// Emit \p DiagID if statement located on \p StmtLoc has a suspicious null
   /// statement as a \p Body, and it is located on the same line.
   ///
   /// This helps prevent bugs due to typos, such as:
   ///     if (condition);
   ///       do_stuff();
   void DiagnoseEmptyStmtBody(SourceLocation StmtLoc, const Stmt *Body,
                              unsigned DiagID);
 
   /// Warn if a for/while loop statement \p S, which is followed by
   /// \p PossibleBody, has a suspicious null statement as a body.
   void DiagnoseEmptyLoopBody(const Stmt *S, const Stmt *PossibleBody);
 
   /// DiagnoseSelfMove - Emits a warning if a value is moved to itself.
   void DiagnoseSelfMove(const Expr *LHSExpr, const Expr *RHSExpr,
                         SourceLocation OpLoc);
 
   // Used for emitting the right warning by DefaultVariadicArgumentPromotion
   enum VariadicCallType {
     VariadicFunction,
     VariadicBlock,
     VariadicMethod,
     VariadicConstructor,
     VariadicDoesNotApply
   };
 
   bool IsLayoutCompatible(QualType T1, QualType T2) const;
   bool IsPointerInterconvertibleBaseOf(const TypeSourceInfo *Base,
                                        const TypeSourceInfo *Derived);
 
   /// CheckFunctionCall - Check a direct function call for various correctness
   /// and safety properties not strictly enforced by the C type system.
   bool CheckFunctionCall(FunctionDecl *FDecl, CallExpr *TheCall,
                          const FunctionProtoType *Proto);
 
   /// \param FPOnly restricts the arguments to floating-point types.
   bool BuiltinVectorMath(CallExpr *TheCall, QualType &Res, bool FPOnly = false);
   bool BuiltinVectorToScalarMath(CallExpr *TheCall);
 
   void checkLifetimeCaptureBy(FunctionDecl *FDecl, bool IsMemberFunction,
                               const Expr *ThisArg, ArrayRef<const Expr *> Args);
 
   /// Handles the checks for format strings, non-POD arguments to vararg
   /// functions, NULL arguments passed to non-NULL parameters, diagnose_if
   /// attributes and AArch64 SME attributes.
   void checkCall(NamedDecl *FDecl, const FunctionProtoType *Proto,
                  const Expr *ThisArg, ArrayRef<const Expr *> Args,
                  bool IsMemberFunction, SourceLocation Loc, SourceRange Range,
                  VariadicCallType CallType);
 
   /// \brief Enforce the bounds of a TCB
   /// CheckTCBEnforcement - Enforces that every function in a named TCB only
   /// directly calls other functions in the same TCB as marked by the
   /// enforce_tcb and enforce_tcb_leaf attributes.
   void CheckTCBEnforcement(const SourceLocation CallExprLoc,
                            const NamedDecl *Callee);
 
   void CheckConstrainedAuto(const AutoType *AutoT, SourceLocation Loc);
 
   /// BuiltinConstantArg - Handle a check if argument ArgNum of CallExpr
   /// TheCall is a constant expression.
   bool BuiltinConstantArg(CallExpr *TheCall, int ArgNum, llvm::APSInt &Result);
 
   /// BuiltinConstantArgRange - Handle a check if argument ArgNum of CallExpr
   /// TheCall is a constant expression in the range [Low, High].
   bool BuiltinConstantArgRange(CallExpr *TheCall, int ArgNum, int Low, int High,
                                bool RangeIsError = true);
 
   /// BuiltinConstantArgMultiple - Handle a check if argument ArgNum of CallExpr
   /// TheCall is a constant expression is a multiple of Num..
   bool BuiltinConstantArgMultiple(CallExpr *TheCall, int ArgNum,
                                   unsigned Multiple);
 
   /// BuiltinConstantArgPower2 - Check if argument ArgNum of TheCall is a
   /// constant expression representing a power of 2.
   bool BuiltinConstantArgPower2(CallExpr *TheCall, int ArgNum);
 
   /// BuiltinConstantArgShiftedByte - Check if argument ArgNum of TheCall is
   /// a constant expression representing an arbitrary byte value shifted left by
   /// a multiple of 8 bits.
   bool BuiltinConstantArgShiftedByte(CallExpr *TheCall, int ArgNum,
                                      unsigned ArgBits);
 
   /// BuiltinConstantArgShiftedByteOr0xFF - Check if argument ArgNum of
   /// TheCall is a constant expression representing either a shifted byte value,
   /// or a value of the form 0x??FF (i.e. a member of the arithmetic progression
   /// 0x00FF, 0x01FF, ..., 0xFFFF). This strange range check is needed for some
   /// Arm MVE intrinsics.
   bool BuiltinConstantArgShiftedByteOrXXFF(CallExpr *TheCall, int ArgNum,
                                            unsigned ArgBits);
 
   /// Checks that a call expression's argument count is at least the desired
   /// number. This is useful when doing custom type-checking on a variadic
   /// function. Returns true on error.
   bool checkArgCountAtLeast(CallExpr *Call, unsigned MinArgCount);
 
   /// Checks that a call expression's argument count is at most the desired
   /// number. This is useful when doing custom type-checking on a variadic
   /// function. Returns true on error.
   bool checkArgCountAtMost(CallExpr *Call, unsigned MaxArgCount);
 
   /// Checks that a call expression's argument count is in the desired range.
   /// This is useful when doing custom type-checking on a variadic function.
   /// Returns true on error.
   bool checkArgCountRange(CallExpr *Call, unsigned MinArgCount,
                           unsigned MaxArgCount);
 
   /// Checks that a call expression's argument count is the desired number.
   /// This is useful when doing custom type-checking.  Returns true on error.
   bool checkArgCount(CallExpr *Call, unsigned DesiredArgCount);
 
   /// Returns true if the argument consists of one contiguous run of 1s with any
   /// number of 0s on either side. The 1s are allowed to wrap from LSB to MSB,
   /// so 0x000FFF0, 0x0000FFFF, 0xFF0000FF, 0x0 are all runs. 0x0F0F0000 is not,
   /// since all 1s are not contiguous.
   bool ValueIsRunOfOnes(CallExpr *TheCall, unsigned ArgNum);
 
   void CheckImplicitConversion(Expr *E, QualType T, SourceLocation CC,
                                bool *ICContext = nullptr,
                                bool IsListInit = false);
 
   bool BuiltinElementwiseTernaryMath(CallExpr *TheCall,
                                      bool CheckForFloatArgs = true);
   bool PrepareBuiltinElementwiseMathOneArgCall(CallExpr *TheCall);
 
 private:
   void CheckArrayAccess(const Expr *BaseExpr, const Expr *IndexExpr,
                         const ArraySubscriptExpr *ASE = nullptr,
                         bool AllowOnePastEnd = true, bool IndexNegated = false);
   void CheckArrayAccess(const Expr *E);
 
   bool CheckPointerCall(NamedDecl *NDecl, CallExpr *TheCall,
                         const FunctionProtoType *Proto);
 
   /// Checks function calls when a FunctionDecl or a NamedDecl is not available,
   /// such as function pointers returned from functions.
   bool CheckOtherCall(CallExpr *TheCall, const FunctionProtoType *Proto);
 
   /// CheckConstructorCall - Check a constructor call for correctness and safety
   /// properties not enforced by the C type system.
   void CheckConstructorCall(FunctionDecl *FDecl, QualType ThisType,
                             ArrayRef<const Expr *> Args,
                             const FunctionProtoType *Proto, SourceLocation Loc);
 
   /// Warn if a pointer or reference argument passed to a function points to an
   /// object that is less aligned than the parameter. This can happen when
   /// creating a typedef with a lower alignment than the original type and then
   /// calling functions defined in terms of the original type.
   void CheckArgAlignment(SourceLocation Loc, NamedDecl *FDecl,
                          StringRef ParamName, QualType ArgTy, QualType ParamTy);
 
   ExprResult CheckOSLogFormatStringArg(Expr *Arg);
 
   ExprResult CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
                                       CallExpr *TheCall);
 
   bool CheckTSBuiltinFunctionCall(const TargetInfo &TI, unsigned BuiltinID,
                                   CallExpr *TheCall);
 
   void checkFortifiedBuiltinMemoryFunction(FunctionDecl *FD, CallExpr *TheCall);
 
   /// Check the arguments to '__builtin_va_start' or '__builtin_ms_va_start'
   /// for validity.  Emit an error and return true on failure; return false
   /// on success.
   bool BuiltinVAStart(unsigned BuiltinID, CallExpr *TheCall);
   bool BuiltinVAStartARMMicrosoft(CallExpr *Call);
 
   /// BuiltinUnorderedCompare - Handle functions like __builtin_isgreater and
   /// friends.  This is declared to take (...), so we have to check everything.
   bool BuiltinUnorderedCompare(CallExpr *TheCall, unsigned BuiltinID);
 
   /// BuiltinSemaBuiltinFPClassification - Handle functions like
   /// __builtin_isnan and friends.  This is declared to take (...), so we have
   /// to check everything.
   bool BuiltinFPClassification(CallExpr *TheCall, unsigned NumArgs,
                                unsigned BuiltinID);
 
   /// Perform semantic analysis for a call to __builtin_complex.
   bool BuiltinComplex(CallExpr *TheCall);
   bool BuiltinOSLogFormat(CallExpr *TheCall);
 
   /// BuiltinPrefetch - Handle __builtin_prefetch.
   /// This is declared to take (const void*, ...) and can take two
   /// optional constant int args.
   bool BuiltinPrefetch(CallExpr *TheCall);
 
   /// Handle __builtin_alloca_with_align. This is declared
   /// as (size_t, size_t) where the second size_t must be a power of 2 greater
   /// than 8.
   bool BuiltinAllocaWithAlign(CallExpr *TheCall);
 
   /// BuiltinArithmeticFence - Handle __arithmetic_fence.
   bool BuiltinArithmeticFence(CallExpr *TheCall);
 
   /// BuiltinAssume - Handle __assume (MS Extension).
   /// __assume does not evaluate its arguments, and should warn if its argument
   /// has side effects.
   bool BuiltinAssume(CallExpr *TheCall);
 
   /// Handle __builtin_assume_aligned. This is declared
   /// as (const void*, size_t, ...) and can take one optional constant int arg.
   bool BuiltinAssumeAligned(CallExpr *TheCall);
 
   /// BuiltinLongjmp - Handle __builtin_longjmp(void *env[5], int val).
   /// This checks that the target supports __builtin_longjmp and
   /// that val is a constant 1.
   bool BuiltinLongjmp(CallExpr *TheCall);
 
   /// BuiltinSetjmp - Handle __builtin_setjmp(void *env[5]).
   /// This checks that the target supports __builtin_setjmp.
   bool BuiltinSetjmp(CallExpr *TheCall);
 
   /// We have a call to a function like __sync_fetch_and_add, which is an
   /// overloaded function based on the pointer type of its first argument.
   /// The main BuildCallExpr routines have already promoted the types of
   /// arguments because all of these calls are prototyped as void(...).
   ///
   /// This function goes through and does final semantic checking for these
   /// builtins, as well as generating any warnings.
   ExprResult BuiltinAtomicOverloaded(ExprResult TheCallResult);
 
   /// BuiltinNontemporalOverloaded - We have a call to
   /// __builtin_nontemporal_store or __builtin_nontemporal_load, which is an
   /// overloaded function based on the pointer type of its last argument.
   ///
   /// This function goes through and does final semantic checking for these
   /// builtins.
   ExprResult BuiltinNontemporalOverloaded(ExprResult TheCallResult);
   ExprResult AtomicOpsOverloaded(ExprResult TheCallResult,
                                  AtomicExpr::AtomicOp Op);
 
   /// \param FPOnly restricts the arguments to floating-point types.
   bool BuiltinElementwiseMath(CallExpr *TheCall, bool FPOnly = false);
   bool PrepareBuiltinReduceMathOneArgCall(CallExpr *TheCall);
 
   bool BuiltinNonDeterministicValue(CallExpr *TheCall);
 
   enum BuiltinCountedByRefKind {
     AssignmentKind,
     InitializerKind,
     FunctionArgKind,
     ReturnArgKind,
     ArraySubscriptKind,
     BinaryExprKind,
   };
 
   bool CheckInvalidBuiltinCountedByRef(const Expr *E,
                                        BuiltinCountedByRefKind K);
   bool BuiltinCountedByRef(CallExpr *TheCall);
 
   // Matrix builtin handling.
   ExprResult BuiltinMatrixTranspose(CallExpr *TheCall, ExprResult CallResult);
   ExprResult BuiltinMatrixColumnMajorLoad(CallExpr *TheCall,
                                           ExprResult CallResult);
   ExprResult BuiltinMatrixColumnMajorStore(CallExpr *TheCall,
                                            ExprResult CallResult);
 
   /// CheckFormatArguments - Check calls to printf and scanf (and similar
   /// functions) for correct use of format strings.
   /// Returns true if a format string has been fully checked.
   bool CheckFormatArguments(const FormatAttr *Format,
                             ArrayRef<const Expr *> Args, bool IsCXXMember,
                             VariadicCallType CallType, SourceLocation Loc,
                             SourceRange Range,
                             llvm::SmallBitVector &CheckedVarArgs);
   bool CheckFormatArguments(ArrayRef<const Expr *> Args,
                             FormatArgumentPassingKind FAPK, unsigned format_idx,
                             unsigned firstDataArg, FormatStringType Type,
                             VariadicCallType CallType, SourceLocation Loc,
                             SourceRange range,
                             llvm::SmallBitVector &CheckedVarArgs);
 
   void CheckInfNaNFunction(const CallExpr *Call, const FunctionDecl *FDecl);
 
   /// Warn when using the wrong abs() function.
   void CheckAbsoluteValueFunction(const CallExpr *Call,
                                   const FunctionDecl *FDecl);
 
   void CheckMaxUnsignedZero(const CallExpr *Call, const FunctionDecl *FDecl);
 
   /// Check for dangerous or invalid arguments to memset().
   ///
   /// This issues warnings on known problematic, dangerous or unspecified
   /// arguments to the standard 'memset', 'memcpy', 'memmove', and 'memcmp'
   /// function calls.
   ///
   /// \param Call The call expression to diagnose.
   void CheckMemaccessArguments(const CallExpr *Call, unsigned BId,
                                IdentifierInfo *FnName);
 
   // Warn if the user has made the 'size' argument to strlcpy or strlcat
   // be the size of the source, instead of the destination.
   void CheckStrlcpycatArguments(const CallExpr *Call, IdentifierInfo *FnName);
 
   // Warn on anti-patterns as the 'size' argument to strncat.
   // The correct size argument should look like following:
   //   strncat(dst, src, sizeof(dst) - strlen(dest) - 1);
   void CheckStrncatArguments(const CallExpr *Call, IdentifierInfo *FnName);
 
   /// Alerts the user that they are attempting to free a non-malloc'd object.
   void CheckFreeArguments(const CallExpr *E);
 
   void CheckReturnValExpr(Expr *RetValExp, QualType lhsType,
                           SourceLocation ReturnLoc, bool isObjCMethod = false,
                           const AttrVec *Attrs = nullptr,
                           const FunctionDecl *FD = nullptr);
 
   /// Diagnoses "dangerous" implicit conversions within the given
   /// expression (which is a full expression).  Implements -Wconversion
   /// and -Wsign-compare.
   ///
   /// \param CC the "context" location of the implicit conversion, i.e.
   ///   the most location of the syntactic entity requiring the implicit
   ///   conversion
   void CheckImplicitConversions(Expr *E, SourceLocation CC = SourceLocation());
 
   /// CheckBoolLikeConversion - Check conversion of given expression to boolean.
   /// Input argument E is a logical expression.
   void CheckBoolLikeConversion(Expr *E, SourceLocation CC);
 
   /// Diagnose when expression is an integer constant expression and its
   /// evaluation results in integer overflow
   void CheckForIntOverflow(const Expr *E);
   void CheckUnsequencedOperations(const Expr *E);
 
   /// Perform semantic checks on a completed expression. This will either
   /// be a full-expression or a default argument expression.
   void CheckCompletedExpr(Expr *E, SourceLocation CheckLoc = SourceLocation(),
                           bool IsConstexpr = false);
 
   void CheckBitFieldInitialization(SourceLocation InitLoc, FieldDecl *Field,
                                    Expr *Init);
 
   /// A map from magic value to type information.
   std::unique_ptr<llvm::DenseMap<TypeTagMagicValue, TypeTagData>>
       TypeTagForDatatypeMagicValues;
 
   /// Peform checks on a call of a function with argument_with_type_tag
   /// or pointer_with_type_tag attributes.
   void CheckArgumentWithTypeTag(const ArgumentWithTypeTagAttr *Attr,
                                 const ArrayRef<const Expr *> ExprArgs,
                                 SourceLocation CallSiteLoc);
 
   /// Check if we are taking the address of a packed field
   /// as this may be a problem if the pointer value is dereferenced.
   void CheckAddressOfPackedMember(Expr *rhs);
 
   /// Helper class that collects misaligned member designations and
   /// their location info for delayed diagnostics.
   struct MisalignedMember {
     Expr *E;
     RecordDecl *RD;
     ValueDecl *MD;
     CharUnits Alignment;
 
     MisalignedMember() : E(), RD(), MD() {}
     MisalignedMember(Expr *E, RecordDecl *RD, ValueDecl *MD,
                      CharUnits Alignment)
         : E(E), RD(RD), MD(MD), Alignment(Alignment) {}
     explicit MisalignedMember(Expr *E)
         : MisalignedMember(E, nullptr, nullptr, CharUnits()) {}
 
     bool operator==(const MisalignedMember &m) { return this->E == m.E; }
   };
   /// Small set of gathered accesses to potentially misaligned members
   /// due to the packed attribute.
   SmallVector<MisalignedMember, 4> MisalignedMembers;
 
   /// Adds an expression to the set of gathered misaligned members.
   void AddPotentialMisalignedMembers(Expr *E, RecordDecl *RD, ValueDecl *MD,
                                      CharUnits Alignment);
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Coroutines
   /// Implementations are in SemaCoroutine.cpp
   ///@{
 
 public:
   /// The C++ "std::coroutine_traits" template, which is defined in
   /// \<coroutine_traits>
   ClassTemplateDecl *StdCoroutineTraitsCache;
 
   bool ActOnCoroutineBodyStart(Scope *S, SourceLocation KwLoc,
                                StringRef Keyword);
   ExprResult ActOnCoawaitExpr(Scope *S, SourceLocation KwLoc, Expr *E);
   ExprResult ActOnCoyieldExpr(Scope *S, SourceLocation KwLoc, Expr *E);
   StmtResult ActOnCoreturnStmt(Scope *S, SourceLocation KwLoc, Expr *E);
 
   ExprResult BuildOperatorCoawaitLookupExpr(Scope *S, SourceLocation Loc);
   ExprResult BuildOperatorCoawaitCall(SourceLocation Loc, Expr *E,
                                       UnresolvedLookupExpr *Lookup);
   ExprResult BuildResolvedCoawaitExpr(SourceLocation KwLoc, Expr *Operand,
                                       Expr *Awaiter, bool IsImplicit = false);
   ExprResult BuildUnresolvedCoawaitExpr(SourceLocation KwLoc, Expr *Operand,
                                         UnresolvedLookupExpr *Lookup);
   ExprResult BuildCoyieldExpr(SourceLocation KwLoc, Expr *E);
   StmtResult BuildCoreturnStmt(SourceLocation KwLoc, Expr *E,
                                bool IsImplicit = false);
   StmtResult BuildCoroutineBodyStmt(CoroutineBodyStmt::CtorArgs);
   bool buildCoroutineParameterMoves(SourceLocation Loc);
   VarDecl *buildCoroutinePromise(SourceLocation Loc);
   void CheckCompletedCoroutineBody(FunctionDecl *FD, Stmt *&Body);
 
   // As a clang extension, enforces that a non-coroutine function must be marked
   // with [[clang::coro_wrapper]] if it returns a type marked with
   // [[clang::coro_return_type]].
   // Expects that FD is not a coroutine.
   void CheckCoroutineWrapper(FunctionDecl *FD);
   /// Lookup 'coroutine_traits' in std namespace and std::experimental
   /// namespace. The namespace found is recorded in Namespace.
   ClassTemplateDecl *lookupCoroutineTraits(SourceLocation KwLoc,
                                            SourceLocation FuncLoc);
   /// Check that the expression co_await promise.final_suspend() shall not be
   /// potentially-throwing.
   bool checkFinalSuspendNoThrow(const Stmt *FinalSuspend);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Scope Specifiers
   /// Implementations are in SemaCXXScopeSpec.cpp
   ///@{
 
 public:
   // Marks SS invalid if it represents an incomplete type.
   bool RequireCompleteDeclContext(CXXScopeSpec &SS, DeclContext *DC);
   // Complete an enum decl, maybe without a scope spec.
   bool RequireCompleteEnumDecl(EnumDecl *D, SourceLocation L,
                                CXXScopeSpec *SS = nullptr);
 
   /// Compute the DeclContext that is associated with the given type.
   ///
   /// \param T the type for which we are attempting to find a DeclContext.
   ///
   /// \returns the declaration context represented by the type T,
   /// or NULL if the declaration context cannot be computed (e.g., because it is
   /// dependent and not the current instantiation).
   DeclContext *computeDeclContext(QualType T);
 
   /// Compute the DeclContext that is associated with the given
   /// scope specifier.
   ///
   /// \param SS the C++ scope specifier as it appears in the source
   ///
   /// \param EnteringContext when true, we will be entering the context of
   /// this scope specifier, so we can retrieve the declaration context of a
   /// class template or class template partial specialization even if it is
   /// not the current instantiation.
   ///
   /// \returns the declaration context represented by the scope specifier @p SS,
   /// or NULL if the declaration context cannot be computed (e.g., because it is
   /// dependent and not the current instantiation).
   DeclContext *computeDeclContext(const CXXScopeSpec &SS,
                                   bool EnteringContext = false);
   bool isDependentScopeSpecifier(const CXXScopeSpec &SS);
 
   /// If the given nested name specifier refers to the current
   /// instantiation, return the declaration that corresponds to that
   /// current instantiation (C++0x [temp.dep.type]p1).
   ///
   /// \param NNS a dependent nested name specifier.
   CXXRecordDecl *getCurrentInstantiationOf(NestedNameSpecifier *NNS);
 
   /// The parser has parsed a global nested-name-specifier '::'.
   ///
   /// \param CCLoc The location of the '::'.
   ///
   /// \param SS The nested-name-specifier, which will be updated in-place
   /// to reflect the parsed nested-name-specifier.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool ActOnCXXGlobalScopeSpecifier(SourceLocation CCLoc, CXXScopeSpec &SS);
 
   /// The parser has parsed a '__super' nested-name-specifier.
   ///
   /// \param SuperLoc The location of the '__super' keyword.
   ///
   /// \param ColonColonLoc The location of the '::'.
   ///
   /// \param SS The nested-name-specifier, which will be updated in-place
   /// to reflect the parsed nested-name-specifier.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool ActOnSuperScopeSpecifier(SourceLocation SuperLoc,
                                 SourceLocation ColonColonLoc, CXXScopeSpec &SS);
 
   /// Determines whether the given declaration is an valid acceptable
   /// result for name lookup of a nested-name-specifier.
   /// \param SD Declaration checked for nested-name-specifier.
   /// \param IsExtension If not null and the declaration is accepted as an
   /// extension, the pointed variable is assigned true.
   bool isAcceptableNestedNameSpecifier(const NamedDecl *SD,
                                        bool *CanCorrect = nullptr);
 
   /// If the given nested-name-specifier begins with a bare identifier
   /// (e.g., Base::), perform name lookup for that identifier as a
   /// nested-name-specifier within the given scope, and return the result of
   /// that name lookup.
   NamedDecl *FindFirstQualifierInScope(Scope *S, NestedNameSpecifier *NNS);
 
   /// Keeps information about an identifier in a nested-name-spec.
   ///
   struct NestedNameSpecInfo {
     /// The type of the object, if we're parsing nested-name-specifier in
     /// a member access expression.
     ParsedType ObjectType;
 
     /// The identifier preceding the '::'.
     IdentifierInfo *Identifier;
 
     /// The location of the identifier.
     SourceLocation IdentifierLoc;
 
     /// The location of the '::'.
     SourceLocation CCLoc;
 
     /// Creates info object for the most typical case.
     NestedNameSpecInfo(IdentifierInfo *II, SourceLocation IdLoc,
                        SourceLocation ColonColonLoc,
                        ParsedType ObjectType = ParsedType())
         : ObjectType(ObjectType), Identifier(II), IdentifierLoc(IdLoc),
           CCLoc(ColonColonLoc) {}
 
     NestedNameSpecInfo(IdentifierInfo *II, SourceLocation IdLoc,
                        SourceLocation ColonColonLoc, QualType ObjectType)
         : ObjectType(ParsedType::make(ObjectType)), Identifier(II),
           IdentifierLoc(IdLoc), CCLoc(ColonColonLoc) {}
   };
 
   /// Build a new nested-name-specifier for "identifier::", as described
   /// by ActOnCXXNestedNameSpecifier.
   ///
   /// \param S Scope in which the nested-name-specifier occurs.
   /// \param IdInfo Parser information about an identifier in the
   ///        nested-name-spec.
   /// \param EnteringContext If true, enter the context specified by the
   ///        nested-name-specifier.
   /// \param SS Optional nested name specifier preceding the identifier.
   /// \param ScopeLookupResult Provides the result of name lookup within the
   ///        scope of the nested-name-specifier that was computed at template
   ///        definition time.
   /// \param ErrorRecoveryLookup Specifies if the method is called to improve
   ///        error recovery and what kind of recovery is performed.
   /// \param IsCorrectedToColon If not null, suggestion of replace '::' -> ':'
   ///        are allowed.  The bool value pointed by this parameter is set to
   ///       'true' if the identifier is treated as if it was followed by ':',
   ///        not '::'.
   /// \param OnlyNamespace If true, only considers namespaces in lookup.
   ///
   /// This routine differs only slightly from ActOnCXXNestedNameSpecifier, in
   /// that it contains an extra parameter \p ScopeLookupResult, which provides
   /// the result of name lookup within the scope of the nested-name-specifier
   /// that was computed at template definition time.
   ///
   /// If ErrorRecoveryLookup is true, then this call is used to improve error
   /// recovery.  This means that it should not emit diagnostics, it should
   /// just return true on failure.  It also means it should only return a valid
   /// scope if it *knows* that the result is correct.  It should not return in a
   /// dependent context, for example. Nor will it extend \p SS with the scope
   /// specifier.
   bool BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
                                    bool EnteringContext, CXXScopeSpec &SS,
                                    NamedDecl *ScopeLookupResult,
                                    bool ErrorRecoveryLookup,
                                    bool *IsCorrectedToColon = nullptr,
                                    bool OnlyNamespace = false);
 
   /// The parser has parsed a nested-name-specifier 'identifier::'.
   ///
   /// \param S The scope in which this nested-name-specifier occurs.
   ///
   /// \param IdInfo Parser information about an identifier in the
   /// nested-name-spec.
   ///
   /// \param EnteringContext Whether we're entering the context nominated by
   /// this nested-name-specifier.
   ///
   /// \param SS The nested-name-specifier, which is both an input
   /// parameter (the nested-name-specifier before this type) and an
   /// output parameter (containing the full nested-name-specifier,
   /// including this new type).
   ///
   /// \param IsCorrectedToColon If not null, suggestions to replace '::' -> ':'
   /// are allowed.  The bool value pointed by this parameter is set to 'true'
   /// if the identifier is treated as if it was followed by ':', not '::'.
   ///
   /// \param OnlyNamespace If true, only considers namespaces in lookup.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool ActOnCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
                                    bool EnteringContext, CXXScopeSpec &SS,
                                    bool *IsCorrectedToColon = nullptr,
                                    bool OnlyNamespace = false);
 
   /// The parser has parsed a nested-name-specifier
   /// 'template[opt] template-name < template-args >::'.
   ///
   /// \param S The scope in which this nested-name-specifier occurs.
   ///
   /// \param SS The nested-name-specifier, which is both an input
   /// parameter (the nested-name-specifier before this type) and an
   /// output parameter (containing the full nested-name-specifier,
   /// including this new type).
   ///
   /// \param TemplateKWLoc the location of the 'template' keyword, if any.
   /// \param TemplateName the template name.
   /// \param TemplateNameLoc The location of the template name.
   /// \param LAngleLoc The location of the opening angle bracket  ('<').
   /// \param TemplateArgs The template arguments.
   /// \param RAngleLoc The location of the closing angle bracket  ('>').
   /// \param CCLoc The location of the '::'.
   ///
   /// \param EnteringContext Whether we're entering the context of the
   /// nested-name-specifier.
   ///
   ///
   /// \returns true if an error occurred, false otherwise.
   bool ActOnCXXNestedNameSpecifier(
       Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
       TemplateTy TemplateName, SourceLocation TemplateNameLoc,
       SourceLocation LAngleLoc, ASTTemplateArgsPtr TemplateArgs,
       SourceLocation RAngleLoc, SourceLocation CCLoc, bool EnteringContext);
 
   bool ActOnCXXNestedNameSpecifierDecltype(CXXScopeSpec &SS, const DeclSpec &DS,
                                            SourceLocation ColonColonLoc);
 
   bool ActOnCXXNestedNameSpecifierIndexedPack(CXXScopeSpec &SS,
                                               const DeclSpec &DS,
                                               SourceLocation ColonColonLoc,
                                               QualType Type);
 
   /// IsInvalidUnlessNestedName - This method is used for error recovery
   /// purposes to determine whether the specified identifier is only valid as
   /// a nested name specifier, for example a namespace name.  It is
   /// conservatively correct to always return false from this method.
   ///
   /// The arguments are the same as those passed to ActOnCXXNestedNameSpecifier.
   bool IsInvalidUnlessNestedName(Scope *S, CXXScopeSpec &SS,
                                  NestedNameSpecInfo &IdInfo,
                                  bool EnteringContext);
 
   /// Given a C++ nested-name-specifier, produce an annotation value
   /// that the parser can use later to reconstruct the given
   /// nested-name-specifier.
   ///
   /// \param SS A nested-name-specifier.
   ///
   /// \returns A pointer containing all of the information in the
   /// nested-name-specifier \p SS.
   void *SaveNestedNameSpecifierAnnotation(CXXScopeSpec &SS);
 
   /// Given an annotation pointer for a nested-name-specifier, restore
   /// the nested-name-specifier structure.
   ///
   /// \param Annotation The annotation pointer, produced by
   /// \c SaveNestedNameSpecifierAnnotation().
   ///
   /// \param AnnotationRange The source range corresponding to the annotation.
   ///
   /// \param SS The nested-name-specifier that will be updated with the contents
   /// of the annotation pointer.
   void RestoreNestedNameSpecifierAnnotation(void *Annotation,
                                             SourceRange AnnotationRange,
                                             CXXScopeSpec &SS);
 
   bool ShouldEnterDeclaratorScope(Scope *S, const CXXScopeSpec &SS);
 
   /// ActOnCXXEnterDeclaratorScope - Called when a C++ scope specifier (global
   /// scope or nested-name-specifier) is parsed, part of a declarator-id.
   /// After this method is called, according to [C++ 3.4.3p3], names should be
   /// looked up in the declarator-id's scope, until the declarator is parsed and
   /// ActOnCXXExitDeclaratorScope is called.
   /// The 'SS' should be a non-empty valid CXXScopeSpec.
   bool ActOnCXXEnterDeclaratorScope(Scope *S, CXXScopeSpec &SS);
 
   /// ActOnCXXExitDeclaratorScope - Called when a declarator that previously
   /// invoked ActOnCXXEnterDeclaratorScope(), is finished. 'SS' is the same
   /// CXXScopeSpec that was passed to ActOnCXXEnterDeclaratorScope as well.
   /// Used to indicate that names should revert to being looked up in the
   /// defining scope.
   void ActOnCXXExitDeclaratorScope(Scope *S, const CXXScopeSpec &SS);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Declarations
   /// Implementations are in SemaDecl.cpp
   ///@{
 
 public:
   IdentifierResolver IdResolver;
 
   /// The index of the first InventedParameterInfo that refers to the current
   /// context.
   unsigned InventedParameterInfosStart = 0;
 
   /// A RAII object to temporarily push a declaration context.
   class ContextRAII {
   private:
     Sema &S;
     DeclContext *SavedContext;
     ProcessingContextState SavedContextState;
     QualType SavedCXXThisTypeOverride;
     unsigned SavedFunctionScopesStart;
     unsigned SavedInventedParameterInfosStart;
 
   public:
     ContextRAII(Sema &S, DeclContext *ContextToPush, bool NewThisContext = true)
         : S(S), SavedContext(S.CurContext),
           SavedContextState(S.DelayedDiagnostics.pushUndelayed()),
           SavedCXXThisTypeOverride(S.CXXThisTypeOverride),
           SavedFunctionScopesStart(S.FunctionScopesStart),
           SavedInventedParameterInfosStart(S.InventedParameterInfosStart) {
       assert(ContextToPush && "pushing null context");
       S.CurContext = ContextToPush;
       if (NewThisContext)
         S.CXXThisTypeOverride = QualType();
       // Any saved FunctionScopes do not refer to this context.
       S.FunctionScopesStart = S.FunctionScopes.size();
       S.InventedParameterInfosStart = S.InventedParameterInfos.size();
     }
 
     void pop() {
       if (!SavedContext)
         return;
       S.CurContext = SavedContext;
       S.DelayedDiagnostics.popUndelayed(SavedContextState);
       S.CXXThisTypeOverride = SavedCXXThisTypeOverride;
       S.FunctionScopesStart = SavedFunctionScopesStart;
       S.InventedParameterInfosStart = SavedInventedParameterInfosStart;
       SavedContext = nullptr;
     }
 
     ~ContextRAII() { pop(); }
   };
 
   void DiagnoseInvalidJumps(Stmt *Body);
 
   /// The function definitions which were renamed as part of typo-correction
   /// to match their respective declarations. We want to keep track of them
   /// to ensure that we don't emit a "redefinition" error if we encounter a
   /// correctly named definition after the renamed definition.
   llvm::SmallPtrSet<const NamedDecl *, 4> TypoCorrectedFunctionDefinitions;
 
   /// A cache of the flags available in enumerations with the flag_bits
   /// attribute.
   mutable llvm::DenseMap<const EnumDecl *, llvm::APInt> FlagBitsCache;
 
   /// WeakUndeclaredIdentifiers - Identifiers contained in \#pragma weak before
   /// declared. Rare. May alias another identifier, declared or undeclared.
   ///
   /// For aliases, the target identifier is used as a key for eventual
   /// processing when the target is declared. For the single-identifier form,
   /// the sole identifier is used as the key. Each entry is a `SetVector`
   /// (ordered by parse order) of aliases (identified by the alias name) in case
   /// of multiple aliases to the same undeclared identifier.
   llvm::MapVector<
       IdentifierInfo *,
       llvm::SetVector<
           WeakInfo, llvm::SmallVector<WeakInfo, 1u>,
           llvm::SmallDenseSet<WeakInfo, 2u, WeakInfo::DenseMapInfoByAliasOnly>>>
       WeakUndeclaredIdentifiers;
 
   /// ExtnameUndeclaredIdentifiers - Identifiers contained in
   /// \#pragma redefine_extname before declared.  Used in Solaris system headers
   /// to define functions that occur in multiple standards to call the version
   /// in the currently selected standard.
   llvm::DenseMap<IdentifierInfo *, AsmLabelAttr *> ExtnameUndeclaredIdentifiers;
 
   /// Set containing all typedefs that are likely unused.
   llvm::SmallSetVector<const TypedefNameDecl *, 4>
       UnusedLocalTypedefNameCandidates;
 
   typedef LazyVector<const DeclaratorDecl *, ExternalSemaSource,
                      &ExternalSemaSource::ReadUnusedFileScopedDecls, 2, 2>
       UnusedFileScopedDeclsType;
 
   /// The set of file scoped decls seen so far that have not been used
   /// and must warn if not used. Only contains the first declaration.
   UnusedFileScopedDeclsType UnusedFileScopedDecls;
 
   typedef LazyVector<VarDecl *, ExternalSemaSource,
                      &ExternalSemaSource::ReadTentativeDefinitions, 2, 2>
       TentativeDefinitionsType;
 
   /// All the tentative definitions encountered in the TU.
   TentativeDefinitionsType TentativeDefinitions;
 
   /// All the external declarations encoutered and used in the TU.
   SmallVector<DeclaratorDecl *, 4> ExternalDeclarations;
 
   /// Generally null except when we temporarily switch decl contexts,
   /// like in \see SemaObjC::ActOnObjCTemporaryExitContainerContext.
   DeclContext *OriginalLexicalContext;
 
   /// Is the module scope we are in a C++ Header Unit?
   bool currentModuleIsHeaderUnit() const {
     return ModuleScopes.empty() ? false
                                 : ModuleScopes.back().Module->isHeaderUnit();
   }
 
   /// Get the module owning an entity.
   Module *getOwningModule(const Decl *Entity) {
     return Entity->getOwningModule();
   }
 
   DeclGroupPtrTy ConvertDeclToDeclGroup(Decl *Ptr, Decl *OwnedType = nullptr);
 
   /// If the identifier refers to a type name within this scope,
   /// return the declaration of that type.
   ///
   /// This routine performs ordinary name lookup of the identifier II
   /// within the given scope, with optional C++ scope specifier SS, to
   /// determine whether the name refers to a type. If so, returns an
   /// opaque pointer (actually a QualType) corresponding to that
   /// type. Otherwise, returns NULL.
   ParsedType getTypeName(const IdentifierInfo &II, SourceLocation NameLoc,
                          Scope *S, CXXScopeSpec *SS = nullptr,
                          bool isClassName = false, bool HasTrailingDot = false,
                          ParsedType ObjectType = nullptr,
                          bool IsCtorOrDtorName = false,
                          bool WantNontrivialTypeSourceInfo = false,
                          bool IsClassTemplateDeductionContext = true,
                          ImplicitTypenameContext AllowImplicitTypename =
                              ImplicitTypenameContext::No,
                          IdentifierInfo **CorrectedII = nullptr);
 
   /// isTagName() - This method is called *for error recovery purposes only*
   /// to determine if the specified name is a valid tag name ("struct foo").  If
   /// so, this returns the TST for the tag corresponding to it (TST_enum,
   /// TST_union, TST_struct, TST_interface, TST_class).  This is used to
   /// diagnose cases in C where the user forgot to specify the tag.
   TypeSpecifierType isTagName(IdentifierInfo &II, Scope *S);
 
   /// isMicrosoftMissingTypename - In Microsoft mode, within class scope,
   /// if a CXXScopeSpec's type is equal to the type of one of the base classes
   /// then downgrade the missing typename error to a warning.
   /// This is needed for MSVC compatibility; Example:
   /// @code
   /// template<class T> class A {
   /// public:
   ///   typedef int TYPE;
   /// };
   /// template<class T> class B : public A<T> {
   /// public:
   ///   A<T>::TYPE a; // no typename required because A<T> is a base class.
   /// };
   /// @endcode
   bool isMicrosoftMissingTypename(const CXXScopeSpec *SS, Scope *S);
   void DiagnoseUnknownTypeName(IdentifierInfo *&II, SourceLocation IILoc,
                                Scope *S, CXXScopeSpec *SS,
                                ParsedType &SuggestedType,
                                bool IsTemplateName = false);
 
   /// Attempt to behave like MSVC in situations where lookup of an unqualified
   /// type name has failed in a dependent context. In these situations, we
   /// automatically form a DependentTypeName that will retry lookup in a related
   /// scope during instantiation.
   ParsedType ActOnMSVCUnknownTypeName(const IdentifierInfo &II,
                                       SourceLocation NameLoc,
                                       bool IsTemplateTypeArg);
 
   /// Describes the result of the name lookup and resolution performed
   /// by \c ClassifyName().
   enum NameClassificationKind {
     /// This name is not a type or template in this context, but might be
     /// something else.
     NC_Unknown,
     /// Classification failed; an error has been produced.
     NC_Error,
     /// The name has been typo-corrected to a keyword.
     NC_Keyword,
     /// The name was classified as a type.
     NC_Type,
     /// The name was classified as a specific non-type, non-template
     /// declaration. ActOnNameClassifiedAsNonType should be called to
     /// convert the declaration to an expression.
     NC_NonType,
     /// The name was classified as an ADL-only function name.
     /// ActOnNameClassifiedAsUndeclaredNonType should be called to convert the
     /// result to an expression.
     NC_UndeclaredNonType,
     /// The name denotes a member of a dependent type that could not be
     /// resolved. ActOnNameClassifiedAsDependentNonType should be called to
     /// convert the result to an expression.
     NC_DependentNonType,
     /// The name was classified as an overload set, and an expression
     /// representing that overload set has been formed.
     /// ActOnNameClassifiedAsOverloadSet should be called to form a suitable
     /// expression referencing the overload set.
     NC_OverloadSet,
     /// The name was classified as a template whose specializations are types.
     NC_TypeTemplate,
     /// The name was classified as a variable template name.
     NC_VarTemplate,
     /// The name was classified as a function template name.
     NC_FunctionTemplate,
     /// The name was classified as an ADL-only function template name.
     NC_UndeclaredTemplate,
     /// The name was classified as a concept name.
     NC_Concept,
   };
 
   class NameClassification {
     NameClassificationKind Kind;
     union {
       ExprResult Expr;
       NamedDecl *NonTypeDecl;
       TemplateName Template;
       ParsedType Type;
     };
 
     explicit NameClassification(NameClassificationKind Kind) : Kind(Kind) {}
 
   public:
     NameClassification(ParsedType Type) : Kind(NC_Type), Type(Type) {}
 
     NameClassification(const IdentifierInfo *Keyword) : Kind(NC_Keyword) {}
 
     static NameClassification Error() { return NameClassification(NC_Error); }
 
     static NameClassification Unknown() {
       return NameClassification(NC_Unknown);
     }
 
     static NameClassification OverloadSet(ExprResult E) {
       NameClassification Result(NC_OverloadSet);
       Result.Expr = E;
       return Result;
     }
 
     static NameClassification NonType(NamedDecl *D) {
       NameClassification Result(NC_NonType);
       Result.NonTypeDecl = D;
       return Result;
     }
 
     static NameClassification UndeclaredNonType() {
       return NameClassification(NC_UndeclaredNonType);
     }
 
     static NameClassification DependentNonType() {
       return NameClassification(NC_DependentNonType);
     }
 
     static NameClassification TypeTemplate(TemplateName Name) {
       NameClassification Result(NC_TypeTemplate);
       Result.Template = Name;
       return Result;
     }
 
     static NameClassification VarTemplate(TemplateName Name) {
       NameClassification Result(NC_VarTemplate);
       Result.Template = Name;
       return Result;
     }
 
     static NameClassification FunctionTemplate(TemplateName Name) {
       NameClassification Result(NC_FunctionTemplate);
       Result.Template = Name;
       return Result;
     }
 
     static NameClassification Concept(TemplateName Name) {
       NameClassification Result(NC_Concept);
       Result.Template = Name;
       return Result;
     }
 
     static NameClassification UndeclaredTemplate(TemplateName Name) {
       NameClassification Result(NC_UndeclaredTemplate);
       Result.Template = Name;
       return Result;
     }
 
     NameClassificationKind getKind() const { return Kind; }
 
     ExprResult getExpression() const {
       assert(Kind == NC_OverloadSet);
       return Expr;
     }
 
     ParsedType getType() const {
       assert(Kind == NC_Type);
       return Type;
     }
 
     NamedDecl *getNonTypeDecl() const {
       assert(Kind == NC_NonType);
       return NonTypeDecl;
     }
 
     TemplateName getTemplateName() const {
       assert(Kind == NC_TypeTemplate || Kind == NC_FunctionTemplate ||
              Kind == NC_VarTemplate || Kind == NC_Concept ||
              Kind == NC_UndeclaredTemplate);
       return Template;
     }
 
     TemplateNameKind getTemplateNameKind() const {
       switch (Kind) {
       case NC_TypeTemplate:
         return TNK_Type_template;
       case NC_FunctionTemplate:
         return TNK_Function_template;
       case NC_VarTemplate:
         return TNK_Var_template;
       case NC_Concept:
         return TNK_Concept_template;
       case NC_UndeclaredTemplate:
         return TNK_Undeclared_template;
       default:
         llvm_unreachable("unsupported name classification.");
       }
     }
   };
 
   /// Perform name lookup on the given name, classifying it based on
   /// the results of name lookup and the following token.
   ///
   /// This routine is used by the parser to resolve identifiers and help direct
   /// parsing. When the identifier cannot be found, this routine will attempt
   /// to correct the typo and classify based on the resulting name.
   ///
   /// \param S The scope in which we're performing name lookup.
   ///
   /// \param SS The nested-name-specifier that precedes the name.
   ///
   /// \param Name The identifier. If typo correction finds an alternative name,
   /// this pointer parameter will be updated accordingly.
   ///
   /// \param NameLoc The location of the identifier.
   ///
   /// \param NextToken The token following the identifier. Used to help
   /// disambiguate the name.
   ///
   /// \param CCC The correction callback, if typo correction is desired.
   NameClassification ClassifyName(Scope *S, CXXScopeSpec &SS,
                                   IdentifierInfo *&Name, SourceLocation NameLoc,
                                   const Token &NextToken,
                                   CorrectionCandidateCallback *CCC = nullptr);
 
   /// Act on the result of classifying a name as an undeclared (ADL-only)
   /// non-type declaration.
   ExprResult ActOnNameClassifiedAsUndeclaredNonType(IdentifierInfo *Name,
                                                     SourceLocation NameLoc);
   /// Act on the result of classifying a name as an undeclared member of a
   /// dependent base class.
   ExprResult ActOnNameClassifiedAsDependentNonType(const CXXScopeSpec &SS,
                                                    IdentifierInfo *Name,
                                                    SourceLocation NameLoc,
                                                    bool IsAddressOfOperand);
   /// Act on the result of classifying a name as a specific non-type
   /// declaration.
   ExprResult ActOnNameClassifiedAsNonType(Scope *S, const CXXScopeSpec &SS,
                                           NamedDecl *Found,
                                           SourceLocation NameLoc,
                                           const Token &NextToken);
   /// Act on the result of classifying a name as an overload set.
   ExprResult ActOnNameClassifiedAsOverloadSet(Scope *S, Expr *OverloadSet);
 
   /// Describes the detailed kind of a template name. Used in diagnostics.
   enum class TemplateNameKindForDiagnostics {
     ClassTemplate,
     FunctionTemplate,
     VarTemplate,
     AliasTemplate,
     TemplateTemplateParam,
     Concept,
     DependentTemplate
   };
   TemplateNameKindForDiagnostics
   getTemplateNameKindForDiagnostics(TemplateName Name);
 
   /// Determine whether it's plausible that E was intended to be a
   /// template-name.
   bool mightBeIntendedToBeTemplateName(ExprResult E, bool &Dependent) {
     if (!getLangOpts().CPlusPlus || E.isInvalid())
       return false;
     Dependent = false;
     if (auto *DRE = dyn_cast<DeclRefExpr>(E.get()))
       return !DRE->hasExplicitTemplateArgs();
     if (auto *ME = dyn_cast<MemberExpr>(E.get()))
       return !ME->hasExplicitTemplateArgs();
     Dependent = true;
     if (auto *DSDRE = dyn_cast<DependentScopeDeclRefExpr>(E.get()))
       return !DSDRE->hasExplicitTemplateArgs();
     if (auto *DSME = dyn_cast<CXXDependentScopeMemberExpr>(E.get()))
       return !DSME->hasExplicitTemplateArgs();
     // Any additional cases recognized here should also be handled by
     // diagnoseExprIntendedAsTemplateName.
     return false;
   }
 
   void warnOnReservedIdentifier(const NamedDecl *D);
 
   Decl *ActOnDeclarator(Scope *S, Declarator &D);
 
   NamedDecl *HandleDeclarator(Scope *S, Declarator &D,
                               MultiTemplateParamsArg TemplateParameterLists);
 
   /// Attempt to fold a variable-sized type to a constant-sized type, returning
   /// true if we were successful.
   bool tryToFixVariablyModifiedVarType(TypeSourceInfo *&TInfo, QualType &T,
                                        SourceLocation Loc,
                                        unsigned FailedFoldDiagID);
 
   /// Register the given locally-scoped extern "C" declaration so
   /// that it can be found later for redeclarations. We include any extern "C"
   /// declaration that is not visible in the translation unit here, not just
   /// function-scope declarations.
   void RegisterLocallyScopedExternCDecl(NamedDecl *ND, Scope *S);
 
   /// DiagnoseClassNameShadow - Implement C++ [class.mem]p13:
   ///   If T is the name of a class, then each of the following shall have a
   ///   name different from T:
   ///     - every static data member of class T;
   ///     - every member function of class T
   ///     - every member of class T that is itself a type;
   /// \returns true if the declaration name violates these rules.
   bool DiagnoseClassNameShadow(DeclContext *DC, DeclarationNameInfo Info);
 
   /// Diagnose a declaration whose declarator-id has the given
   /// nested-name-specifier.
   ///
   /// \param SS The nested-name-specifier of the declarator-id.
   ///
   /// \param DC The declaration context to which the nested-name-specifier
   /// resolves.
   ///
   /// \param Name The name of the entity being declared.
   ///
   /// \param Loc The location of the name of the entity being declared.
   ///
   /// \param IsMemberSpecialization Whether we are declaring a member
   /// specialization.
   ///
   /// \param TemplateId The template-id, if any.
   ///
   /// \returns true if we cannot safely recover from this error, false
   /// otherwise.
   bool diagnoseQualifiedDeclaration(CXXScopeSpec &SS, DeclContext *DC,
                                     DeclarationName Name, SourceLocation Loc,
                                     TemplateIdAnnotation *TemplateId,
                                     bool IsMemberSpecialization);
 
   bool checkPointerAuthEnabled(SourceLocation Loc, SourceRange Range);
 
   bool checkConstantPointerAuthKey(Expr *keyExpr, unsigned &key);
 
   /// Diagnose function specifiers on a declaration of an identifier that
   /// does not identify a function.
   void DiagnoseFunctionSpecifiers(const DeclSpec &DS);
 
   /// Return the declaration shadowed by the given typedef \p D, or null
   /// if it doesn't shadow any declaration or shadowing warnings are disabled.
   NamedDecl *getShadowedDeclaration(const TypedefNameDecl *D,
                                     const LookupResult &R);
 
   /// Return the declaration shadowed by the given variable \p D, or null
   /// if it doesn't shadow any declaration or shadowing warnings are disabled.
   NamedDecl *getShadowedDeclaration(const VarDecl *D, const LookupResult &R);
 
   /// Return the declaration shadowed by the given variable \p D, or null
   /// if it doesn't shadow any declaration or shadowing warnings are disabled.
   NamedDecl *getShadowedDeclaration(const BindingDecl *D,
                                     const LookupResult &R);
   /// Diagnose variable or built-in function shadowing.  Implements
   /// -Wshadow.
   ///
   /// This method is called whenever a VarDecl is added to a "useful"
   /// scope.
   ///
   /// \param ShadowedDecl the declaration that is shadowed by the given variable
   /// \param R the lookup of the name
   void CheckShadow(NamedDecl *D, NamedDecl *ShadowedDecl,
                    const LookupResult &R);
 
   /// Check -Wshadow without the advantage of a previous lookup.
   void CheckShadow(Scope *S, VarDecl *D);
 
   /// Warn if 'E', which is an expression that is about to be modified, refers
   /// to a shadowing declaration.
   void CheckShadowingDeclModification(Expr *E, SourceLocation Loc);
 
   /// Diagnose shadowing for variables shadowed in the lambda record \p LambdaRD
   /// when these variables are captured by the lambda.
   void DiagnoseShadowingLambdaDecls(const sema::LambdaScopeInfo *LSI);
 
   void handleTagNumbering(const TagDecl *Tag, Scope *TagScope);
   void setTagNameForLinkagePurposes(TagDecl *TagFromDeclSpec,
                                     TypedefNameDecl *NewTD);
   void CheckTypedefForVariablyModifiedType(Scope *S, TypedefNameDecl *D);
   NamedDecl *ActOnTypedefDeclarator(Scope *S, Declarator &D, DeclContext *DC,
                                     TypeSourceInfo *TInfo,
                                     LookupResult &Previous);
 
   /// ActOnTypedefNameDecl - Perform semantic checking for a declaration which
   /// declares a typedef-name, either using the 'typedef' type specifier or via
   /// a C++0x [dcl.typedef]p2 alias-declaration: 'using T = A;'.
   NamedDecl *ActOnTypedefNameDecl(Scope *S, DeclContext *DC, TypedefNameDecl *D,
                                   LookupResult &Previous, bool &Redeclaration);
   NamedDecl *ActOnVariableDeclarator(Scope *S, Declarator &D, DeclContext *DC,
                                      TypeSourceInfo *TInfo,
                                      LookupResult &Previous,
                                      MultiTemplateParamsArg TemplateParamLists,
                                      bool &AddToScope,
                                      ArrayRef<BindingDecl *> Bindings = {});
 
   /// Perform semantic checking on a newly-created variable
   /// declaration.
   ///
   /// This routine performs all of the type-checking required for a
   /// variable declaration once it has been built. It is used both to
   /// check variables after they have been parsed and their declarators
   /// have been translated into a declaration, and to check variables
   /// that have been instantiated from a template.
   ///
   /// Sets NewVD->isInvalidDecl() if an error was encountered.
   ///
   /// Returns true if the variable declaration is a redeclaration.
   bool CheckVariableDeclaration(VarDecl *NewVD, LookupResult &Previous);
   void CheckVariableDeclarationType(VarDecl *NewVD);
   void CheckCompleteVariableDeclaration(VarDecl *VD);
 
   NamedDecl *ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
                                      TypeSourceInfo *TInfo,
                                      LookupResult &Previous,
                                      MultiTemplateParamsArg TemplateParamLists,
                                      bool &AddToScope);
 
   /// AddOverriddenMethods - See if a method overrides any in the base classes,
   /// and if so, check that it's a valid override and remember it.
   bool AddOverriddenMethods(CXXRecordDecl *DC, CXXMethodDecl *MD);
 
   /// Perform semantic checking of a new function declaration.
   ///
   /// Performs semantic analysis of the new function declaration
   /// NewFD. This routine performs all semantic checking that does not
   /// require the actual declarator involved in the declaration, and is
   /// used both for the declaration of functions as they are parsed
   /// (called via ActOnDeclarator) and for the declaration of functions
   /// that have been instantiated via C++ template instantiation (called
   /// via InstantiateDecl).
   ///
   /// \param IsMemberSpecialization whether this new function declaration is
   /// a member specialization (that replaces any definition provided by the
   /// previous declaration).
   ///
   /// This sets NewFD->isInvalidDecl() to true if there was an error.
   ///
   /// \returns true if the function declaration is a redeclaration.
   bool CheckFunctionDeclaration(Scope *S, FunctionDecl *NewFD,
                                 LookupResult &Previous,
                                 bool IsMemberSpecialization, bool DeclIsDefn);
 
   /// Checks if the new declaration declared in dependent context must be
   /// put in the same redeclaration chain as the specified declaration.
   ///
   /// \param D Declaration that is checked.
   /// \param PrevDecl Previous declaration found with proper lookup method for
   ///                 the same declaration name.
   /// \returns True if D must be added to the redeclaration chain which PrevDecl
   ///          belongs to.
   bool shouldLinkDependentDeclWithPrevious(Decl *D, Decl *OldDecl);
 
   /// Determines if we can perform a correct type check for \p D as a
   /// redeclaration of \p PrevDecl. If not, we can generally still perform a
   /// best-effort check.
   ///
   /// \param NewD The new declaration.
   /// \param OldD The old declaration.
   /// \param NewT The portion of the type of the new declaration to check.
   /// \param OldT The portion of the type of the old declaration to check.
   bool canFullyTypeCheckRedeclaration(ValueDecl *NewD, ValueDecl *OldD,
                                       QualType NewT, QualType OldT);
   void CheckMain(FunctionDecl *FD, const DeclSpec &D);
   void CheckMSVCRTEntryPoint(FunctionDecl *FD);
 
   /// Returns an implicit CodeSegAttr if a __declspec(code_seg) is found on a
   /// containing class. Otherwise it will return implicit SectionAttr if the
   /// function is a definition and there is an active value on CodeSegStack
   /// (from the current #pragma code-seg value).
   ///
   /// \param FD Function being declared.
   /// \param IsDefinition Whether it is a definition or just a declaration.
   /// \returns A CodeSegAttr or SectionAttr to apply to the function or
   ///          nullptr if no attribute should be added.
   Attr *getImplicitCodeSegOrSectionAttrForFunction(const FunctionDecl *FD,
                                                    bool IsDefinition);
 
   /// Common checks for a parameter-declaration that should apply to both
   /// function parameters and non-type template parameters.
   void CheckFunctionOrTemplateParamDeclarator(Scope *S, Declarator &D);
 
   /// ActOnParamDeclarator - Called from Parser::ParseFunctionDeclarator()
   /// to introduce parameters into function prototype scope.
   Decl *ActOnParamDeclarator(Scope *S, Declarator &D,
                              SourceLocation ExplicitThisLoc = {});
 
   /// Synthesizes a variable for a parameter arising from a
   /// typedef.
   ParmVarDecl *BuildParmVarDeclForTypedef(DeclContext *DC, SourceLocation Loc,
                                           QualType T);
   ParmVarDecl *CheckParameter(DeclContext *DC, SourceLocation StartLoc,
                               SourceLocation NameLoc,
                               const IdentifierInfo *Name, QualType T,
                               TypeSourceInfo *TSInfo, StorageClass SC);
 
   // Contexts where using non-trivial C union types can be disallowed. This is
   // passed to err_non_trivial_c_union_in_invalid_context.
   enum NonTrivialCUnionContext {
     // Function parameter.
     NTCUC_FunctionParam,
     // Function return.
     NTCUC_FunctionReturn,
     // Default-initialized object.
     NTCUC_DefaultInitializedObject,
     // Variable with automatic storage duration.
     NTCUC_AutoVar,
     // Initializer expression that might copy from another object.
     NTCUC_CopyInit,
     // Assignment.
     NTCUC_Assignment,
     // Compound literal.
     NTCUC_CompoundLiteral,
     // Block capture.
     NTCUC_BlockCapture,
     // lvalue-to-rvalue conversion of volatile type.
     NTCUC_LValueToRValueVolatile,
   };
 
   /// Emit diagnostics if the initializer or any of its explicit or
   /// implicitly-generated subexpressions require copying or
   /// default-initializing a type that is or contains a C union type that is
   /// non-trivial to copy or default-initialize.
   void checkNonTrivialCUnionInInitializer(const Expr *Init, SourceLocation Loc);
 
   // These flags are passed to checkNonTrivialCUnion.
   enum NonTrivialCUnionKind {
     NTCUK_Init = 0x1,
     NTCUK_Destruct = 0x2,
     NTCUK_Copy = 0x4,
   };
 
   /// Emit diagnostics if a non-trivial C union type or a struct that contains
   /// a non-trivial C union is used in an invalid context.
   void checkNonTrivialCUnion(QualType QT, SourceLocation Loc,
                              NonTrivialCUnionContext UseContext,
                              unsigned NonTrivialKind);
 
   /// AddInitializerToDecl - Adds the initializer Init to the
   /// declaration dcl. If DirectInit is true, this is C++ direct
   /// initialization rather than copy initialization.
   void AddInitializerToDecl(Decl *dcl, Expr *init, bool DirectInit);
   void ActOnUninitializedDecl(Decl *dcl);
 
   /// ActOnInitializerError - Given that there was an error parsing an
   /// initializer for the given declaration, try to at least re-establish
   /// invariants such as whether a variable's type is either dependent or
   /// complete.
   void ActOnInitializerError(Decl *Dcl);
 
   void ActOnCXXForRangeDecl(Decl *D);
   StmtResult ActOnCXXForRangeIdentifier(Scope *S, SourceLocation IdentLoc,
                                         IdentifierInfo *Ident,
                                         ParsedAttributes &Attrs);
 
   /// Check if VD needs to be dllexport/dllimport due to being in a
   /// dllexport/import function.
   void CheckStaticLocalForDllExport(VarDecl *VD);
   void CheckThreadLocalForLargeAlignment(VarDecl *VD);
 
   /// FinalizeDeclaration - called by ParseDeclarationAfterDeclarator to perform
   /// any semantic actions necessary after any initializer has been attached.
   void FinalizeDeclaration(Decl *D);
   DeclGroupPtrTy FinalizeDeclaratorGroup(Scope *S, const DeclSpec &DS,
                                          ArrayRef<Decl *> Group);
 
   /// BuildDeclaratorGroup - convert a list of declarations into a declaration
   /// group, performing any necessary semantic checking.
   DeclGroupPtrTy BuildDeclaratorGroup(MutableArrayRef<Decl *> Group);
 
   /// Should be called on all declarations that might have attached
   /// documentation comments.
   void ActOnDocumentableDecl(Decl *D);
   void ActOnDocumentableDecls(ArrayRef<Decl *> Group);
 
   enum class FnBodyKind {
     /// C++26 [dcl.fct.def.general]p1
     /// function-body:
     ///   ctor-initializer[opt] compound-statement
     ///   function-try-block
     Other,
     ///   = default ;
     Default,
     ///   deleted-function-body
     ///
     /// deleted-function-body:
     ///   = delete ;
     ///   = delete ( unevaluated-string ) ;
     Delete
   };
 
   void ActOnFinishKNRParamDeclarations(Scope *S, Declarator &D,
                                        SourceLocation LocAfterDecls);
   void CheckForFunctionRedefinition(
       FunctionDecl *FD, const FunctionDecl *EffectiveDefinition = nullptr,
       SkipBodyInfo *SkipBody = nullptr);
   Decl *ActOnStartOfFunctionDef(Scope *S, Declarator &D,
                                 MultiTemplateParamsArg TemplateParamLists,
                                 SkipBodyInfo *SkipBody = nullptr,
                                 FnBodyKind BodyKind = FnBodyKind::Other);
   Decl *ActOnStartOfFunctionDef(Scope *S, Decl *D,
                                 SkipBodyInfo *SkipBody = nullptr,
                                 FnBodyKind BodyKind = FnBodyKind::Other);
   void applyFunctionAttributesBeforeParsingBody(Decl *FD);
 
   /// Determine whether we can delay parsing the body of a function or
   /// function template until it is used, assuming we don't care about emitting
   /// code for that function.
   ///
   /// This will be \c false if we may need the body of the function in the
   /// middle of parsing an expression (where it's impractical to switch to
   /// parsing a different function), for instance, if it's constexpr in C++11
   /// or has an 'auto' return type in C++14. These cases are essentially bugs.
   bool canDelayFunctionBody(const Declarator &D);
 
   /// Determine whether we can skip parsing the body of a function
   /// definition, assuming we don't care about analyzing its body or emitting
   /// code for that function.
   ///
   /// This will be \c false only if we may need the body of the function in
   /// order to parse the rest of the program (for instance, if it is
   /// \c constexpr in C++11 or has an 'auto' return type in C++14).
   bool canSkipFunctionBody(Decl *D);
 
   /// Given the set of return statements within a function body,
   /// compute the variables that are subject to the named return value
   /// optimization.
   ///
   /// Each of the variables that is subject to the named return value
   /// optimization will be marked as NRVO variables in the AST, and any
   /// return statement that has a marked NRVO variable as its NRVO candidate can
   /// use the named return value optimization.
   ///
   /// This function applies a very simplistic algorithm for NRVO: if every
   /// return statement in the scope of a variable has the same NRVO candidate,
   /// that candidate is an NRVO variable.
   void computeNRVO(Stmt *Body, sema::FunctionScopeInfo *Scope);
   Decl *ActOnFinishFunctionBody(Decl *Decl, Stmt *Body);
   Decl *ActOnFinishFunctionBody(Decl *Decl, Stmt *Body, bool IsInstantiation);
   Decl *ActOnSkippedFunctionBody(Decl *Decl);
   void ActOnFinishInlineFunctionDef(FunctionDecl *D);
 
   /// ActOnFinishDelayedAttribute - Invoked when we have finished parsing an
   /// attribute for which parsing is delayed.
   void ActOnFinishDelayedAttribute(Scope *S, Decl *D, ParsedAttributes &Attrs);
 
   /// Diagnose any unused parameters in the given sequence of
   /// ParmVarDecl pointers.
   void DiagnoseUnusedParameters(ArrayRef<ParmVarDecl *> Parameters);
 
   /// Diagnose whether the size of parameters or return value of a
   /// function or obj-c method definition is pass-by-value and larger than a
   /// specified threshold.
   void
   DiagnoseSizeOfParametersAndReturnValue(ArrayRef<ParmVarDecl *> Parameters,
                                          QualType ReturnTy, NamedDecl *D);
 
   Decl *ActOnFileScopeAsmDecl(Expr *expr, SourceLocation AsmLoc,
                               SourceLocation RParenLoc);
 
   TopLevelStmtDecl *ActOnStartTopLevelStmtDecl(Scope *S);
   void ActOnFinishTopLevelStmtDecl(TopLevelStmtDecl *D, Stmt *Statement);
 
   void ActOnPopScope(SourceLocation Loc, Scope *S);
 
   /// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
   /// no declarator (e.g. "struct foo;") is parsed.
   Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                    const ParsedAttributesView &DeclAttrs,
                                    RecordDecl *&AnonRecord);
 
   /// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
   /// no declarator (e.g. "struct foo;") is parsed. It also accepts template
   /// parameters to cope with template friend declarations.
   Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                    const ParsedAttributesView &DeclAttrs,
                                    MultiTemplateParamsArg TemplateParams,
                                    bool IsExplicitInstantiation,
                                    RecordDecl *&AnonRecord,
                                    SourceLocation EllipsisLoc = {});
 
   /// BuildAnonymousStructOrUnion - Handle the declaration of an
   /// anonymous structure or union. Anonymous unions are a C++ feature
   /// (C++ [class.union]) and a C11 feature; anonymous structures
   /// are a C11 feature and GNU C++ extension.
   Decl *BuildAnonymousStructOrUnion(Scope *S, DeclSpec &DS, AccessSpecifier AS,
                                     RecordDecl *Record,
                                     const PrintingPolicy &Policy);
 
   /// Called once it is known whether
   /// a tag declaration is an anonymous union or struct.
   void ActOnDefinedDeclarationSpecifier(Decl *D);
 
   /// Emit diagnostic warnings for placeholder members.
   /// We can only do that after the class is fully constructed,
   /// as anonymous union/structs can insert placeholders
   /// in their parent scope (which might be a Record).
   void DiagPlaceholderFieldDeclDefinitions(RecordDecl *Record);
 
   /// BuildMicrosoftCAnonymousStruct - Handle the declaration of an
   /// Microsoft C anonymous structure.
   /// Ref: http://msdn.microsoft.com/en-us/library/z2cx9y4f.aspx
   /// Example:
   ///
   /// struct A { int a; };
   /// struct B { struct A; int b; };
   ///
   /// void foo() {
   ///   B var;
   ///   var.a = 3;
   /// }
   Decl *BuildMicrosoftCAnonymousStruct(Scope *S, DeclSpec &DS,
                                        RecordDecl *Record);
 
   /// Common ways to introduce type names without a tag for use in diagnostics.
   /// Keep in sync with err_tag_reference_non_tag.
   enum NonTagKind {
     NTK_NonStruct,
     NTK_NonClass,
     NTK_NonUnion,
     NTK_NonEnum,
     NTK_Typedef,
     NTK_TypeAlias,
     NTK_Template,
     NTK_TypeAliasTemplate,
     NTK_TemplateTemplateArgument,
   };
 
   /// Given a non-tag type declaration, returns an enum useful for indicating
   /// what kind of non-tag type this is.
   NonTagKind getNonTagTypeDeclKind(const Decl *D, TagTypeKind TTK);
 
   /// Determine whether a tag with a given kind is acceptable
   /// as a redeclaration of the given tag declaration.
   ///
   /// \returns true if the new tag kind is acceptable, false otherwise.
   bool isAcceptableTagRedeclaration(const TagDecl *Previous, TagTypeKind NewTag,
                                     bool isDefinition, SourceLocation NewTagLoc,
                                     const IdentifierInfo *Name);
 
   enum OffsetOfKind {
     // Not parsing a type within __builtin_offsetof.
     OOK_Outside,
     // Parsing a type within __builtin_offsetof.
     OOK_Builtin,
     // Parsing a type within macro "offsetof", defined in __buitin_offsetof
     // To improve our diagnostic message.
     OOK_Macro,
   };
 
   /// This is invoked when we see 'struct foo' or 'struct {'.  In the
   /// former case, Name will be non-null.  In the later case, Name will be null.
   /// TagSpec indicates what kind of tag this is. TUK indicates whether this is
   /// a reference/declaration/definition of a tag.
   ///
   /// \param IsTypeSpecifier \c true if this is a type-specifier (or
   /// trailing-type-specifier) other than one in an alias-declaration.
   ///
   /// \param SkipBody If non-null, will be set to indicate if the caller should
   /// skip the definition of this tag and treat it as if it were a declaration.
   DeclResult ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                       SourceLocation KWLoc, CXXScopeSpec &SS,
                       IdentifierInfo *Name, SourceLocation NameLoc,
                       const ParsedAttributesView &Attr, AccessSpecifier AS,
                       SourceLocation ModulePrivateLoc,
                       MultiTemplateParamsArg TemplateParameterLists,
                       bool &OwnedDecl, bool &IsDependent,
                       SourceLocation ScopedEnumKWLoc,
                       bool ScopedEnumUsesClassTag, TypeResult UnderlyingType,
                       bool IsTypeSpecifier, bool IsTemplateParamOrArg,
                       OffsetOfKind OOK, SkipBodyInfo *SkipBody = nullptr);
 
   /// ActOnField - Each field of a C struct/union is passed into this in order
   /// to create a FieldDecl object for it.
   Decl *ActOnField(Scope *S, Decl *TagD, SourceLocation DeclStart,
                    Declarator &D, Expr *BitfieldWidth);
 
   /// HandleField - Analyze a field of a C struct or a C++ data member.
   FieldDecl *HandleField(Scope *S, RecordDecl *TagD, SourceLocation DeclStart,
                          Declarator &D, Expr *BitfieldWidth,
                          InClassInitStyle InitStyle, AccessSpecifier AS);
 
   /// Build a new FieldDecl and check its well-formedness.
   ///
   /// This routine builds a new FieldDecl given the fields name, type,
   /// record, etc. \p PrevDecl should refer to any previous declaration
   /// with the same name and in the same scope as the field to be
   /// created.
   ///
   /// \returns a new FieldDecl.
   ///
   /// \todo The Declarator argument is a hack. It will be removed once
   FieldDecl *CheckFieldDecl(DeclarationName Name, QualType T,
                             TypeSourceInfo *TInfo, RecordDecl *Record,
                             SourceLocation Loc, bool Mutable,
                             Expr *BitfieldWidth, InClassInitStyle InitStyle,
                             SourceLocation TSSL, AccessSpecifier AS,
                             NamedDecl *PrevDecl, Declarator *D = nullptr);
 
   bool CheckNontrivialField(FieldDecl *FD);
 
   /// ActOnLastBitfield - This routine handles synthesized bitfields rules for
   /// class and class extensions. For every class \@interface and class
   /// extension \@interface, if the last ivar is a bitfield of any type,
   /// then add an implicit `char :0` ivar to the end of that interface.
   void ActOnLastBitfield(SourceLocation DeclStart,
                          SmallVectorImpl<Decl *> &AllIvarDecls);
 
   // This is used for both record definitions and ObjC interface declarations.
   void ActOnFields(Scope *S, SourceLocation RecLoc, Decl *TagDecl,
                    ArrayRef<Decl *> Fields, SourceLocation LBrac,
                    SourceLocation RBrac, const ParsedAttributesView &AttrList);
 
   /// ActOnTagStartDefinition - Invoked when we have entered the
   /// scope of a tag's definition (e.g., for an enumeration, class,
   /// struct, or union).
   void ActOnTagStartDefinition(Scope *S, Decl *TagDecl);
 
   /// Perform ODR-like check for C/ObjC when merging tag types from modules.
   /// Differently from C++, actually parse the body and reject / error out
   /// in case of a structural mismatch.
   bool ActOnDuplicateDefinition(Decl *Prev, SkipBodyInfo &SkipBody);
 
   typedef void *SkippedDefinitionContext;
 
   /// Invoked when we enter a tag definition that we're skipping.
   SkippedDefinitionContext ActOnTagStartSkippedDefinition(Scope *S, Decl *TD);
 
   /// ActOnStartCXXMemberDeclarations - Invoked when we have parsed a
   /// C++ record definition's base-specifiers clause and are starting its
   /// member declarations.
   void ActOnStartCXXMemberDeclarations(Scope *S, Decl *TagDecl,
                                        SourceLocation FinalLoc,
                                        bool IsFinalSpelledSealed,
                                        bool IsAbstract,
                                        SourceLocation LBraceLoc);
 
   /// ActOnTagFinishDefinition - Invoked once we have finished parsing
   /// the definition of a tag (enumeration, class, struct, or union).
   void ActOnTagFinishDefinition(Scope *S, Decl *TagDecl,
                                 SourceRange BraceRange);
 
   void ActOnTagFinishSkippedDefinition(SkippedDefinitionContext Context);
 
   /// ActOnTagDefinitionError - Invoked when there was an unrecoverable
   /// error parsing the definition of a tag.
   void ActOnTagDefinitionError(Scope *S, Decl *TagDecl);
 
   EnumConstantDecl *CheckEnumConstant(EnumDecl *Enum,
                                       EnumConstantDecl *LastEnumConst,
                                       SourceLocation IdLoc, IdentifierInfo *Id,
                                       Expr *val);
 
   /// Check that this is a valid underlying type for an enum declaration.
   bool CheckEnumUnderlyingType(TypeSourceInfo *TI);
 
   /// Check whether this is a valid redeclaration of a previous enumeration.
   /// \return true if the redeclaration was invalid.
   bool CheckEnumRedeclaration(SourceLocation EnumLoc, bool IsScoped,
                               QualType EnumUnderlyingTy, bool IsFixed,
                               const EnumDecl *Prev);
 
   /// Determine whether the body of an anonymous enumeration should be skipped.
   /// \param II The name of the first enumerator.
   SkipBodyInfo shouldSkipAnonEnumBody(Scope *S, IdentifierInfo *II,
                                       SourceLocation IILoc);
 
   Decl *ActOnEnumConstant(Scope *S, Decl *EnumDecl, Decl *LastEnumConstant,
                           SourceLocation IdLoc, IdentifierInfo *Id,
                           const ParsedAttributesView &Attrs,
                           SourceLocation EqualLoc, Expr *Val);
   void ActOnEnumBody(SourceLocation EnumLoc, SourceRange BraceRange,
                      Decl *EnumDecl, ArrayRef<Decl *> Elements, Scope *S,
                      const ParsedAttributesView &Attr);
 
   /// Set the current declaration context until it gets popped.
   void PushDeclContext(Scope *S, DeclContext *DC);
   void PopDeclContext();
 
   /// EnterDeclaratorContext - Used when we must lookup names in the context
   /// of a declarator's nested name specifier.
   void EnterDeclaratorContext(Scope *S, DeclContext *DC);
   void ExitDeclaratorContext(Scope *S);
 
   /// Enter a template parameter scope, after it's been associated with a
   /// particular DeclContext. Causes lookup within the scope to chain through
   /// enclosing contexts in the correct order.
   void EnterTemplatedContext(Scope *S, DeclContext *DC);
 
   /// Push the parameters of D, which must be a function, into scope.
   void ActOnReenterFunctionContext(Scope *S, Decl *D);
   void ActOnExitFunctionContext();
 
   /// Add this decl to the scope shadowed decl chains.
   void PushOnScopeChains(NamedDecl *D, Scope *S, bool AddToContext = true);
 
   /// isDeclInScope - If 'Ctx' is a function/method, isDeclInScope returns true
   /// if 'D' is in Scope 'S', otherwise 'S' is ignored and isDeclInScope returns
   /// true if 'D' belongs to the given declaration context.
   ///
   /// \param AllowInlineNamespace If \c true, allow the declaration to be in the
   ///        enclosing namespace set of the context, rather than contained
   ///        directly within it.
   bool isDeclInScope(NamedDecl *D, DeclContext *Ctx, Scope *S = nullptr,
                      bool AllowInlineNamespace = false) const;
 
   /// Finds the scope corresponding to the given decl context, if it
   /// happens to be an enclosing scope.  Otherwise return NULL.
   static Scope *getScopeForDeclContext(Scope *S, DeclContext *DC);
 
   /// Subroutines of ActOnDeclarator().
   TypedefDecl *ParseTypedefDecl(Scope *S, Declarator &D, QualType T,
                                 TypeSourceInfo *TInfo);
   bool isIncompatibleTypedef(const TypeDecl *Old, TypedefNameDecl *New);
 
   /// Describes the kind of merge to perform for availability
   /// attributes (including "deprecated", "unavailable", and "availability").
   enum AvailabilityMergeKind {
     /// Don't merge availability attributes at all.
     AMK_None,
     /// Merge availability attributes for a redeclaration, which requires
     /// an exact match.
     AMK_Redeclaration,
     /// Merge availability attributes for an override, which requires
     /// an exact match or a weakening of constraints.
     AMK_Override,
     /// Merge availability attributes for an implementation of
     /// a protocol requirement.
     AMK_ProtocolImplementation,
     /// Merge availability attributes for an implementation of
     /// an optional protocol requirement.
     AMK_OptionalProtocolImplementation
   };
 
   /// mergeDeclAttributes - Copy attributes from the Old decl to the New one.
   void mergeDeclAttributes(NamedDecl *New, Decl *Old,
                            AvailabilityMergeKind AMK = AMK_Redeclaration);
 
   /// MergeTypedefNameDecl - We just parsed a typedef 'New' which has the
   /// same name and scope as a previous declaration 'Old'.  Figure out
   /// how to resolve this situation, merging decls or emitting
   /// diagnostics as appropriate. If there was an error, set New to be invalid.
   void MergeTypedefNameDecl(Scope *S, TypedefNameDecl *New,
                             LookupResult &OldDecls);
 
   /// MergeFunctionDecl - We just parsed a function 'New' from
   /// declarator D which has the same name and scope as a previous
   /// declaration 'Old'.  Figure out how to resolve this situation,
   /// merging decls or emitting diagnostics as appropriate.
   ///
   /// In C++, New and Old must be declarations that are not
   /// overloaded. Use IsOverload to determine whether New and Old are
   /// overloaded, and to select the Old declaration that New should be
   /// merged with.
   ///
   /// Returns true if there was an error, false otherwise.
   bool MergeFunctionDecl(FunctionDecl *New, NamedDecl *&Old, Scope *S,
                          bool MergeTypeWithOld, bool NewDeclIsDefn);
 
   /// Completes the merge of two function declarations that are
   /// known to be compatible.
   ///
   /// This routine handles the merging of attributes and other
   /// properties of function declarations from the old declaration to
   /// the new declaration, once we know that New is in fact a
   /// redeclaration of Old.
   ///
   /// \returns false
   bool MergeCompatibleFunctionDecls(FunctionDecl *New, FunctionDecl *Old,
                                     Scope *S, bool MergeTypeWithOld);
   void mergeObjCMethodDecls(ObjCMethodDecl *New, ObjCMethodDecl *Old);
 
   /// MergeVarDecl - We just parsed a variable 'New' which has the same name
   /// and scope as a previous declaration 'Old'.  Figure out how to resolve this
   /// situation, merging decls or emitting diagnostics as appropriate.
   ///
   /// Tentative definition rules (C99 6.9.2p2) are checked by
   /// FinalizeDeclaratorGroup. Unfortunately, we can't analyze tentative
   /// definitions here, since the initializer hasn't been attached.
   void MergeVarDecl(VarDecl *New, LookupResult &Previous);
 
   /// MergeVarDeclTypes - We parsed a variable 'New' which has the same name and
   /// scope as a previous declaration 'Old'.  Figure out how to merge their
   /// types, emitting diagnostics as appropriate.
   ///
   /// Declarations using the auto type specifier (C++ [decl.spec.auto]) call
   /// back to here in AddInitializerToDecl. We can't check them before the
   /// initializer is attached.
   void MergeVarDeclTypes(VarDecl *New, VarDecl *Old, bool MergeTypeWithOld);
 
   /// We've just determined that \p Old and \p New both appear to be definitions
   /// of the same variable. Either diagnose or fix the problem.
   bool checkVarDeclRedefinition(VarDecl *OldDefn, VarDecl *NewDefn);
   void notePreviousDefinition(const NamedDecl *Old, SourceLocation New);
 
   /// Filters out lookup results that don't fall within the given scope
   /// as determined by isDeclInScope.
   void FilterLookupForScope(LookupResult &R, DeclContext *Ctx, Scope *S,
                             bool ConsiderLinkage, bool AllowInlineNamespace);
 
   /// We've determined that \p New is a redeclaration of \p Old. Check that they
   /// have compatible owning modules.
   bool CheckRedeclarationModuleOwnership(NamedDecl *New, NamedDecl *Old);
 
   /// [module.interface]p6:
   /// A redeclaration of an entity X is implicitly exported if X was introduced
   /// by an exported declaration; otherwise it shall not be exported.
   bool CheckRedeclarationExported(NamedDecl *New, NamedDecl *Old);
 
   /// A wrapper function for checking the semantic restrictions of
   /// a redeclaration within a module.
   bool CheckRedeclarationInModule(NamedDecl *New, NamedDecl *Old);
 
   /// Check the redefinition in C++20 Modules.
   ///
   /// [basic.def.odr]p14:
   /// For any definable item D with definitions in multiple translation units,
   /// - if D is a non-inline non-templated function or variable, or
   /// - if the definitions in different translation units do not satisfy the
   /// following requirements,
   ///   the program is ill-formed; a diagnostic is required only if the
   ///   definable item is attached to a named module and a prior definition is
   ///   reachable at the point where a later definition occurs.
   /// - Each such definition shall not be attached to a named module
   /// ([module.unit]).
   /// - Each such definition shall consist of the same sequence of tokens, ...
   /// ...
   ///
   /// Return true if the redefinition is not allowed. Return false otherwise.
   bool IsRedefinitionInModule(const NamedDecl *New, const NamedDecl *Old) const;
 
   bool ShouldWarnIfUnusedFileScopedDecl(const DeclaratorDecl *D) const;
 
   /// If it's a file scoped decl that must warn if not used, keep track
   /// of it.
   void MarkUnusedFileScopedDecl(const DeclaratorDecl *D);
 
   typedef llvm::function_ref<void(SourceLocation Loc, PartialDiagnostic PD)>
       DiagReceiverTy;
 
   void DiagnoseUnusedNestedTypedefs(const RecordDecl *D);
   void DiagnoseUnusedNestedTypedefs(const RecordDecl *D,
                                     DiagReceiverTy DiagReceiver);
   void DiagnoseUnusedDecl(const NamedDecl *ND);
 
   /// DiagnoseUnusedDecl - Emit warnings about declarations that are not used
   /// unless they are marked attr(unused).
   void DiagnoseUnusedDecl(const NamedDecl *ND, DiagReceiverTy DiagReceiver);
 
   /// If VD is set but not otherwise used, diagnose, for a parameter or a
   /// variable.
   void DiagnoseUnusedButSetDecl(const VarDecl *VD, DiagReceiverTy DiagReceiver);
 
   /// getNonFieldDeclScope - Retrieves the innermost scope, starting
   /// from S, where a non-field would be declared. This routine copes
   /// with the difference between C and C++ scoping rules in structs and
   /// unions. For example, the following code is well-formed in C but
   /// ill-formed in C++:
   /// @code
   /// struct S6 {
   ///   enum { BAR } e;
   /// };
   ///
   /// void test_S6() {
   ///   struct S6 a;
   ///   a.e = BAR;
   /// }
   /// @endcode
   /// For the declaration of BAR, this routine will return a different
   /// scope. The scope S will be the scope of the unnamed enumeration
   /// within S6. In C++, this routine will return the scope associated
   /// with S6, because the enumeration's scope is a transparent
   /// context but structures can contain non-field names. In C, this
   /// routine will return the translation unit scope, since the
   /// enumeration's scope is a transparent context and structures cannot
   /// contain non-field names.
   Scope *getNonFieldDeclScope(Scope *S);
 
   FunctionDecl *CreateBuiltin(IdentifierInfo *II, QualType Type, unsigned ID,
                               SourceLocation Loc);
 
   /// LazilyCreateBuiltin - The specified Builtin-ID was first used at
   /// file scope.  lazily create a decl for it. ForRedeclaration is true
   /// if we're creating this built-in in anticipation of redeclaring the
   /// built-in.
   NamedDecl *LazilyCreateBuiltin(IdentifierInfo *II, unsigned ID, Scope *S,
                                  bool ForRedeclaration, SourceLocation Loc);
 
   /// Get the outermost AttributedType node that sets a calling convention.
   /// Valid types should not have multiple attributes with different CCs.
   const AttributedType *getCallingConvAttributedType(QualType T) const;
 
   /// GetNameForDeclarator - Determine the full declaration name for the
   /// given Declarator.
   DeclarationNameInfo GetNameForDeclarator(Declarator &D);
 
   /// Retrieves the declaration name from a parsed unqualified-id.
   DeclarationNameInfo GetNameFromUnqualifiedId(const UnqualifiedId &Name);
 
   /// ParsingInitForAutoVars - a set of declarations with auto types for which
   /// we are currently parsing the initializer.
   llvm::SmallPtrSet<const Decl *, 4> ParsingInitForAutoVars;
 
   /// Look for a locally scoped extern "C" declaration by the given name.
   NamedDecl *findLocallyScopedExternCDecl(DeclarationName Name);
 
   void deduceOpenCLAddressSpace(ValueDecl *decl);
 
   /// Adjust the \c DeclContext for a function or variable that might be a
   /// function-local external declaration.
   static bool adjustContextForLocalExternDecl(DeclContext *&DC);
 
   void MarkTypoCorrectedFunctionDefinition(const NamedDecl *F);
 
   /// Checks if the variant/multiversion functions are compatible.
   bool areMultiversionVariantFunctionsCompatible(
       const FunctionDecl *OldFD, const FunctionDecl *NewFD,
       const PartialDiagnostic &NoProtoDiagID,
       const PartialDiagnosticAt &NoteCausedDiagIDAt,
       const PartialDiagnosticAt &NoSupportDiagIDAt,
       const PartialDiagnosticAt &DiffDiagIDAt, bool TemplatesSupported,
       bool ConstexprSupported, bool CLinkageMayDiffer);
 
   /// type checking declaration initializers (C99 6.7.8)
   bool CheckForConstantInitializer(
       Expr *Init, unsigned DiagID = diag::err_init_element_not_constant);
 
   QualType deduceVarTypeFromInitializer(VarDecl *VDecl, DeclarationName Name,
                                         QualType Type, TypeSourceInfo *TSI,
                                         SourceRange Range, bool DirectInit,
                                         Expr *Init);
 
   bool DeduceVariableDeclarationType(VarDecl *VDecl, bool DirectInit,
                                      Expr *Init);
 
   sema::LambdaScopeInfo *RebuildLambdaScopeInfo(CXXMethodDecl *CallOperator);
 
   // Heuristically tells if the function is `get_return_object` member of a
   // coroutine promise_type by matching the function name.
   static bool CanBeGetReturnObject(const FunctionDecl *FD);
   static bool CanBeGetReturnTypeOnAllocFailure(const FunctionDecl *FD);
 
   /// ImplicitlyDefineFunction - An undeclared identifier was used in a function
   /// call, forming a call to an implicitly defined function (per C99 6.5.1p2).
   NamedDecl *ImplicitlyDefineFunction(SourceLocation Loc, IdentifierInfo &II,
                                       Scope *S);
 
   /// If this function is a C++ replaceable global allocation function
   /// (C++2a [basic.stc.dynamic.allocation], C++2a [new.delete]),
   /// adds any function attributes that we know a priori based on the standard.
   ///
   /// We need to check for duplicate attributes both here and where user-written
   /// attributes are applied to declarations.
   void AddKnownFunctionAttributesForReplaceableGlobalAllocationFunction(
       FunctionDecl *FD);
 
   /// Adds any function attributes that we know a priori based on
   /// the declaration of this function.
   ///
   /// These attributes can apply both to implicitly-declared builtins
   /// (like __builtin___printf_chk) or to library-declared functions
   /// like NSLog or printf.
   ///
   /// We need to check for duplicate attributes both here and where user-written
   /// attributes are applied to declarations.
   void AddKnownFunctionAttributes(FunctionDecl *FD);
 
   /// VerifyBitField - verifies that a bit field expression is an ICE and has
   /// the correct width, and that the field type is valid.
   /// Returns false on success.
   ExprResult VerifyBitField(SourceLocation FieldLoc,
                             const IdentifierInfo *FieldName, QualType FieldTy,
                             bool IsMsStruct, Expr *BitWidth);
 
   /// IsValueInFlagEnum - Determine if a value is allowed as part of a flag
   /// enum. If AllowMask is true, then we also allow the complement of a valid
   /// value, to be used as a mask.
   bool IsValueInFlagEnum(const EnumDecl *ED, const llvm::APInt &Val,
                          bool AllowMask) const;
 
   /// ActOnPragmaWeakID - Called on well formed \#pragma weak ident.
   void ActOnPragmaWeakID(IdentifierInfo *WeakName, SourceLocation PragmaLoc,
                          SourceLocation WeakNameLoc);
 
   /// ActOnPragmaRedefineExtname - Called on well formed
   /// \#pragma redefine_extname oldname newname.
   void ActOnPragmaRedefineExtname(IdentifierInfo *WeakName,
                                   IdentifierInfo *AliasName,
                                   SourceLocation PragmaLoc,
                                   SourceLocation WeakNameLoc,
                                   SourceLocation AliasNameLoc);
 
   /// ActOnPragmaWeakAlias - Called on well formed \#pragma weak ident = ident.
   void ActOnPragmaWeakAlias(IdentifierInfo *WeakName, IdentifierInfo *AliasName,
                             SourceLocation PragmaLoc,
                             SourceLocation WeakNameLoc,
                             SourceLocation AliasNameLoc);
 
   /// Status of the function emission on the CUDA/HIP/OpenMP host/device attrs.
   enum class FunctionEmissionStatus {
     Emitted,
     CUDADiscarded,     // Discarded due to CUDA/HIP hostness
     OMPDiscarded,      // Discarded due to OpenMP hostness
     TemplateDiscarded, // Discarded due to uninstantiated templates
     Unknown,
   };
   FunctionEmissionStatus getEmissionStatus(const FunctionDecl *Decl,
                                            bool Final = false);
 
   // Whether the callee should be ignored in CUDA/HIP/OpenMP host/device check.
   bool shouldIgnoreInHostDeviceCheck(FunctionDecl *Callee);
 
   /// Function or variable declarations to be checked for whether the deferred
   /// diagnostics should be emitted.
   llvm::SmallSetVector<Decl *, 4> DeclsToCheckForDeferredDiags;
 
 private:
   /// Map of current shadowing declarations to shadowed declarations. Warn if
   /// it looks like the user is trying to modify the shadowing declaration.
   llvm::DenseMap<const NamedDecl *, const NamedDecl *> ShadowingDecls;
 
   // We need this to handle
   //
   // typedef struct {
   //   void *foo() { return 0; }
   // } A;
   //
   // When we see foo we don't know if after the typedef we will get 'A' or '*A'
   // for example. If 'A', foo will have external linkage. If we have '*A',
   // foo will have no linkage. Since we can't know until we get to the end
   // of the typedef, this function finds out if D might have non-external
   // linkage. Callers should verify at the end of the TU if it D has external
   // linkage or not.
   static bool mightHaveNonExternalLinkage(const DeclaratorDecl *FD);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Declaration Attribute Handling
   /// Implementations are in SemaDeclAttr.cpp
   ///@{
 
 public:
   /// Describes the kind of priority given to an availability attribute.
   ///
   /// The sum of priorities deteremines the final priority of the attribute.
   /// The final priority determines how the attribute will be merged.
   /// An attribute with a lower priority will always remove higher priority
   /// attributes for the specified platform when it is being applied. An
   /// attribute with a higher priority will not be applied if the declaration
   /// already has an availability attribute with a lower priority for the
   /// specified platform. The final prirority values are not expected to match
   /// the values in this enumeration, but instead should be treated as a plain
   /// integer value. This enumeration just names the priority weights that are
   /// used to calculate that final vaue.
   enum AvailabilityPriority : int {
     /// The availability attribute was specified explicitly next to the
     /// declaration.
     AP_Explicit = 0,
 
     /// The availability attribute was applied using '#pragma clang attribute'.
     AP_PragmaClangAttribute = 1,
 
     /// The availability attribute for a specific platform was inferred from
     /// an availability attribute for another platform.
     AP_InferredFromOtherPlatform = 2
   };
 
   /// Describes the reason a calling convention specification was ignored, used
   /// for diagnostics.
   enum class CallingConventionIgnoredReason {
     ForThisTarget = 0,
     VariadicFunction,
     ConstructorDestructor,
     BuiltinFunction
   };
 
   /// A helper function to provide Attribute Location for the Attr types
   /// AND the ParsedAttr.
   template <typename AttrInfo>
   static std::enable_if_t<std::is_base_of_v<Attr, AttrInfo>, SourceLocation>
   getAttrLoc(const AttrInfo &AL) {
     return AL.getLocation();
   }
   SourceLocation getAttrLoc(const ParsedAttr &AL);
 
   /// If Expr is a valid integer constant, get the value of the integer
   /// expression and return success or failure. May output an error.
   ///
   /// Negative argument is implicitly converted to unsigned, unless
   /// \p StrictlyUnsigned is true.
   template <typename AttrInfo>
   bool checkUInt32Argument(const AttrInfo &AI, const Expr *Expr, uint32_t &Val,
                            unsigned Idx = UINT_MAX,
                            bool StrictlyUnsigned = false) {
     std::optional<llvm::APSInt> I = llvm::APSInt(32);
     if (Expr->isTypeDependent() ||
         !(I = Expr->getIntegerConstantExpr(Context))) {
       if (Idx != UINT_MAX)
         Diag(getAttrLoc(AI), diag::err_attribute_argument_n_type)
             << &AI << Idx << AANT_ArgumentIntegerConstant
             << Expr->getSourceRange();
       else
         Diag(getAttrLoc(AI), diag::err_attribute_argument_type)
             << &AI << AANT_ArgumentIntegerConstant << Expr->getSourceRange();
       return false;
     }
 
     if (!I->isIntN(32)) {
       Diag(Expr->getExprLoc(), diag::err_ice_too_large)
           << toString(*I, 10, false) << 32 << /* Unsigned */ 1;
       return false;
     }
 
     if (StrictlyUnsigned && I->isSigned() && I->isNegative()) {
       Diag(getAttrLoc(AI), diag::err_attribute_requires_positive_integer)
           << &AI << /*non-negative*/ 1;
       return false;
     }
 
     Val = (uint32_t)I->getZExtValue();
     return true;
   }
 
   /// WeakTopLevelDecl - Translation-unit scoped declarations generated by
   /// \#pragma weak during processing of other Decls.
   /// I couldn't figure out a clean way to generate these in-line, so
   /// we store them here and handle separately -- which is a hack.
   /// It would be best to refactor this.
   SmallVector<Decl *, 2> WeakTopLevelDecl;
 
   /// WeakTopLevelDeclDecls - access to \#pragma weak-generated Decls
   SmallVectorImpl<Decl *> &WeakTopLevelDecls() { return WeakTopLevelDecl; }
 
   typedef LazyVector<TypedefNameDecl *, ExternalSemaSource,
                      &ExternalSemaSource::ReadExtVectorDecls, 2, 2>
       ExtVectorDeclsType;
 
   /// ExtVectorDecls - This is a list all the extended vector types. This allows
   /// us to associate a raw vector type with one of the ext_vector type names.
   /// This is only necessary for issuing pretty diagnostics.
   ExtVectorDeclsType ExtVectorDecls;
 
   /// Check if the argument \p E is a ASCII string literal. If not emit an error
   /// and return false, otherwise set \p Str to the value of the string literal
   /// and return true.
   bool checkStringLiteralArgumentAttr(const AttributeCommonInfo &CI,
                                       const Expr *E, StringRef &Str,
                                       SourceLocation *ArgLocation = nullptr);
 
   /// Check if the argument \p ArgNum of \p Attr is a ASCII string literal.
   /// If not emit an error and return false. If the argument is an identifier it
   /// will emit an error with a fixit hint and treat it as if it was a string
   /// literal.
   bool checkStringLiteralArgumentAttr(const ParsedAttr &Attr, unsigned ArgNum,
                                       StringRef &Str,
                                       SourceLocation *ArgLocation = nullptr);
 
   /// Determine if type T is a valid subject for a nonnull and similar
   /// attributes. Dependent types are considered valid so they can be checked
   /// during instantiation time. By default, we look through references (the
   /// behavior used by nonnull), but if the second parameter is true, then we
   /// treat a reference type as valid.
   bool isValidPointerAttrType(QualType T, bool RefOkay = false);
 
   /// AddAssumeAlignedAttr - Adds an assume_aligned attribute to a particular
   /// declaration.
   void AddAssumeAlignedAttr(Decl *D, const AttributeCommonInfo &CI, Expr *E,
                             Expr *OE);
 
   /// AddAllocAlignAttr - Adds an alloc_align attribute to a particular
   /// declaration.
   void AddAllocAlignAttr(Decl *D, const AttributeCommonInfo &CI,
                          Expr *ParamExpr);
 
   bool CheckAttrTarget(const ParsedAttr &CurrAttr);
   bool CheckAttrNoArgs(const ParsedAttr &CurrAttr);
 
   AvailabilityAttr *mergeAvailabilityAttr(
       NamedDecl *D, const AttributeCommonInfo &CI, IdentifierInfo *Platform,
       bool Implicit, VersionTuple Introduced, VersionTuple Deprecated,
       VersionTuple Obsoleted, bool IsUnavailable, StringRef Message,
       bool IsStrict, StringRef Replacement, AvailabilityMergeKind AMK,
       int Priority, IdentifierInfo *IIEnvironment);
 
   TypeVisibilityAttr *
   mergeTypeVisibilityAttr(Decl *D, const AttributeCommonInfo &CI,
                           TypeVisibilityAttr::VisibilityType Vis);
   VisibilityAttr *mergeVisibilityAttr(Decl *D, const AttributeCommonInfo &CI,
                                       VisibilityAttr::VisibilityType Vis);
   SectionAttr *mergeSectionAttr(Decl *D, const AttributeCommonInfo &CI,
                                 StringRef Name);
 
   /// Used to implement to perform semantic checking on
   /// attribute((section("foo"))) specifiers.
   ///
   /// In this case, "foo" is passed in to be checked.  If the section
   /// specifier is invalid, return an Error that indicates the problem.
   ///
   /// This is a simple quality of implementation feature to catch errors
   /// and give good diagnostics in cases when the assembler or code generator
   /// would otherwise reject the section specifier.
   llvm::Error isValidSectionSpecifier(StringRef Str);
   bool checkSectionName(SourceLocation LiteralLoc, StringRef Str);
   CodeSegAttr *mergeCodeSegAttr(Decl *D, const AttributeCommonInfo &CI,
                                 StringRef Name);
 
   // Check for things we'd like to warn about. Multiversioning issues are
   // handled later in the process, once we know how many exist.
   bool checkTargetAttr(SourceLocation LiteralLoc, StringRef Str);
 
   /// Check Target Version attrs
   bool checkTargetVersionAttr(SourceLocation Loc, Decl *D, StringRef Str);
   bool checkTargetClonesAttrString(
       SourceLocation LiteralLoc, StringRef Str, const StringLiteral *Literal,
       Decl *D, bool &HasDefault, bool &HasCommas, bool &HasNotDefault,
       SmallVectorImpl<SmallString<64>> &StringsBuffer);
 
   ErrorAttr *mergeErrorAttr(Decl *D, const AttributeCommonInfo &CI,
                             StringRef NewUserDiagnostic);
   FormatAttr *mergeFormatAttr(Decl *D, const AttributeCommonInfo &CI,
                               IdentifierInfo *Format, int FormatIdx,
                               int FirstArg);
 
   /// AddAlignedAttr - Adds an aligned attribute to a particular declaration.
   void AddAlignedAttr(Decl *D, const AttributeCommonInfo &CI, Expr *E,
                       bool IsPackExpansion);
   void AddAlignedAttr(Decl *D, const AttributeCommonInfo &CI, TypeSourceInfo *T,
                       bool IsPackExpansion);
 
   /// AddAlignValueAttr - Adds an align_value attribute to a particular
   /// declaration.
   void AddAlignValueAttr(Decl *D, const AttributeCommonInfo &CI, Expr *E);
 
   /// CreateAnnotationAttr - Creates an annotation Annot with Args arguments.
   Attr *CreateAnnotationAttr(const AttributeCommonInfo &CI, StringRef Annot,
                              MutableArrayRef<Expr *> Args);
   Attr *CreateAnnotationAttr(const ParsedAttr &AL);
 
   bool checkMSInheritanceAttrOnDefinition(CXXRecordDecl *RD, SourceRange Range,
                                           bool BestCase,
                                           MSInheritanceModel SemanticSpelling);
 
   void CheckAlignasUnderalignment(Decl *D);
 
   /// AddModeAttr - Adds a mode attribute to a particular declaration.
   void AddModeAttr(Decl *D, const AttributeCommonInfo &CI, IdentifierInfo *Name,
                    bool InInstantiation = false);
   AlwaysInlineAttr *mergeAlwaysInlineAttr(Decl *D,
                                           const AttributeCommonInfo &CI,
                                           const IdentifierInfo *Ident);
   MinSizeAttr *mergeMinSizeAttr(Decl *D, const AttributeCommonInfo &CI);
   OptimizeNoneAttr *mergeOptimizeNoneAttr(Decl *D,
                                           const AttributeCommonInfo &CI);
   InternalLinkageAttr *mergeInternalLinkageAttr(Decl *D, const ParsedAttr &AL);
   InternalLinkageAttr *mergeInternalLinkageAttr(Decl *D,
                                                 const InternalLinkageAttr &AL);
 
   /// Check validaty of calling convention attribute \p attr. If \p FD
   /// is not null pointer, use \p FD to determine the CUDA/HIP host/device
   /// target. Otherwise, it is specified by \p CFT.
   bool CheckCallingConvAttr(
       const ParsedAttr &attr, CallingConv &CC, const FunctionDecl *FD = nullptr,
       CUDAFunctionTarget CFT = CUDAFunctionTarget::InvalidTarget);
 
   /// Checks a regparm attribute, returning true if it is ill-formed and
   /// otherwise setting numParams to the appropriate value.
   bool CheckRegparmAttr(const ParsedAttr &attr, unsigned &value);
 
   /// Create an CUDALaunchBoundsAttr attribute.
   CUDALaunchBoundsAttr *CreateLaunchBoundsAttr(const AttributeCommonInfo &CI,
                                                Expr *MaxThreads,
                                                Expr *MinBlocks,
                                                Expr *MaxBlocks);
 
   /// AddLaunchBoundsAttr - Adds a launch_bounds attribute to a particular
   /// declaration.
   void AddLaunchBoundsAttr(Decl *D, const AttributeCommonInfo &CI,
                            Expr *MaxThreads, Expr *MinBlocks, Expr *MaxBlocks);
 
   enum class RetainOwnershipKind { NS, CF, OS };
 
   UuidAttr *mergeUuidAttr(Decl *D, const AttributeCommonInfo &CI,
                           StringRef UuidAsWritten, MSGuidDecl *GuidDecl);
 
   BTFDeclTagAttr *mergeBTFDeclTagAttr(Decl *D, const BTFDeclTagAttr &AL);
 
   DLLImportAttr *mergeDLLImportAttr(Decl *D, const AttributeCommonInfo &CI);
   DLLExportAttr *mergeDLLExportAttr(Decl *D, const AttributeCommonInfo &CI);
   MSInheritanceAttr *mergeMSInheritanceAttr(Decl *D,
                                             const AttributeCommonInfo &CI,
                                             bool BestCase,
                                             MSInheritanceModel Model);
 
   EnforceTCBAttr *mergeEnforceTCBAttr(Decl *D, const EnforceTCBAttr &AL);
   EnforceTCBLeafAttr *mergeEnforceTCBLeafAttr(Decl *D,
                                               const EnforceTCBLeafAttr &AL);
 
   /// Helper for delayed processing TransparentUnion or
   /// BPFPreserveAccessIndexAttr attribute.
   void ProcessDeclAttributeDelayed(Decl *D,
                                    const ParsedAttributesView &AttrList);
 
   // Options for ProcessDeclAttributeList().
   struct ProcessDeclAttributeOptions {
     ProcessDeclAttributeOptions()
         : IncludeCXX11Attributes(true), IgnoreTypeAttributes(false) {}
 
     ProcessDeclAttributeOptions WithIncludeCXX11Attributes(bool Val) {
       ProcessDeclAttributeOptions Result = *this;
       Result.IncludeCXX11Attributes = Val;
       return Result;
     }
 
     ProcessDeclAttributeOptions WithIgnoreTypeAttributes(bool Val) {
       ProcessDeclAttributeOptions Result = *this;
       Result.IgnoreTypeAttributes = Val;
       return Result;
     }
 
     // Should C++11 attributes be processed?
     bool IncludeCXX11Attributes;
 
     // Should any type attributes encountered be ignored?
     // If this option is false, a diagnostic will be emitted for any type
     // attributes of a kind that does not "slide" from the declaration to
     // the decl-specifier-seq.
     bool IgnoreTypeAttributes;
   };
 
   /// ProcessDeclAttributeList - Apply all the decl attributes in the specified
   /// attribute list to the specified decl, ignoring any type attributes.
   void ProcessDeclAttributeList(Scope *S, Decl *D,
                                 const ParsedAttributesView &AttrList,
                                 const ProcessDeclAttributeOptions &Options =
                                     ProcessDeclAttributeOptions());
 
   /// Annotation attributes are the only attributes allowed after an access
   /// specifier.
   bool ProcessAccessDeclAttributeList(AccessSpecDecl *ASDecl,
                                       const ParsedAttributesView &AttrList);
 
   /// checkUnusedDeclAttributes - Given a declarator which is not being
   /// used to build a declaration, complain about any decl attributes
   /// which might be lying around on it.
   void checkUnusedDeclAttributes(Declarator &D);
 
   /// DeclClonePragmaWeak - clone existing decl (maybe definition),
   /// \#pragma weak needs a non-definition decl and source may not have one.
   NamedDecl *DeclClonePragmaWeak(NamedDecl *ND, const IdentifierInfo *II,
                                  SourceLocation Loc);
 
   /// DeclApplyPragmaWeak - A declaration (maybe definition) needs \#pragma weak
   /// applied to it, possibly with an alias.
   void DeclApplyPragmaWeak(Scope *S, NamedDecl *ND, const WeakInfo &W);
 
   void ProcessPragmaWeak(Scope *S, Decl *D);
   // Decl attributes - this routine is the top level dispatcher.
   void ProcessDeclAttributes(Scope *S, Decl *D, const Declarator &PD);
 
   void PopParsingDeclaration(ParsingDeclState state, Decl *decl);
 
   /// Given a set of delayed diagnostics, re-emit them as if they had
   /// been delayed in the current context instead of in the given pool.
   /// Essentially, this just moves them to the current pool.
   void redelayDiagnostics(sema::DelayedDiagnosticPool &pool);
 
   /// Check if IdxExpr is a valid parameter index for a function or
   /// instance method D.  May output an error.
   ///
   /// \returns true if IdxExpr is a valid index.
   template <typename AttrInfo>
   bool checkFunctionOrMethodParameterIndex(const Decl *D, const AttrInfo &AI,
                                            unsigned AttrArgNum,
                                            const Expr *IdxExpr, ParamIdx &Idx,
                                            bool CanIndexImplicitThis = false) {
     assert(isFunctionOrMethodOrBlockForAttrSubject(D));
 
     // In C++ the implicit 'this' function parameter also counts.
     // Parameters are counted from one.
     bool HP = hasFunctionProto(D);
     bool HasImplicitThisParam = isInstanceMethod(D);
     bool IV = HP && isFunctionOrMethodVariadic(D);
     unsigned NumParams =
         (HP ? getFunctionOrMethodNumParams(D) : 0) + HasImplicitThisParam;
 
     std::optional<llvm::APSInt> IdxInt;
     if (IdxExpr->isTypeDependent() ||
         !(IdxInt = IdxExpr->getIntegerConstantExpr(Context))) {
       Diag(getAttrLoc(AI), diag::err_attribute_argument_n_type)
           << &AI << AttrArgNum << AANT_ArgumentIntegerConstant
           << IdxExpr->getSourceRange();
       return false;
     }
 
     unsigned IdxSource = IdxInt->getLimitedValue(UINT_MAX);
     if (IdxSource < 1 || (!IV && IdxSource > NumParams)) {
       Diag(getAttrLoc(AI), diag::err_attribute_argument_out_of_bounds)
           << &AI << AttrArgNum << IdxExpr->getSourceRange();
       return false;
     }
     if (HasImplicitThisParam && !CanIndexImplicitThis) {
       if (IdxSource == 1) {
         Diag(getAttrLoc(AI), diag::err_attribute_invalid_implicit_this_argument)
             << &AI << IdxExpr->getSourceRange();
         return false;
       }
     }
 
     Idx = ParamIdx(IdxSource, D);
     return true;
   }
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Declarations
   /// Implementations are in SemaDeclCXX.cpp
   ///@{
 
 public:
   void CheckDelegatingCtorCycles();
 
   /// Called before parsing a function declarator belonging to a function
   /// declaration.
   void ActOnStartFunctionDeclarationDeclarator(Declarator &D,
                                                unsigned TemplateParameterDepth);
 
   /// Called after parsing a function declarator belonging to a function
   /// declaration.
   void ActOnFinishFunctionDeclarationDeclarator(Declarator &D);
 
   // Act on C++ namespaces
   Decl *ActOnStartNamespaceDef(Scope *S, SourceLocation InlineLoc,
                                SourceLocation NamespaceLoc,
                                SourceLocation IdentLoc, IdentifierInfo *Ident,
                                SourceLocation LBrace,
                                const ParsedAttributesView &AttrList,
                                UsingDirectiveDecl *&UsingDecl, bool IsNested);
 
   /// ActOnFinishNamespaceDef - This callback is called after a namespace is
   /// exited. Decl is the DeclTy returned by ActOnStartNamespaceDef.
   void ActOnFinishNamespaceDef(Decl *Dcl, SourceLocation RBrace);
 
   NamespaceDecl *getStdNamespace() const;
 
   /// Retrieve the special "std" namespace, which may require us to
   /// implicitly define the namespace.
   NamespaceDecl *getOrCreateStdNamespace();
 
   CXXRecordDecl *getStdBadAlloc() const;
   EnumDecl *getStdAlignValT() const;
 
   ValueDecl *tryLookupUnambiguousFieldDecl(RecordDecl *ClassDecl,
                                            const IdentifierInfo *MemberOrBase);
 
   enum class ComparisonCategoryUsage {
     /// The '<=>' operator was used in an expression and a builtin operator
     /// was selected.
     OperatorInExpression,
     /// A defaulted 'operator<=>' needed the comparison category. This
     /// typically only applies to 'std::strong_ordering', due to the implicit
     /// fallback return value.
     DefaultedOperator,
   };
 
   /// Lookup the specified comparison category types in the standard
   ///   library, an check the VarDecls possibly returned by the operator<=>
   ///   builtins for that type.
   ///
   /// \return The type of the comparison category type corresponding to the
   ///   specified Kind, or a null type if an error occurs
   QualType CheckComparisonCategoryType(ComparisonCategoryType Kind,
                                        SourceLocation Loc,
                                        ComparisonCategoryUsage Usage);
 
   /// Tests whether Ty is an instance of std::initializer_list and, if
   /// it is and Element is not NULL, assigns the element type to Element.
   bool isStdInitializerList(QualType Ty, QualType *Element);
 
   /// Looks for the std::initializer_list template and instantiates it
   /// with Element, or emits an error if it's not found.
   ///
   /// \returns The instantiated template, or null on error.
   QualType BuildStdInitializerList(QualType Element, SourceLocation Loc);
 
   /// Determine whether Ctor is an initializer-list constructor, as
   /// defined in [dcl.init.list]p2.
   bool isInitListConstructor(const FunctionDecl *Ctor);
 
   Decl *ActOnUsingDirective(Scope *CurScope, SourceLocation UsingLoc,
                             SourceLocation NamespcLoc, CXXScopeSpec &SS,
                             SourceLocation IdentLoc,
                             IdentifierInfo *NamespcName,
                             const ParsedAttributesView &AttrList);
 
   void PushUsingDirective(Scope *S, UsingDirectiveDecl *UDir);
 
   Decl *ActOnNamespaceAliasDef(Scope *CurScope, SourceLocation NamespaceLoc,
                                SourceLocation AliasLoc, IdentifierInfo *Alias,
                                CXXScopeSpec &SS, SourceLocation IdentLoc,
                                IdentifierInfo *Ident);
 
   /// Remove decls we can't actually see from a lookup being used to declare
   /// shadow using decls.
   ///
   /// \param S - The scope of the potential shadow decl
   /// \param Previous - The lookup of a potential shadow decl's name.
   void FilterUsingLookup(Scope *S, LookupResult &lookup);
 
   /// Hides a using shadow declaration.  This is required by the current
   /// using-decl implementation when a resolvable using declaration in a
   /// class is followed by a declaration which would hide or override
   /// one or more of the using decl's targets; for example:
   ///
   ///   struct Base { void foo(int); };
   ///   struct Derived : Base {
   ///     using Base::foo;
   ///     void foo(int);
   ///   };
   ///
   /// The governing language is C++03 [namespace.udecl]p12:
   ///
   ///   When a using-declaration brings names from a base class into a
   ///   derived class scope, member functions in the derived class
   ///   override and/or hide member functions with the same name and
   ///   parameter types in a base class (rather than conflicting).
   ///
   /// There are two ways to implement this:
   ///   (1) optimistically create shadow decls when they're not hidden
   ///       by existing declarations, or
   ///   (2) don't create any shadow decls (or at least don't make them
   ///       visible) until we've fully parsed/instantiated the class.
   /// The problem with (1) is that we might have to retroactively remove
   /// a shadow decl, which requires several O(n) operations because the
   /// decl structures are (very reasonably) not designed for removal.
   /// (2) avoids this but is very fiddly and phase-dependent.
   void HideUsingShadowDecl(Scope *S, UsingShadowDecl *Shadow);
 
   /// Determines whether to create a using shadow decl for a particular
   /// decl, given the set of decls existing prior to this using lookup.
   bool CheckUsingShadowDecl(BaseUsingDecl *BUD, NamedDecl *Target,
                             const LookupResult &PreviousDecls,
                             UsingShadowDecl *&PrevShadow);
 
   /// Builds a shadow declaration corresponding to a 'using' declaration.
   UsingShadowDecl *BuildUsingShadowDecl(Scope *S, BaseUsingDecl *BUD,
                                         NamedDecl *Target,
                                         UsingShadowDecl *PrevDecl);
 
   /// Checks that the given using declaration is not an invalid
   /// redeclaration.  Note that this is checking only for the using decl
   /// itself, not for any ill-formedness among the UsingShadowDecls.
   bool CheckUsingDeclRedeclaration(SourceLocation UsingLoc,
                                    bool HasTypenameKeyword,
                                    const CXXScopeSpec &SS,
                                    SourceLocation NameLoc,
                                    const LookupResult &Previous);
 
   /// Checks that the given nested-name qualifier used in a using decl
   /// in the current context is appropriately related to the current
   /// scope.  If an error is found, diagnoses it and returns true.
   /// R is nullptr, if the caller has not (yet) done a lookup, otherwise it's
   /// the result of that lookup. UD is likewise nullptr, except when we have an
   /// already-populated UsingDecl whose shadow decls contain the same
   /// information (i.e. we're instantiating a UsingDecl with non-dependent
   /// scope).
   bool CheckUsingDeclQualifier(SourceLocation UsingLoc, bool HasTypename,
                                const CXXScopeSpec &SS,
                                const DeclarationNameInfo &NameInfo,
                                SourceLocation NameLoc,
                                const LookupResult *R = nullptr,
                                const UsingDecl *UD = nullptr);
 
   /// Builds a using declaration.
   ///
   /// \param IsInstantiation - Whether this call arises from an
   ///   instantiation of an unresolved using declaration.  We treat
   ///   the lookup differently for these declarations.
   NamedDecl *BuildUsingDeclaration(Scope *S, AccessSpecifier AS,
                                    SourceLocation UsingLoc,
                                    bool HasTypenameKeyword,
                                    SourceLocation TypenameLoc, CXXScopeSpec &SS,
                                    DeclarationNameInfo NameInfo,
                                    SourceLocation EllipsisLoc,
                                    const ParsedAttributesView &AttrList,
                                    bool IsInstantiation, bool IsUsingIfExists);
   NamedDecl *BuildUsingEnumDeclaration(Scope *S, AccessSpecifier AS,
                                        SourceLocation UsingLoc,
                                        SourceLocation EnumLoc,
                                        SourceLocation NameLoc,
                                        TypeSourceInfo *EnumType, EnumDecl *ED);
   NamedDecl *BuildUsingPackDecl(NamedDecl *InstantiatedFrom,
                                 ArrayRef<NamedDecl *> Expansions);
 
   /// Additional checks for a using declaration referring to a constructor name.
   bool CheckInheritingConstructorUsingDecl(UsingDecl *UD);
 
   /// Given a derived-class using shadow declaration for a constructor and the
   /// correspnding base class constructor, find or create the implicit
   /// synthesized derived class constructor to use for this initialization.
   CXXConstructorDecl *
   findInheritingConstructor(SourceLocation Loc, CXXConstructorDecl *BaseCtor,
                             ConstructorUsingShadowDecl *DerivedShadow);
 
   Decl *ActOnUsingDeclaration(Scope *CurScope, AccessSpecifier AS,
                               SourceLocation UsingLoc,
                               SourceLocation TypenameLoc, CXXScopeSpec &SS,
                               UnqualifiedId &Name, SourceLocation EllipsisLoc,
                               const ParsedAttributesView &AttrList);
   Decl *ActOnUsingEnumDeclaration(Scope *CurScope, AccessSpecifier AS,
                                   SourceLocation UsingLoc,
                                   SourceLocation EnumLoc, SourceRange TyLoc,
                                   const IdentifierInfo &II, ParsedType Ty,
                                   CXXScopeSpec *SS = nullptr);
   Decl *ActOnAliasDeclaration(Scope *CurScope, AccessSpecifier AS,
                               MultiTemplateParamsArg TemplateParams,
                               SourceLocation UsingLoc, UnqualifiedId &Name,
                               const ParsedAttributesView &AttrList,
                               TypeResult Type, Decl *DeclFromDeclSpec);
 
   /// BuildCXXConstructExpr - Creates a complete call to a constructor,
   /// including handling of its default argument expressions.
   ///
   /// \param ConstructKind - a CXXConstructExpr::ConstructionKind
   ExprResult BuildCXXConstructExpr(
       SourceLocation ConstructLoc, QualType DeclInitType, NamedDecl *FoundDecl,
       CXXConstructorDecl *Constructor, MultiExprArg Exprs,
       bool HadMultipleCandidates, bool IsListInitialization,
       bool IsStdInitListInitialization, bool RequiresZeroInit,
       CXXConstructionKind ConstructKind, SourceRange ParenRange);
 
   /// Build a CXXConstructExpr whose constructor has already been resolved if
   /// it denotes an inherited constructor.
   ExprResult BuildCXXConstructExpr(
       SourceLocation ConstructLoc, QualType DeclInitType,
       CXXConstructorDecl *Constructor, bool Elidable, MultiExprArg Exprs,
       bool HadMultipleCandidates, bool IsListInitialization,
       bool IsStdInitListInitialization, bool RequiresZeroInit,
       CXXConstructionKind ConstructKind, SourceRange ParenRange);
 
   // FIXME: Can we remove this and have the above BuildCXXConstructExpr check if
   // the constructor can be elidable?
   ExprResult BuildCXXConstructExpr(
       SourceLocation ConstructLoc, QualType DeclInitType, NamedDecl *FoundDecl,
       CXXConstructorDecl *Constructor, bool Elidable, MultiExprArg Exprs,
       bool HadMultipleCandidates, bool IsListInitialization,
       bool IsStdInitListInitialization, bool RequiresZeroInit,
       CXXConstructionKind ConstructKind, SourceRange ParenRange);
 
   ExprResult ConvertMemberDefaultInitExpression(FieldDecl *FD, Expr *InitExpr,
                                                 SourceLocation InitLoc);
 
   /// FinalizeVarWithDestructor - Prepare for calling destructor on the
   /// constructed variable.
   void FinalizeVarWithDestructor(VarDecl *VD, const RecordType *DeclInitType);
 
   /// Helper class that collects exception specifications for
   /// implicitly-declared special member functions.
   class ImplicitExceptionSpecification {
     // Pointer to allow copying
     Sema *Self;
     // We order exception specifications thus:
     // noexcept is the most restrictive, but is only used in C++11.
     // throw() comes next.
     // Then a throw(collected exceptions)
     // Finally no specification, which is expressed as noexcept(false).
     // throw(...) is used instead if any called function uses it.
     ExceptionSpecificationType ComputedEST;
     llvm::SmallPtrSet<CanQualType, 4> ExceptionsSeen;
     SmallVector<QualType, 4> Exceptions;
 
     void ClearExceptions() {
       ExceptionsSeen.clear();
       Exceptions.clear();
     }
 
   public:
     explicit ImplicitExceptionSpecification(Sema &Self)
         : Self(&Self), ComputedEST(EST_BasicNoexcept) {
       if (!Self.getLangOpts().CPlusPlus11)
         ComputedEST = EST_DynamicNone;
     }
 
     /// Get the computed exception specification type.
     ExceptionSpecificationType getExceptionSpecType() const {
       assert(!isComputedNoexcept(ComputedEST) &&
              "noexcept(expr) should not be a possible result");
       return ComputedEST;
     }
 
     /// The number of exceptions in the exception specification.
     unsigned size() const { return Exceptions.size(); }
 
     /// The set of exceptions in the exception specification.
     const QualType *data() const { return Exceptions.data(); }
 
     /// Integrate another called method into the collected data.
     void CalledDecl(SourceLocation CallLoc, const CXXMethodDecl *Method);
 
     /// Integrate an invoked expression into the collected data.
     void CalledExpr(Expr *E) { CalledStmt(E); }
 
     /// Integrate an invoked statement into the collected data.
     void CalledStmt(Stmt *S);
 
     /// Overwrite an EPI's exception specification with this
     /// computed exception specification.
     FunctionProtoType::ExceptionSpecInfo getExceptionSpec() const {
       FunctionProtoType::ExceptionSpecInfo ESI;
       ESI.Type = getExceptionSpecType();
       if (ESI.Type == EST_Dynamic) {
         ESI.Exceptions = Exceptions;
       } else if (ESI.Type == EST_None) {
         /// C++11 [except.spec]p14:
         ///   The exception-specification is noexcept(false) if the set of
         ///   potential exceptions of the special member function contains "any"
         ESI.Type = EST_NoexceptFalse;
         ESI.NoexceptExpr =
             Self->ActOnCXXBoolLiteral(SourceLocation(), tok::kw_false).get();
       }
       return ESI;
     }
   };
 
   /// Evaluate the implicit exception specification for a defaulted
   /// special member function.
   void EvaluateImplicitExceptionSpec(SourceLocation Loc, FunctionDecl *FD);
 
   /// Check the given exception-specification and update the
   /// exception specification information with the results.
   void checkExceptionSpecification(bool IsTopLevel,
                                    ExceptionSpecificationType EST,
                                    ArrayRef<ParsedType> DynamicExceptions,
                                    ArrayRef<SourceRange> DynamicExceptionRanges,
                                    Expr *NoexceptExpr,
                                    SmallVectorImpl<QualType> &Exceptions,
                                    FunctionProtoType::ExceptionSpecInfo &ESI);
 
   /// Add an exception-specification to the given member or friend function
   /// (or function template). The exception-specification was parsed
   /// after the function itself was declared.
   void actOnDelayedExceptionSpecification(
       Decl *D, ExceptionSpecificationType EST, SourceRange SpecificationRange,
       ArrayRef<ParsedType> DynamicExceptions,
       ArrayRef<SourceRange> DynamicExceptionRanges, Expr *NoexceptExpr);
 
   class InheritedConstructorInfo;
 
   /// Determine if a special member function should have a deleted
   /// definition when it is defaulted.
   bool ShouldDeleteSpecialMember(CXXMethodDecl *MD, CXXSpecialMemberKind CSM,
                                  InheritedConstructorInfo *ICI = nullptr,
                                  bool Diagnose = false);
 
   /// Produce notes explaining why a defaulted function was defined as deleted.
   void DiagnoseDeletedDefaultedFunction(FunctionDecl *FD);
 
   /// Declare the implicit default constructor for the given class.
   ///
   /// \param ClassDecl The class declaration into which the implicit
   /// default constructor will be added.
   ///
   /// \returns The implicitly-declared default constructor.
   CXXConstructorDecl *
   DeclareImplicitDefaultConstructor(CXXRecordDecl *ClassDecl);
 
   /// DefineImplicitDefaultConstructor - Checks for feasibility of
   /// defining this constructor as the default constructor.
   void DefineImplicitDefaultConstructor(SourceLocation CurrentLocation,
                                         CXXConstructorDecl *Constructor);
 
   /// Declare the implicit destructor for the given class.
   ///
   /// \param ClassDecl The class declaration into which the implicit
   /// destructor will be added.
   ///
   /// \returns The implicitly-declared destructor.
   CXXDestructorDecl *DeclareImplicitDestructor(CXXRecordDecl *ClassDecl);
 
   /// DefineImplicitDestructor - Checks for feasibility of
   /// defining this destructor as the default destructor.
   void DefineImplicitDestructor(SourceLocation CurrentLocation,
                                 CXXDestructorDecl *Destructor);
 
   /// Build an exception spec for destructors that don't have one.
   ///
   /// C++11 says that user-defined destructors with no exception spec get one
   /// that looks as if the destructor was implicitly declared.
   void AdjustDestructorExceptionSpec(CXXDestructorDecl *Destructor);
 
   /// Define the specified inheriting constructor.
   void DefineInheritingConstructor(SourceLocation UseLoc,
                                    CXXConstructorDecl *Constructor);
 
   /// Declare the implicit copy constructor for the given class.
   ///
   /// \param ClassDecl The class declaration into which the implicit
   /// copy constructor will be added.
   ///
   /// \returns The implicitly-declared copy constructor.
   CXXConstructorDecl *DeclareImplicitCopyConstructor(CXXRecordDecl *ClassDecl);
 
   /// DefineImplicitCopyConstructor - Checks for feasibility of
   /// defining this constructor as the copy constructor.
   void DefineImplicitCopyConstructor(SourceLocation CurrentLocation,
                                      CXXConstructorDecl *Constructor);
 
   /// Declare the implicit move constructor for the given class.
   ///
   /// \param ClassDecl The Class declaration into which the implicit
   /// move constructor will be added.
   ///
   /// \returns The implicitly-declared move constructor, or NULL if it wasn't
   /// declared.
   CXXConstructorDecl *DeclareImplicitMoveConstructor(CXXRecordDecl *ClassDecl);
 
   /// DefineImplicitMoveConstructor - Checks for feasibility of
   /// defining this constructor as the move constructor.
   void DefineImplicitMoveConstructor(SourceLocation CurrentLocation,
                                      CXXConstructorDecl *Constructor);
 
   /// Declare the implicit copy assignment operator for the given class.
   ///
   /// \param ClassDecl The class declaration into which the implicit
   /// copy assignment operator will be added.
   ///
   /// \returns The implicitly-declared copy assignment operator.
   CXXMethodDecl *DeclareImplicitCopyAssignment(CXXRecordDecl *ClassDecl);
 
   /// Defines an implicitly-declared copy assignment operator.
   void DefineImplicitCopyAssignment(SourceLocation CurrentLocation,
                                     CXXMethodDecl *MethodDecl);
 
   /// Declare the implicit move assignment operator for the given class.
   ///
   /// \param ClassDecl The Class declaration into which the implicit
   /// move assignment operator will be added.
   ///
   /// \returns The implicitly-declared move assignment operator, or NULL if it
   /// wasn't declared.
   CXXMethodDecl *DeclareImplicitMoveAssignment(CXXRecordDecl *ClassDecl);
 
   /// Defines an implicitly-declared move assignment operator.
   void DefineImplicitMoveAssignment(SourceLocation CurrentLocation,
                                     CXXMethodDecl *MethodDecl);
 
   /// Check a completed declaration of an implicit special member.
   void CheckImplicitSpecialMemberDeclaration(Scope *S, FunctionDecl *FD);
 
   /// Determine whether the given function is an implicitly-deleted
   /// special member function.
   bool isImplicitlyDeleted(FunctionDecl *FD);
 
   /// Check whether 'this' shows up in the type of a static member
   /// function after the (naturally empty) cv-qualifier-seq would be.
   ///
   /// \returns true if an error occurred.
   bool checkThisInStaticMemberFunctionType(CXXMethodDecl *Method);
 
   /// Whether this' shows up in the exception specification of a static
   /// member function.
   bool checkThisInStaticMemberFunctionExceptionSpec(CXXMethodDecl *Method);
 
   /// Check whether 'this' shows up in the attributes of the given
   /// static member function.
   ///
   /// \returns true if an error occurred.
   bool checkThisInStaticMemberFunctionAttributes(CXXMethodDecl *Method);
 
   bool CheckImmediateEscalatingFunctionDefinition(
       FunctionDecl *FD, const sema::FunctionScopeInfo *FSI);
 
   void DiagnoseImmediateEscalatingReason(FunctionDecl *FD);
 
   /// Given a constructor and the set of arguments provided for the
   /// constructor, convert the arguments and add any required default arguments
   /// to form a proper call to this constructor.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CompleteConstructorCall(CXXConstructorDecl *Constructor,
                                QualType DeclInitType, MultiExprArg ArgsPtr,
                                SourceLocation Loc,
                                SmallVectorImpl<Expr *> &ConvertedArgs,
                                bool AllowExplicit = false,
                                bool IsListInitialization = false);
 
   /// ActOnCXXEnterDeclInitializer - Invoked when we are about to parse an
   /// initializer for the declaration 'Dcl'.
   /// After this method is called, according to [C++ 3.4.1p13], if 'Dcl' is a
   /// static data member of class X, names should be looked up in the scope of
   /// class X.
   void ActOnCXXEnterDeclInitializer(Scope *S, Decl *Dcl);
 
   /// ActOnCXXExitDeclInitializer - Invoked after we are finished parsing an
   /// initializer for the declaration 'Dcl'.
   void ActOnCXXExitDeclInitializer(Scope *S, Decl *Dcl);
 
   /// Define the "body" of the conversion from a lambda object to a
   /// function pointer.
   ///
   /// This routine doesn't actually define a sensible body; rather, it fills
   /// in the initialization expression needed to copy the lambda object into
   /// the block, and IR generation actually generates the real body of the
   /// block pointer conversion.
   void
   DefineImplicitLambdaToFunctionPointerConversion(SourceLocation CurrentLoc,
                                                   CXXConversionDecl *Conv);
 
   /// Define the "body" of the conversion from a lambda object to a
   /// block pointer.
   ///
   /// This routine doesn't actually define a sensible body; rather, it fills
   /// in the initialization expression needed to copy the lambda object into
   /// the block, and IR generation actually generates the real body of the
   /// block pointer conversion.
   void DefineImplicitLambdaToBlockPointerConversion(SourceLocation CurrentLoc,
                                                     CXXConversionDecl *Conv);
 
   /// ActOnStartLinkageSpecification - Parsed the beginning of a C++
   /// linkage specification, including the language and (if present)
   /// the '{'. ExternLoc is the location of the 'extern', Lang is the
   /// language string literal. LBraceLoc, if valid, provides the location of
   /// the '{' brace. Otherwise, this linkage specification does not
   /// have any braces.
   Decl *ActOnStartLinkageSpecification(Scope *S, SourceLocation ExternLoc,
                                        Expr *LangStr, SourceLocation LBraceLoc);
 
   /// ActOnFinishLinkageSpecification - Complete the definition of
   /// the C++ linkage specification LinkageSpec. If RBraceLoc is
   /// valid, it's the position of the closing '}' brace in a linkage
   /// specification that uses braces.
   Decl *ActOnFinishLinkageSpecification(Scope *S, Decl *LinkageSpec,
                                         SourceLocation RBraceLoc);
 
   //===--------------------------------------------------------------------===//
   // C++ Classes
   //
 
   /// Get the class that is directly named by the current context. This is the
   /// class for which an unqualified-id in this scope could name a constructor
   /// or destructor.
   ///
   /// If the scope specifier denotes a class, this will be that class.
   /// If the scope specifier is empty, this will be the class whose
   /// member-specification we are currently within. Otherwise, there
   /// is no such class.
   CXXRecordDecl *getCurrentClass(Scope *S, const CXXScopeSpec *SS);
 
   /// isCurrentClassName - Determine whether the identifier II is the
   /// name of the class type currently being defined. In the case of
   /// nested classes, this will only return true if II is the name of
   /// the innermost class.
   bool isCurrentClassName(const IdentifierInfo &II, Scope *S,
                           const CXXScopeSpec *SS = nullptr);
 
   /// Determine whether the identifier II is a typo for the name of
   /// the class type currently being defined. If so, update it to the identifier
   /// that should have been used.
   bool isCurrentClassNameTypo(IdentifierInfo *&II, const CXXScopeSpec *SS);
 
   /// ActOnAccessSpecifier - Parsed an access specifier followed by a colon.
   bool ActOnAccessSpecifier(AccessSpecifier Access, SourceLocation ASLoc,
                             SourceLocation ColonLoc,
                             const ParsedAttributesView &Attrs);
 
   /// ActOnCXXMemberDeclarator - This is invoked when a C++ class member
   /// declarator is parsed. 'AS' is the access specifier, 'BW' specifies the
   /// bitfield width if there is one, 'InitExpr' specifies the initializer if
   /// one has been parsed, and 'InitStyle' is set if an in-class initializer is
   /// present (but parsing it has been deferred).
   NamedDecl *
   ActOnCXXMemberDeclarator(Scope *S, AccessSpecifier AS, Declarator &D,
                            MultiTemplateParamsArg TemplateParameterLists,
                            Expr *BitfieldWidth, const VirtSpecifiers &VS,
                            InClassInitStyle InitStyle);
 
   /// Enter a new C++ default initializer scope. After calling this, the
   /// caller must call \ref ActOnFinishCXXInClassMemberInitializer, even if
   /// parsing or instantiating the initializer failed.
   void ActOnStartCXXInClassMemberInitializer();
 
   /// This is invoked after parsing an in-class initializer for a
   /// non-static C++ class member, and after instantiating an in-class
   /// initializer in a class template. Such actions are deferred until the class
   /// is complete.
   void ActOnFinishCXXInClassMemberInitializer(Decl *VarDecl,
                                               SourceLocation EqualLoc,
                                               ExprResult Init);
 
   /// Handle a C++ member initializer using parentheses syntax.
   MemInitResult
   ActOnMemInitializer(Decl *ConstructorD, Scope *S, CXXScopeSpec &SS,
                       IdentifierInfo *MemberOrBase, ParsedType TemplateTypeTy,
                       const DeclSpec &DS, SourceLocation IdLoc,
                       SourceLocation LParenLoc, ArrayRef<Expr *> Args,
                       SourceLocation RParenLoc, SourceLocation EllipsisLoc);
 
   /// Handle a C++ member initializer using braced-init-list syntax.
   MemInitResult ActOnMemInitializer(Decl *ConstructorD, Scope *S,
                                     CXXScopeSpec &SS,
                                     IdentifierInfo *MemberOrBase,
                                     ParsedType TemplateTypeTy,
                                     const DeclSpec &DS, SourceLocation IdLoc,
                                     Expr *InitList, SourceLocation EllipsisLoc);
 
   /// Handle a C++ member initializer.
   MemInitResult BuildMemInitializer(Decl *ConstructorD, Scope *S,
                                     CXXScopeSpec &SS,
                                     IdentifierInfo *MemberOrBase,
                                     ParsedType TemplateTypeTy,
                                     const DeclSpec &DS, SourceLocation IdLoc,
                                     Expr *Init, SourceLocation EllipsisLoc);
 
   MemInitResult BuildMemberInitializer(ValueDecl *Member, Expr *Init,
                                        SourceLocation IdLoc);
 
   MemInitResult BuildBaseInitializer(QualType BaseType,
                                      TypeSourceInfo *BaseTInfo, Expr *Init,
                                      CXXRecordDecl *ClassDecl,
                                      SourceLocation EllipsisLoc);
 
   MemInitResult BuildDelegatingInitializer(TypeSourceInfo *TInfo, Expr *Init,
                                            CXXRecordDecl *ClassDecl);
 
   bool SetDelegatingInitializer(CXXConstructorDecl *Constructor,
                                 CXXCtorInitializer *Initializer);
 
   bool SetCtorInitializers(CXXConstructorDecl *Constructor, bool AnyErrors,
                            ArrayRef<CXXCtorInitializer *> Initializers = {});
 
   /// MarkBaseAndMemberDestructorsReferenced - Given a record decl,
   /// mark all the non-trivial destructors of its members and bases as
   /// referenced.
   void MarkBaseAndMemberDestructorsReferenced(SourceLocation Loc,
                                               CXXRecordDecl *Record);
 
   /// Mark destructors of virtual bases of this class referenced. In the Itanium
   /// C++ ABI, this is done when emitting a destructor for any non-abstract
   /// class. In the Microsoft C++ ABI, this is done any time a class's
   /// destructor is referenced.
   void MarkVirtualBaseDestructorsReferenced(
       SourceLocation Location, CXXRecordDecl *ClassDecl,
       llvm::SmallPtrSetImpl<const RecordType *> *DirectVirtualBases = nullptr);
 
   /// Do semantic checks to allow the complete destructor variant to be emitted
   /// when the destructor is defined in another translation unit. In the Itanium
   /// C++ ABI, destructor variants are emitted together. In the MS C++ ABI, they
   /// can be emitted in separate TUs. To emit the complete variant, run a subset
   /// of the checks performed when emitting a regular destructor.
   void CheckCompleteDestructorVariant(SourceLocation CurrentLocation,
                                       CXXDestructorDecl *Dtor);
 
   /// The list of classes whose vtables have been used within
   /// this translation unit, and the source locations at which the
   /// first use occurred.
   typedef std::pair<CXXRecordDecl *, SourceLocation> VTableUse;
 
   /// The list of vtables that are required but have not yet been
   /// materialized.
   SmallVector<VTableUse, 16> VTableUses;
 
   /// The set of classes whose vtables have been used within
   /// this translation unit, and a bit that will be true if the vtable is
   /// required to be emitted (otherwise, it should be emitted only if needed
   /// by code generation).
   llvm::DenseMap<CXXRecordDecl *, bool> VTablesUsed;
 
   /// Load any externally-stored vtable uses.
   void LoadExternalVTableUses();
 
   /// Note that the vtable for the given class was used at the
   /// given location.
   void MarkVTableUsed(SourceLocation Loc, CXXRecordDecl *Class,
                       bool DefinitionRequired = false);
 
   /// Mark the exception specifications of all virtual member functions
   /// in the given class as needed.
   void MarkVirtualMemberExceptionSpecsNeeded(SourceLocation Loc,
                                              const CXXRecordDecl *RD);
 
   /// MarkVirtualMembersReferenced - Will mark all members of the given
   /// CXXRecordDecl referenced.
   void MarkVirtualMembersReferenced(SourceLocation Loc, const CXXRecordDecl *RD,
                                     bool ConstexprOnly = false);
 
   /// Define all of the vtables that have been used in this
   /// translation unit and reference any virtual members used by those
   /// vtables.
   ///
   /// \returns true if any work was done, false otherwise.
   bool DefineUsedVTables();
 
   /// AddImplicitlyDeclaredMembersToClass - Adds any implicitly-declared
   /// special functions, such as the default constructor, copy
   /// constructor, or destructor, to the given C++ class (C++
   /// [special]p1).  This routine can only be executed just before the
   /// definition of the class is complete.
   void AddImplicitlyDeclaredMembersToClass(CXXRecordDecl *ClassDecl);
 
   /// ActOnMemInitializers - Handle the member initializers for a constructor.
   void ActOnMemInitializers(Decl *ConstructorDecl, SourceLocation ColonLoc,
                             ArrayRef<CXXCtorInitializer *> MemInits,
                             bool AnyErrors);
 
   /// Check class-level dllimport/dllexport attribute. The caller must
   /// ensure that referenceDLLExportedClassMethods is called some point later
   /// when all outer classes of Class are complete.
   void checkClassLevelDLLAttribute(CXXRecordDecl *Class);
   void checkClassLevelCodeSegAttribute(CXXRecordDecl *Class);
 
   void referenceDLLExportedClassMethods();
 
   /// Perform propagation of DLL attributes from a derived class to a
   /// templated base class for MS compatibility.
   void propagateDLLAttrToBaseClassTemplate(
       CXXRecordDecl *Class, Attr *ClassAttr,
       ClassTemplateSpecializationDecl *BaseTemplateSpec,
       SourceLocation BaseLoc);
 
   /// Perform semantic checks on a class definition that has been
   /// completing, introducing implicitly-declared members, checking for
   /// abstract types, etc.
   ///
   /// \param S The scope in which the class was parsed. Null if we didn't just
   ///        parse a class definition.
   /// \param Record The completed class.
   void CheckCompletedCXXClass(Scope *S, CXXRecordDecl *Record);
 
   /// Check that the C++ class annoated with "trivial_abi" satisfies all the
   /// conditions that are needed for the attribute to have an effect.
   void checkIllFormedTrivialABIStruct(CXXRecordDecl &RD);
 
   /// Check that VTable Pointer authentication is only being set on the first
   /// first instantiation of the vtable
   void checkIncorrectVTablePointerAuthenticationAttribute(CXXRecordDecl &RD);
 
   void ActOnFinishCXXMemberSpecification(Scope *S, SourceLocation RLoc,
                                          Decl *TagDecl, SourceLocation LBrac,
                                          SourceLocation RBrac,
                                          const ParsedAttributesView &AttrList);
 
   /// Perform any semantic analysis which needs to be delayed until all
   /// pending class member declarations have been parsed.
   void ActOnFinishCXXMemberDecls();
   void ActOnFinishCXXNonNestedClass();
 
   /// This is used to implement the constant expression evaluation part of the
   /// attribute enable_if extension. There is nothing in standard C++ which
   /// would require reentering parameters.
   void ActOnReenterCXXMethodParameter(Scope *S, ParmVarDecl *Param);
   unsigned ActOnReenterTemplateScope(Decl *Template,
                                      llvm::function_ref<Scope *()> EnterScope);
   void ActOnStartDelayedMemberDeclarations(Scope *S, Decl *Record);
 
   /// ActOnStartDelayedCXXMethodDeclaration - We have completed
   /// parsing a top-level (non-nested) C++ class, and we are now
   /// parsing those parts of the given Method declaration that could
   /// not be parsed earlier (C++ [class.mem]p2), such as default
   /// arguments. This action should enter the scope of the given
   /// Method declaration as if we had just parsed the qualified method
   /// name. However, it should not bring the parameters into scope;
   /// that will be performed by ActOnDelayedCXXMethodParameter.
   void ActOnStartDelayedCXXMethodDeclaration(Scope *S, Decl *Method);
   void ActOnDelayedCXXMethodParameter(Scope *S, Decl *Param);
   void ActOnFinishDelayedMemberDeclarations(Scope *S, Decl *Record);
 
   /// ActOnFinishDelayedCXXMethodDeclaration - We have finished
   /// processing the delayed method declaration for Method. The method
   /// declaration is now considered finished. There may be a separate
   /// ActOnStartOfFunctionDef action later (not necessarily
   /// immediately!) for this method, if it was also defined inside the
   /// class body.
   void ActOnFinishDelayedCXXMethodDeclaration(Scope *S, Decl *Method);
   void ActOnFinishDelayedMemberInitializers(Decl *Record);
 
   bool EvaluateStaticAssertMessageAsString(Expr *Message, std::string &Result,
                                            ASTContext &Ctx,
                                            bool ErrorOnInvalidMessage);
   Decl *ActOnStaticAssertDeclaration(SourceLocation StaticAssertLoc,
                                      Expr *AssertExpr, Expr *AssertMessageExpr,
                                      SourceLocation RParenLoc);
   Decl *BuildStaticAssertDeclaration(SourceLocation StaticAssertLoc,
                                      Expr *AssertExpr, Expr *AssertMessageExpr,
                                      SourceLocation RParenLoc, bool Failed);
 
   /// Try to print more useful information about a failed static_assert
   /// with expression \E
   void DiagnoseStaticAssertDetails(const Expr *E);
 
   /// Handle a friend type declaration.  This works in tandem with
   /// ActOnTag.
   ///
   /// Notes on friend class templates:
   ///
   /// We generally treat friend class declarations as if they were
   /// declaring a class.  So, for example, the elaborated type specifier
   /// in a friend declaration is required to obey the restrictions of a
   /// class-head (i.e. no typedefs in the scope chain), template
   /// parameters are required to match up with simple template-ids, &c.
   /// However, unlike when declaring a template specialization, it's
   /// okay to refer to a template specialization without an empty
   /// template parameter declaration, e.g.
   ///   friend class A<T>::B<unsigned>;
   /// We permit this as a special case; if there are any template
   /// parameters present at all, require proper matching, i.e.
   ///   template <> template \<class T> friend class A<int>::B;
   Decl *ActOnFriendTypeDecl(Scope *S, const DeclSpec &DS,
                             MultiTemplateParamsArg TemplateParams,
                             SourceLocation EllipsisLoc);
   NamedDecl *ActOnFriendFunctionDecl(Scope *S, Declarator &D,
                                      MultiTemplateParamsArg TemplateParams);
 
   /// CheckConstructorDeclarator - Called by ActOnDeclarator to check
   /// the well-formedness of the constructor declarator @p D with type @p
   /// R. If there are any errors in the declarator, this routine will
   /// emit diagnostics and set the invalid bit to true.  In any case, the type
   /// will be updated to reflect a well-formed type for the constructor and
   /// returned.
   QualType CheckConstructorDeclarator(Declarator &D, QualType R,
                                       StorageClass &SC);
 
   /// CheckConstructor - Checks a fully-formed constructor for
   /// well-formedness, issuing any diagnostics required. Returns true if
   /// the constructor declarator is invalid.
   void CheckConstructor(CXXConstructorDecl *Constructor);
 
   /// CheckDestructorDeclarator - Called by ActOnDeclarator to check
   /// the well-formednes of the destructor declarator @p D with type @p
   /// R. If there are any errors in the declarator, this routine will
   /// emit diagnostics and set the declarator to invalid.  Even if this happens,
   /// will be updated to reflect a well-formed type for the destructor and
   /// returned.
   QualType CheckDestructorDeclarator(Declarator &D, QualType R,
                                      StorageClass &SC);
 
   /// CheckDestructor - Checks a fully-formed destructor definition for
   /// well-formedness, issuing any diagnostics required.  Returns true
   /// on error.
   bool CheckDestructor(CXXDestructorDecl *Destructor);
 
   /// CheckConversionDeclarator - Called by ActOnDeclarator to check the
   /// well-formednes of the conversion function declarator @p D with
   /// type @p R. If there are any errors in the declarator, this routine
   /// will emit diagnostics and return true. Otherwise, it will return
   /// false. Either way, the type @p R will be updated to reflect a
   /// well-formed type for the conversion operator.
   void CheckConversionDeclarator(Declarator &D, QualType &R, StorageClass &SC);
 
   /// ActOnConversionDeclarator - Called by ActOnDeclarator to complete
   /// the declaration of the given C++ conversion function. This routine
   /// is responsible for recording the conversion function in the C++
   /// class, if possible.
   Decl *ActOnConversionDeclarator(CXXConversionDecl *Conversion);
 
   /// Check the validity of a declarator that we parsed for a deduction-guide.
   /// These aren't actually declarators in the grammar, so we need to check that
   /// the user didn't specify any pieces that are not part of the
   /// deduction-guide grammar. Return true on invalid deduction-guide.
   bool CheckDeductionGuideDeclarator(Declarator &D, QualType &R,
                                      StorageClass &SC);
 
   void CheckExplicitlyDefaultedFunction(Scope *S, FunctionDecl *MD);
 
   bool CheckExplicitlyDefaultedSpecialMember(CXXMethodDecl *MD,
                                              CXXSpecialMemberKind CSM,
                                              SourceLocation DefaultLoc);
   void CheckDelayedMemberExceptionSpecs();
 
   /// Kinds of defaulted comparison operator functions.
   enum class DefaultedComparisonKind : unsigned char {
     /// This is not a defaultable comparison operator.
     None,
     /// This is an operator== that should be implemented as a series of
     /// subobject comparisons.
     Equal,
     /// This is an operator<=> that should be implemented as a series of
     /// subobject comparisons.
     ThreeWay,
     /// This is an operator!= that should be implemented as a rewrite in terms
     /// of a == comparison.
     NotEqual,
     /// This is an <, <=, >, or >= that should be implemented as a rewrite in
     /// terms of a <=> comparison.
     Relational,
   };
 
   bool CheckExplicitlyDefaultedComparison(Scope *S, FunctionDecl *MD,
                                           DefaultedComparisonKind DCK);
   void DeclareImplicitEqualityComparison(CXXRecordDecl *RD,
                                          FunctionDecl *Spaceship);
   void DefineDefaultedComparison(SourceLocation Loc, FunctionDecl *FD,
                                  DefaultedComparisonKind DCK);
 
   void CheckExplicitObjectMemberFunction(Declarator &D, DeclarationName Name,
                                          QualType R, bool IsLambda,
                                          DeclContext *DC = nullptr);
   void CheckExplicitObjectMemberFunction(DeclContext *DC, Declarator &D,
                                          DeclarationName Name, QualType R);
   void CheckExplicitObjectLambda(Declarator &D);
 
   //===--------------------------------------------------------------------===//
   // C++ Derived Classes
   //
 
   /// Check the validity of a C++ base class specifier.
   ///
   /// \returns a new CXXBaseSpecifier if well-formed, emits diagnostics
   /// and returns NULL otherwise.
   CXXBaseSpecifier *CheckBaseSpecifier(CXXRecordDecl *Class,
                                        SourceRange SpecifierRange, bool Virtual,
                                        AccessSpecifier Access,
                                        TypeSourceInfo *TInfo,
                                        SourceLocation EllipsisLoc);
 
   /// ActOnBaseSpecifier - Parsed a base specifier. A base specifier is
   /// one entry in the base class list of a class specifier, for
   /// example:
   ///    class foo : public bar, virtual private baz {
   /// 'public bar' and 'virtual private baz' are each base-specifiers.
   BaseResult ActOnBaseSpecifier(Decl *classdecl, SourceRange SpecifierRange,
                                 const ParsedAttributesView &Attrs, bool Virtual,
                                 AccessSpecifier Access, ParsedType basetype,
                                 SourceLocation BaseLoc,
                                 SourceLocation EllipsisLoc);
 
   /// Performs the actual work of attaching the given base class
   /// specifiers to a C++ class.
   bool AttachBaseSpecifiers(CXXRecordDecl *Class,
                             MutableArrayRef<CXXBaseSpecifier *> Bases);
 
   /// ActOnBaseSpecifiers - Attach the given base specifiers to the
   /// class, after checking whether there are any duplicate base
   /// classes.
   void ActOnBaseSpecifiers(Decl *ClassDecl,
                            MutableArrayRef<CXXBaseSpecifier *> Bases);
 
   /// Determine whether the type \p Derived is a C++ class that is
   /// derived from the type \p Base.
   bool IsDerivedFrom(SourceLocation Loc, QualType Derived, QualType Base);
 
   /// Determine whether the type \p Derived is a C++ class that is
   /// derived from the type \p Base.
   bool IsDerivedFrom(SourceLocation Loc, QualType Derived, QualType Base,
                      CXXBasePaths &Paths);
 
   // FIXME: I don't like this name.
   void BuildBasePathArray(const CXXBasePaths &Paths, CXXCastPath &BasePath);
 
   bool CheckDerivedToBaseConversion(QualType Derived, QualType Base,
                                     SourceLocation Loc, SourceRange Range,
                                     CXXCastPath *BasePath = nullptr,
                                     bool IgnoreAccess = false);
 
   /// CheckDerivedToBaseConversion - Check whether the Derived-to-Base
   /// conversion (where Derived and Base are class types) is
   /// well-formed, meaning that the conversion is unambiguous (and
   /// that all of the base classes are accessible). Returns true
   /// and emits a diagnostic if the code is ill-formed, returns false
   /// otherwise. Loc is the location where this routine should point to
   /// if there is an error, and Range is the source range to highlight
   /// if there is an error.
   ///
   /// If either InaccessibleBaseID or AmbiguousBaseConvID are 0, then the
   /// diagnostic for the respective type of error will be suppressed, but the
   /// check for ill-formed code will still be performed.
   bool CheckDerivedToBaseConversion(QualType Derived, QualType Base,
                                     unsigned InaccessibleBaseID,
                                     unsigned AmbiguousBaseConvID,
                                     SourceLocation Loc, SourceRange Range,
                                     DeclarationName Name, CXXCastPath *BasePath,
                                     bool IgnoreAccess = false);
 
   /// Builds a string representing ambiguous paths from a
   /// specific derived class to different subobjects of the same base
   /// class.
   ///
   /// This function builds a string that can be used in error messages
   /// to show the different paths that one can take through the
   /// inheritance hierarchy to go from the derived class to different
   /// subobjects of a base class. The result looks something like this:
   /// @code
   /// struct D -> struct B -> struct A
   /// struct D -> struct C -> struct A
   /// @endcode
   std::string getAmbiguousPathsDisplayString(CXXBasePaths &Paths);
 
   bool CheckOverridingFunctionAttributes(CXXMethodDecl *New,
                                          const CXXMethodDecl *Old);
 
   /// CheckOverridingFunctionReturnType - Checks whether the return types are
   /// covariant, according to C++ [class.virtual]p5.
   bool CheckOverridingFunctionReturnType(const CXXMethodDecl *New,
                                          const CXXMethodDecl *Old);
 
   // Check that the overriding method has no explicit object parameter.
   bool CheckExplicitObjectOverride(CXXMethodDecl *New,
                                    const CXXMethodDecl *Old);
 
   /// Mark the given method pure.
   ///
   /// \param Method the method to be marked pure.
   ///
   /// \param InitRange the source range that covers the "0" initializer.
   bool CheckPureMethod(CXXMethodDecl *Method, SourceRange InitRange);
 
   /// CheckOverrideControl - Check C++11 override control semantics.
   void CheckOverrideControl(NamedDecl *D);
 
   /// DiagnoseAbsenceOfOverrideControl - Diagnose if 'override' keyword was
   /// not used in the declaration of an overriding method.
   void DiagnoseAbsenceOfOverrideControl(NamedDecl *D, bool Inconsistent);
 
   /// CheckIfOverriddenFunctionIsMarkedFinal - Checks whether a virtual member
   /// function overrides a virtual member function marked 'final', according to
   /// C++11 [class.virtual]p4.
   bool CheckIfOverriddenFunctionIsMarkedFinal(const CXXMethodDecl *New,
                                               const CXXMethodDecl *Old);
 
   enum AbstractDiagSelID {
     AbstractNone = -1,
     AbstractReturnType,
     AbstractParamType,
     AbstractVariableType,
     AbstractFieldType,
     AbstractIvarType,
     AbstractSynthesizedIvarType,
     AbstractArrayType
   };
 
   struct TypeDiagnoser;
 
   bool isAbstractType(SourceLocation Loc, QualType T);
   bool RequireNonAbstractType(SourceLocation Loc, QualType T,
                               TypeDiagnoser &Diagnoser);
   template <typename... Ts>
   bool RequireNonAbstractType(SourceLocation Loc, QualType T, unsigned DiagID,
                               const Ts &...Args) {
     BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireNonAbstractType(Loc, T, Diagnoser);
   }
 
   void DiagnoseAbstractType(const CXXRecordDecl *RD);
 
   //===--------------------------------------------------------------------===//
   // C++ Overloaded Operators [C++ 13.5]
   //
 
   /// CheckOverloadedOperatorDeclaration - Check whether the declaration
   /// of this overloaded operator is well-formed. If so, returns false;
   /// otherwise, emits appropriate diagnostics and returns true.
   bool CheckOverloadedOperatorDeclaration(FunctionDecl *FnDecl);
 
   /// CheckLiteralOperatorDeclaration - Check whether the declaration
   /// of this literal operator function is well-formed. If so, returns
   /// false; otherwise, emits appropriate diagnostics and returns true.
   bool CheckLiteralOperatorDeclaration(FunctionDecl *FnDecl);
 
   /// ActOnExplicitBoolSpecifier - Build an ExplicitSpecifier from an expression
   /// found in an explicit(bool) specifier.
   ExplicitSpecifier ActOnExplicitBoolSpecifier(Expr *E);
 
   /// tryResolveExplicitSpecifier - Attempt to resolve the explict specifier.
   /// Returns true if the explicit specifier is now resolved.
   bool tryResolveExplicitSpecifier(ExplicitSpecifier &ExplicitSpec);
 
   /// ActOnCXXConditionDeclarationExpr - Parsed a condition declaration of a
   /// C++ if/switch/while/for statement.
   /// e.g: "if (int x = f()) {...}"
   DeclResult ActOnCXXConditionDeclaration(Scope *S, Declarator &D);
 
   // Emitting members of dllexported classes is delayed until the class
   // (including field initializers) is fully parsed.
   SmallVector<CXXRecordDecl *, 4> DelayedDllExportClasses;
   SmallVector<CXXMethodDecl *, 4> DelayedDllExportMemberFunctions;
 
   /// Merge the exception specifications of two variable declarations.
   ///
   /// This is called when there's a redeclaration of a VarDecl. The function
   /// checks if the redeclaration might have an exception specification and
   /// validates compatibility and merges the specs if necessary.
   void MergeVarDeclExceptionSpecs(VarDecl *New, VarDecl *Old);
 
   /// MergeCXXFunctionDecl - Merge two declarations of the same C++
   /// function, once we already know that they have the same
   /// type. Subroutine of MergeFunctionDecl. Returns true if there was an
   /// error, false otherwise.
   bool MergeCXXFunctionDecl(FunctionDecl *New, FunctionDecl *Old, Scope *S);
 
   /// Helpers for dealing with blocks and functions.
   void CheckCXXDefaultArguments(FunctionDecl *FD);
 
   /// CheckExtraCXXDefaultArguments - Check for any extra default
   /// arguments in the declarator, which is not a function declaration
   /// or definition and therefore is not permitted to have default
   /// arguments. This routine should be invoked for every declarator
   /// that is not a function declaration or definition.
   void CheckExtraCXXDefaultArguments(Declarator &D);
 
   CXXSpecialMemberKind getSpecialMember(const CXXMethodDecl *MD) {
     return getDefaultedFunctionKind(MD).asSpecialMember();
   }
 
   /// Perform semantic analysis for the variable declaration that
   /// occurs within a C++ catch clause, returning the newly-created
   /// variable.
   VarDecl *BuildExceptionDeclaration(Scope *S, TypeSourceInfo *TInfo,
                                      SourceLocation StartLoc,
                                      SourceLocation IdLoc,
                                      const IdentifierInfo *Id);
 
   /// ActOnExceptionDeclarator - Parsed the exception-declarator in a C++ catch
   /// handler.
   Decl *ActOnExceptionDeclarator(Scope *S, Declarator &D);
 
   void DiagnoseReturnInConstructorExceptionHandler(CXXTryStmt *TryBlock);
 
   /// Handle a friend tag declaration where the scope specifier was
   /// templated.
   DeclResult ActOnTemplatedFriendTag(Scope *S, SourceLocation FriendLoc,
                                      unsigned TagSpec, SourceLocation TagLoc,
                                      CXXScopeSpec &SS, IdentifierInfo *Name,
                                      SourceLocation NameLoc,
                                      SourceLocation EllipsisLoc,
                                      const ParsedAttributesView &Attr,
                                      MultiTemplateParamsArg TempParamLists);
 
   MSPropertyDecl *HandleMSProperty(Scope *S, RecordDecl *TagD,
                                    SourceLocation DeclStart, Declarator &D,
                                    Expr *BitfieldWidth,
                                    InClassInitStyle InitStyle,
                                    AccessSpecifier AS,
                                    const ParsedAttr &MSPropertyAttr);
 
   /// Diagnose why the specified class does not have a trivial special member of
   /// the given kind.
   void DiagnoseNontrivial(const CXXRecordDecl *Record,
                           CXXSpecialMemberKind CSM);
 
   enum TrivialABIHandling {
     /// The triviality of a method unaffected by "trivial_abi".
     TAH_IgnoreTrivialABI,
 
     /// The triviality of a method affected by "trivial_abi".
     TAH_ConsiderTrivialABI
   };
 
   /// Determine whether a defaulted or deleted special member function is
   /// trivial, as specified in C++11 [class.ctor]p5, C++11 [class.copy]p12,
   /// C++11 [class.copy]p25, and C++11 [class.dtor]p5.
   bool SpecialMemberIsTrivial(CXXMethodDecl *MD, CXXSpecialMemberKind CSM,
                               TrivialABIHandling TAH = TAH_IgnoreTrivialABI,
                               bool Diagnose = false);
 
   /// For a defaulted function, the kind of defaulted function that it is.
   class DefaultedFunctionKind {
     LLVM_PREFERRED_TYPE(CXXSpecialMemberKind)
     unsigned SpecialMember : 8;
     unsigned Comparison : 8;
 
   public:
     DefaultedFunctionKind()
         : SpecialMember(llvm::to_underlying(CXXSpecialMemberKind::Invalid)),
           Comparison(llvm::to_underlying(DefaultedComparisonKind::None)) {}
     DefaultedFunctionKind(CXXSpecialMemberKind CSM)
         : SpecialMember(llvm::to_underlying(CSM)),
           Comparison(llvm::to_underlying(DefaultedComparisonKind::None)) {}
     DefaultedFunctionKind(DefaultedComparisonKind Comp)
         : SpecialMember(llvm::to_underlying(CXXSpecialMemberKind::Invalid)),
           Comparison(llvm::to_underlying(Comp)) {}
 
     bool isSpecialMember() const {
       return static_cast<CXXSpecialMemberKind>(SpecialMember) !=
              CXXSpecialMemberKind::Invalid;
     }
     bool isComparison() const {
       return static_cast<DefaultedComparisonKind>(Comparison) !=
              DefaultedComparisonKind::None;
     }
 
     explicit operator bool() const {
       return isSpecialMember() || isComparison();
     }
 
     CXXSpecialMemberKind asSpecialMember() const {
       return static_cast<CXXSpecialMemberKind>(SpecialMember);
     }
     DefaultedComparisonKind asComparison() const {
       return static_cast<DefaultedComparisonKind>(Comparison);
     }
 
     /// Get the index of this function kind for use in diagnostics.
     unsigned getDiagnosticIndex() const {
       static_assert(llvm::to_underlying(CXXSpecialMemberKind::Invalid) >
                         llvm::to_underlying(CXXSpecialMemberKind::Destructor),
                     "invalid should have highest index");
       static_assert((unsigned)DefaultedComparisonKind::None == 0,
                     "none should be equal to zero");
       return SpecialMember + Comparison;
     }
   };
 
   /// Determine the kind of defaulting that would be done for a given function.
   ///
   /// If the function is both a default constructor and a copy / move
   /// constructor (due to having a default argument for the first parameter),
   /// this picks CXXSpecialMemberKind::DefaultConstructor.
   ///
   /// FIXME: Check that case is properly handled by all callers.
   DefaultedFunctionKind getDefaultedFunctionKind(const FunctionDecl *FD);
 
   /// Handle a C++11 empty-declaration and attribute-declaration.
   Decl *ActOnEmptyDeclaration(Scope *S, const ParsedAttributesView &AttrList,
                               SourceLocation SemiLoc);
 
   enum class CheckConstexprKind {
     /// Diagnose issues that are non-constant or that are extensions.
     Diagnose,
     /// Identify whether this function satisfies the formal rules for constexpr
     /// functions in the current lanugage mode (with no extensions).
     CheckValid
   };
 
   // Check whether a function declaration satisfies the requirements of a
   // constexpr function definition or a constexpr constructor definition. If so,
   // return true. If not, produce appropriate diagnostics (unless asked not to
   // by Kind) and return false.
   //
   // This implements C++11 [dcl.constexpr]p3,4, as amended by DR1360.
   bool CheckConstexprFunctionDefinition(const FunctionDecl *FD,
                                         CheckConstexprKind Kind);
 
   /// Diagnose methods which overload virtual methods in a base class
   /// without overriding any.
   void DiagnoseHiddenVirtualMethods(CXXMethodDecl *MD);
 
   /// Check if a method overloads virtual methods in a base class without
   /// overriding any.
   void
   FindHiddenVirtualMethods(CXXMethodDecl *MD,
                            SmallVectorImpl<CXXMethodDecl *> &OverloadedMethods);
   void
   NoteHiddenVirtualMethods(CXXMethodDecl *MD,
                            SmallVectorImpl<CXXMethodDecl *> &OverloadedMethods);
 
   /// ActOnParamDefaultArgument - Check whether the default argument
   /// provided for a function parameter is well-formed. If so, attach it
   /// to the parameter declaration.
   void ActOnParamDefaultArgument(Decl *param, SourceLocation EqualLoc,
                                  Expr *defarg);
 
   /// ActOnParamUnparsedDefaultArgument - We've seen a default
   /// argument for a function parameter, but we can't parse it yet
   /// because we're inside a class definition. Note that this default
   /// argument will be parsed later.
   void ActOnParamUnparsedDefaultArgument(Decl *param, SourceLocation EqualLoc,
                                          SourceLocation ArgLoc);
 
   /// ActOnParamDefaultArgumentError - Parsing or semantic analysis of
   /// the default argument for the parameter param failed.
   void ActOnParamDefaultArgumentError(Decl *param, SourceLocation EqualLoc,
                                       Expr *DefaultArg);
   ExprResult ConvertParamDefaultArgument(ParmVarDecl *Param, Expr *DefaultArg,
                                          SourceLocation EqualLoc);
   void SetParamDefaultArgument(ParmVarDecl *Param, Expr *DefaultArg,
                                SourceLocation EqualLoc);
 
   void ActOnPureSpecifier(Decl *D, SourceLocation PureSpecLoc);
   void SetDeclDeleted(Decl *dcl, SourceLocation DelLoc,
                       StringLiteral *Message = nullptr);
   void SetDeclDefaulted(Decl *dcl, SourceLocation DefaultLoc);
 
   void SetFunctionBodyKind(Decl *D, SourceLocation Loc, FnBodyKind BodyKind,
                            StringLiteral *DeletedMessage = nullptr);
   void ActOnStartTrailingRequiresClause(Scope *S, Declarator &D);
   ExprResult ActOnFinishTrailingRequiresClause(ExprResult ConstraintExpr);
   ExprResult ActOnRequiresClause(ExprResult ConstraintExpr);
 
   NamedDecl *
   ActOnDecompositionDeclarator(Scope *S, Declarator &D,
                                MultiTemplateParamsArg TemplateParamLists);
   void DiagPlaceholderVariableDefinition(SourceLocation Loc);
   bool DiagRedefinedPlaceholderFieldDecl(SourceLocation Loc,
                                          RecordDecl *ClassDecl,
                                          const IdentifierInfo *Name);
 
   void CheckCompleteDecompositionDeclaration(DecompositionDecl *DD);
 
   /// Stack containing information needed when in C++2a an 'auto' is encountered
   /// in a function declaration parameter type specifier in order to invent a
   /// corresponding template parameter in the enclosing abbreviated function
   /// template. This information is also present in LambdaScopeInfo, stored in
   /// the FunctionScopes stack.
   SmallVector<InventedTemplateParameterInfo, 4> InventedParameterInfos;
 
   /// FieldCollector - Collects CXXFieldDecls during parsing of C++ classes.
   std::unique_ptr<CXXFieldCollector> FieldCollector;
 
   typedef llvm::SmallSetVector<const NamedDecl *, 16> NamedDeclSetType;
   /// Set containing all declared private fields that are not used.
   NamedDeclSetType UnusedPrivateFields;
 
   typedef llvm::SmallPtrSet<const CXXRecordDecl *, 8> RecordDeclSetTy;
 
   /// PureVirtualClassDiagSet - a set of class declarations which we have
   /// emitted a list of pure virtual functions. Used to prevent emitting the
   /// same list more than once.
   std::unique_ptr<RecordDeclSetTy> PureVirtualClassDiagSet;
 
   typedef LazyVector<CXXConstructorDecl *, ExternalSemaSource,
                      &ExternalSemaSource::ReadDelegatingConstructors, 2, 2>
       DelegatingCtorDeclsType;
 
   /// All the delegating constructors seen so far in the file, used for
   /// cycle detection at the end of the TU.
   DelegatingCtorDeclsType DelegatingCtorDecls;
 
   /// The C++ "std" namespace, where the standard library resides.
   LazyDeclPtr StdNamespace;
 
   /// The C++ "std::initializer_list" template, which is defined in
   /// \<initializer_list>.
   ClassTemplateDecl *StdInitializerList;
 
   // Contains the locations of the beginning of unparsed default
   // argument locations.
   llvm::DenseMap<ParmVarDecl *, SourceLocation> UnparsedDefaultArgLocs;
 
   /// UndefinedInternals - all the used, undefined objects which require a
   /// definition in this translation unit.
   llvm::MapVector<NamedDecl *, SourceLocation> UndefinedButUsed;
 
   typedef llvm::PointerIntPair<CXXRecordDecl *, 3, CXXSpecialMemberKind>
       SpecialMemberDecl;
 
   /// The C++ special members which we are currently in the process of
   /// declaring. If this process recursively triggers the declaration of the
   /// same special member, we should act as if it is not yet declared.
   llvm::SmallPtrSet<SpecialMemberDecl, 4> SpecialMembersBeingDeclared;
 
   void NoteDeletedInheritingConstructor(CXXConstructorDecl *CD);
 
   void ActOnDefaultCtorInitializers(Decl *CDtorDecl);
 
   typedef ProcessingContextState ParsingClassState;
   ParsingClassState PushParsingClass() {
     ParsingClassDepth++;
     return DelayedDiagnostics.pushUndelayed();
   }
   void PopParsingClass(ParsingClassState state) {
     ParsingClassDepth--;
     DelayedDiagnostics.popUndelayed(state);
   }
 
   ValueDecl *tryLookupCtorInitMemberDecl(CXXRecordDecl *ClassDecl,
                                          CXXScopeSpec &SS,
                                          ParsedType TemplateTypeTy,
                                          IdentifierInfo *MemberOrBase);
 
 private:
   void setupImplicitSpecialMemberType(CXXMethodDecl *SpecialMem,
                                       QualType ResultTy,
                                       ArrayRef<QualType> Args);
 
   // A cache representing if we've fully checked the various comparison category
   // types stored in ASTContext. The bit-index corresponds to the integer value
   // of a ComparisonCategoryType enumerator.
   llvm::SmallBitVector FullyCheckedComparisonCategories;
 
   /// Check if there is a field shadowing.
   void CheckShadowInheritedFields(const SourceLocation &Loc,
                                   DeclarationName FieldName,
                                   const CXXRecordDecl *RD,
                                   bool DeclIsField = true);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Exception Specifications
   /// Implementations are in SemaExceptionSpec.cpp
   ///@{
 
 public:
   /// All the overriding functions seen during a class definition
   /// that had their exception spec checks delayed, plus the overridden
   /// function.
   SmallVector<std::pair<const CXXMethodDecl *, const CXXMethodDecl *>, 2>
       DelayedOverridingExceptionSpecChecks;
 
   /// All the function redeclarations seen during a class definition that had
   /// their exception spec checks delayed, plus the prior declaration they
   /// should be checked against. Except during error recovery, the new decl
   /// should always be a friend declaration, as that's the only valid way to
   /// redeclare a special member before its class is complete.
   SmallVector<std::pair<FunctionDecl *, FunctionDecl *>, 2>
       DelayedEquivalentExceptionSpecChecks;
 
   /// Determine if we're in a case where we need to (incorrectly) eagerly
   /// parse an exception specification to work around a libstdc++ bug.
   bool isLibstdcxxEagerExceptionSpecHack(const Declarator &D);
 
   /// Check the given noexcept-specifier, convert its expression, and compute
   /// the appropriate ExceptionSpecificationType.
   ExprResult ActOnNoexceptSpec(Expr *NoexceptExpr,
                                ExceptionSpecificationType &EST);
 
   CanThrowResult canThrow(const Stmt *E);
   /// Determine whether the callee of a particular function call can throw.
   /// E, D and Loc are all optional.
   static CanThrowResult canCalleeThrow(Sema &S, const Expr *E, const Decl *D,
                                        SourceLocation Loc = SourceLocation());
   const FunctionProtoType *ResolveExceptionSpec(SourceLocation Loc,
                                                 const FunctionProtoType *FPT);
   void UpdateExceptionSpec(FunctionDecl *FD,
                            const FunctionProtoType::ExceptionSpecInfo &ESI);
 
   /// CheckSpecifiedExceptionType - Check if the given type is valid in an
   /// exception specification. Incomplete types, or pointers to incomplete types
   /// other than void are not allowed.
   ///
   /// \param[in,out] T  The exception type. This will be decayed to a pointer
   /// type
   ///                   when the input is an array or a function type.
   bool CheckSpecifiedExceptionType(QualType &T, SourceRange Range);
 
   /// CheckDistantExceptionSpec - Check if the given type is a pointer or
   /// pointer to member to a function with an exception specification. This
   /// means that it is invalid to add another level of indirection.
   bool CheckDistantExceptionSpec(QualType T);
   bool CheckEquivalentExceptionSpec(FunctionDecl *Old, FunctionDecl *New);
 
   /// CheckEquivalentExceptionSpec - Check if the two types have equivalent
   /// exception specifications. Exception specifications are equivalent if
   /// they allow exactly the same set of exception types. It does not matter how
   /// that is achieved. See C++ [except.spec]p2.
   bool CheckEquivalentExceptionSpec(const FunctionProtoType *Old,
                                     SourceLocation OldLoc,
                                     const FunctionProtoType *New,
                                     SourceLocation NewLoc);
   bool CheckEquivalentExceptionSpec(const PartialDiagnostic &DiagID,
                                     const PartialDiagnostic &NoteID,
                                     const FunctionProtoType *Old,
                                     SourceLocation OldLoc,
                                     const FunctionProtoType *New,
                                     SourceLocation NewLoc);
   bool handlerCanCatch(QualType HandlerType, QualType ExceptionType);
 
   /// CheckExceptionSpecSubset - Check whether the second function type's
   /// exception specification is a subset (or equivalent) of the first function
   /// type. This is used by override and pointer assignment checks.
   bool CheckExceptionSpecSubset(
       const PartialDiagnostic &DiagID, const PartialDiagnostic &NestedDiagID,
       const PartialDiagnostic &NoteID, const PartialDiagnostic &NoThrowDiagID,
       const FunctionProtoType *Superset, bool SkipSupersetFirstParameter,
       SourceLocation SuperLoc, const FunctionProtoType *Subset,
       bool SkipSubsetFirstParameter, SourceLocation SubLoc);
 
   /// CheckParamExceptionSpec - Check if the parameter and return types of the
   /// two functions have equivalent exception specs. This is part of the
   /// assignment and override compatibility check. We do not check the
   /// parameters of parameter function pointers recursively, as no sane
   /// programmer would even be able to write such a function type.
   bool CheckParamExceptionSpec(
       const PartialDiagnostic &NestedDiagID, const PartialDiagnostic &NoteID,
       const FunctionProtoType *Target, bool SkipTargetFirstParameter,
       SourceLocation TargetLoc, const FunctionProtoType *Source,
       bool SkipSourceFirstParameter, SourceLocation SourceLoc);
 
   bool CheckExceptionSpecCompatibility(Expr *From, QualType ToType);
 
   /// CheckOverridingFunctionExceptionSpec - Checks whether the exception
   /// spec is a subset of base spec.
   bool CheckOverridingFunctionExceptionSpec(const CXXMethodDecl *New,
                                             const CXXMethodDecl *Old);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Expressions
   /// Implementations are in SemaExpr.cpp
   ///@{
 
 public:
   /// Describes how the expressions currently being parsed are
   /// evaluated at run-time, if at all.
   enum class ExpressionEvaluationContext {
     /// The current expression and its subexpressions occur within an
     /// unevaluated operand (C++11 [expr]p7), such as the subexpression of
     /// \c sizeof, where the type of the expression may be significant but
     /// no code will be generated to evaluate the value of the expression at
     /// run time.
     Unevaluated,
 
     /// The current expression occurs within a braced-init-list within
     /// an unevaluated operand. This is mostly like a regular unevaluated
     /// context, except that we still instantiate constexpr functions that are
     /// referenced here so that we can perform narrowing checks correctly.
     UnevaluatedList,
 
     /// The current expression occurs within a discarded statement.
     /// This behaves largely similarly to an unevaluated operand in preventing
     /// definitions from being required, but not in other ways.
     DiscardedStatement,
 
     /// The current expression occurs within an unevaluated
     /// operand that unconditionally permits abstract references to
     /// fields, such as a SIZE operator in MS-style inline assembly.
     UnevaluatedAbstract,
 
     /// The current context is "potentially evaluated" in C++11 terms,
     /// but the expression is evaluated at compile-time (like the values of
     /// cases in a switch statement).
     ConstantEvaluated,
 
     /// In addition of being constant evaluated, the current expression
     /// occurs in an immediate function context - either a consteval function
     /// or a consteval if statement.
     ImmediateFunctionContext,
 
     /// The current expression is potentially evaluated at run time,
     /// which means that code may be generated to evaluate the value of the
     /// expression at run time.
     PotentiallyEvaluated,
 
     /// The current expression is potentially evaluated, but any
     /// declarations referenced inside that expression are only used if
     /// in fact the current expression is used.
     ///
     /// This value is used when parsing default function arguments, for which
     /// we would like to provide diagnostics (e.g., passing non-POD arguments
     /// through varargs) but do not want to mark declarations as "referenced"
     /// until the default argument is used.
     PotentiallyEvaluatedIfUsed
   };
 
   /// Store a set of either DeclRefExprs or MemberExprs that contain a reference
   /// to a variable (constant) that may or may not be odr-used in this Expr, and
   /// we won't know until all lvalue-to-rvalue and discarded value conversions
   /// have been applied to all subexpressions of the enclosing full expression.
   /// This is cleared at the end of each full expression.
   using MaybeODRUseExprSet = llvm::SmallSetVector<Expr *, 4>;
   MaybeODRUseExprSet MaybeODRUseExprs;
 
   using ImmediateInvocationCandidate = llvm::PointerIntPair<ConstantExpr *, 1>;
 
   /// Data structure used to record current or nested
   /// expression evaluation contexts.
   struct ExpressionEvaluationContextRecord {
     /// The expression evaluation context.
     ExpressionEvaluationContext Context;
 
     /// Whether the enclosing context needed a cleanup.
     CleanupInfo ParentCleanup;
 
     /// The number of active cleanup objects when we entered
     /// this expression evaluation context.
     unsigned NumCleanupObjects;
 
     /// The number of typos encountered during this expression evaluation
     /// context (i.e. the number of TypoExprs created).
     unsigned NumTypos;
 
     MaybeODRUseExprSet SavedMaybeODRUseExprs;
 
     /// The lambdas that are present within this context, if it
     /// is indeed an unevaluated context.
     SmallVector<LambdaExpr *, 2> Lambdas;
 
     /// The declaration that provides context for lambda expressions
     /// and block literals if the normal declaration context does not
     /// suffice, e.g., in a default function argument.
     Decl *ManglingContextDecl;
 
     /// If we are processing a decltype type, a set of call expressions
     /// for which we have deferred checking the completeness of the return type.
     SmallVector<CallExpr *, 8> DelayedDecltypeCalls;
 
     /// If we are processing a decltype type, a set of temporary binding
     /// expressions for which we have deferred checking the destructor.
     SmallVector<CXXBindTemporaryExpr *, 8> DelayedDecltypeBinds;
 
     llvm::SmallPtrSet<const Expr *, 8> PossibleDerefs;
 
     /// Expressions appearing as the LHS of a volatile assignment in this
     /// context. We produce a warning for these when popping the context if
     /// they are not discarded-value expressions nor unevaluated operands.
     SmallVector<Expr *, 2> VolatileAssignmentLHSs;
 
     /// Set of candidates for starting an immediate invocation.
     llvm::SmallVector<ImmediateInvocationCandidate, 4>
         ImmediateInvocationCandidates;
 
     /// Set of DeclRefExprs referencing a consteval function when used in a
     /// context not already known to be immediately invoked.
     llvm::SmallPtrSet<DeclRefExpr *, 4> ReferenceToConsteval;
 
     /// P2718R0 - Lifetime extension in range-based for loops.
     /// MaterializeTemporaryExprs in for-range-init expressions which need to
     /// extend lifetime. Add MaterializeTemporaryExpr* if the value of
     /// InLifetimeExtendingContext is true.
     SmallVector<MaterializeTemporaryExpr *, 8> ForRangeLifetimeExtendTemps;
 
     /// \brief Describes whether we are in an expression constext which we have
     /// to handle differently.
     enum ExpressionKind {
       EK_Decltype,
       EK_TemplateArgument,
       EK_AttrArgument,
       EK_Other
     } ExprContext;
 
     // A context can be nested in both a discarded statement context and
     // an immediate function context, so they need to be tracked independently.
     bool InDiscardedStatement;
     bool InImmediateFunctionContext;
     bool InImmediateEscalatingFunctionContext;
 
     bool IsCurrentlyCheckingDefaultArgumentOrInitializer = false;
 
     // We are in a constant context, but we also allow
     // non constant expressions, for example for array bounds (which may be
     // VLAs).
     bool InConditionallyConstantEvaluateContext = false;
 
     /// Whether we are currently in a context in which all temporaries must be
     /// lifetime-extended, even if they're not bound to a reference (for
     /// example, in a for-range initializer).
     bool InLifetimeExtendingContext = false;
 
     /// Whether we should rebuild CXXDefaultArgExpr and CXXDefaultInitExpr.
     bool RebuildDefaultArgOrDefaultInit = false;
 
     // When evaluating immediate functions in the initializer of a default
     // argument or default member initializer, this is the declaration whose
     // default initializer is being evaluated and the location of the call
     // or constructor definition.
     struct InitializationContext {
       InitializationContext(SourceLocation Loc, ValueDecl *Decl,
                             DeclContext *Context)
           : Loc(Loc), Decl(Decl), Context(Context) {
         assert(Decl && Context && "invalid initialization context");
       }
 
       SourceLocation Loc;
       ValueDecl *Decl = nullptr;
       DeclContext *Context = nullptr;
     };
     std::optional<InitializationContext> DelayedDefaultInitializationContext;
 
     ExpressionEvaluationContextRecord(ExpressionEvaluationContext Context,
                                       unsigned NumCleanupObjects,
                                       CleanupInfo ParentCleanup,
                                       Decl *ManglingContextDecl,
                                       ExpressionKind ExprContext)
         : Context(Context), ParentCleanup(ParentCleanup),
           NumCleanupObjects(NumCleanupObjects), NumTypos(0),
           ManglingContextDecl(ManglingContextDecl), ExprContext(ExprContext),
           InDiscardedStatement(false), InImmediateFunctionContext(false),
           InImmediateEscalatingFunctionContext(false) {}
 
     bool isUnevaluated() const {
       return Context == ExpressionEvaluationContext::Unevaluated ||
              Context == ExpressionEvaluationContext::UnevaluatedAbstract ||
              Context == ExpressionEvaluationContext::UnevaluatedList;
     }
 
     bool isPotentiallyEvaluated() const {
       return Context == ExpressionEvaluationContext::PotentiallyEvaluated ||
              Context ==
                  ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed ||
              Context == ExpressionEvaluationContext::ConstantEvaluated;
     }
 
     bool isConstantEvaluated() const {
       return Context == ExpressionEvaluationContext::ConstantEvaluated ||
              Context == ExpressionEvaluationContext::ImmediateFunctionContext;
     }
 
     bool isImmediateFunctionContext() const {
       return Context == ExpressionEvaluationContext::ImmediateFunctionContext ||
              (Context == ExpressionEvaluationContext::DiscardedStatement &&
               InImmediateFunctionContext) ||
              // C++23 [expr.const]p14:
              // An expression or conversion is in an immediate function
              // context if it is potentially evaluated and either:
              //   * its innermost enclosing non-block scope is a function
              //     parameter scope of an immediate function, or
              //   * its enclosing statement is enclosed by the compound-
              //     statement of a consteval if statement.
              (Context == ExpressionEvaluationContext::PotentiallyEvaluated &&
               InImmediateFunctionContext);
     }
 
     bool isDiscardedStatementContext() const {
       return Context == ExpressionEvaluationContext::DiscardedStatement ||
              (Context ==
                   ExpressionEvaluationContext::ImmediateFunctionContext &&
               InDiscardedStatement);
     }
   };
 
   const ExpressionEvaluationContextRecord &currentEvaluationContext() const {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
     return ExprEvalContexts.back();
   };
 
   ExpressionEvaluationContextRecord &currentEvaluationContext() {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
     return ExprEvalContexts.back();
   };
 
   ExpressionEvaluationContextRecord &parentEvaluationContext() {
     assert(ExprEvalContexts.size() >= 2 &&
            "Must be in an expression evaluation context");
     return ExprEvalContexts[ExprEvalContexts.size() - 2];
   };
 
   const ExpressionEvaluationContextRecord &parentEvaluationContext() const {
     return const_cast<Sema *>(this)->parentEvaluationContext();
   };
 
   bool isAttrContext() const {
     return ExprEvalContexts.back().ExprContext ==
            ExpressionEvaluationContextRecord::ExpressionKind::EK_AttrArgument;
   }
 
   /// Increment when we find a reference; decrement when we find an ignored
   /// assignment.  Ultimately the value is 0 if every reference is an ignored
   /// assignment.
   llvm::DenseMap<const VarDecl *, int> RefsMinusAssignments;
 
   /// Used to control the generation of ExprWithCleanups.
   CleanupInfo Cleanup;
 
   /// ExprCleanupObjects - This is the stack of objects requiring
   /// cleanup that are created by the current full expression.
   SmallVector<ExprWithCleanups::CleanupObject, 8> ExprCleanupObjects;
 
   /// Determine whether the use of this declaration is valid, without
   /// emitting diagnostics.
   bool CanUseDecl(NamedDecl *D, bool TreatUnavailableAsInvalid);
   // A version of DiagnoseUseOfDecl that should be used if overload resolution
   // has been used to find this declaration, which means we don't have to bother
   // checking the trailing requires clause.
   bool DiagnoseUseOfOverloadedDecl(NamedDecl *D, SourceLocation Loc) {
     return DiagnoseUseOfDecl(
         D, Loc, /*UnknownObjCClass=*/nullptr, /*ObjCPropertyAccess=*/false,
         /*AvoidPartialAvailabilityChecks=*/false, /*ClassReceiver=*/nullptr,
         /*SkipTrailingRequiresClause=*/true);
   }
 
   /// Determine whether the use of this declaration is valid, and
   /// emit any corresponding diagnostics.
   ///
   /// This routine diagnoses various problems with referencing
   /// declarations that can occur when using a declaration. For example,
   /// it might warn if a deprecated or unavailable declaration is being
   /// used, or produce an error (and return true) if a C++0x deleted
   /// function is being used.
   ///
   /// \returns true if there was an error (this declaration cannot be
   /// referenced), false otherwise.
   bool DiagnoseUseOfDecl(NamedDecl *D, ArrayRef<SourceLocation> Locs,
                          const ObjCInterfaceDecl *UnknownObjCClass = nullptr,
                          bool ObjCPropertyAccess = false,
                          bool AvoidPartialAvailabilityChecks = false,
                          ObjCInterfaceDecl *ClassReciever = nullptr,
                          bool SkipTrailingRequiresClause = false);
 
   /// Emit a note explaining that this function is deleted.
   void NoteDeletedFunction(FunctionDecl *FD);
 
   /// DiagnoseSentinelCalls - This routine checks whether a call or
   /// message-send is to a declaration with the sentinel attribute, and
   /// if so, it checks that the requirements of the sentinel are
   /// satisfied.
   void DiagnoseSentinelCalls(const NamedDecl *D, SourceLocation Loc,
                              ArrayRef<Expr *> Args);
 
   void PushExpressionEvaluationContext(
       ExpressionEvaluationContext NewContext, Decl *LambdaContextDecl = nullptr,
       ExpressionEvaluationContextRecord::ExpressionKind Type =
           ExpressionEvaluationContextRecord::EK_Other);
   enum ReuseLambdaContextDecl_t { ReuseLambdaContextDecl };
   void PushExpressionEvaluationContext(
       ExpressionEvaluationContext NewContext, ReuseLambdaContextDecl_t,
       ExpressionEvaluationContextRecord::ExpressionKind Type =
           ExpressionEvaluationContextRecord::EK_Other);
   void PopExpressionEvaluationContext();
 
   void DiscardCleanupsInEvaluationContext();
 
   ExprResult TransformToPotentiallyEvaluated(Expr *E);
   TypeSourceInfo *TransformToPotentiallyEvaluated(TypeSourceInfo *TInfo);
   ExprResult HandleExprEvaluationContextForTypeof(Expr *E);
 
   /// Check whether E, which is either a discarded-value expression or an
   /// unevaluated operand, is a simple-assignment to a volatlie-qualified
   /// lvalue, and if so, remove it from the list of volatile-qualified
   /// assignments that we are going to warn are deprecated.
   void CheckUnusedVolatileAssignment(Expr *E);
 
   ExprResult ActOnConstantExpression(ExprResult Res);
 
   // Functions for marking a declaration referenced.  These functions also
   // contain the relevant logic for marking if a reference to a function or
   // variable is an odr-use (in the C++11 sense).  There are separate variants
   // for expressions referring to a decl; these exist because odr-use marking
   // needs to be delayed for some constant variables when we build one of the
   // named expressions.
   //
   // MightBeOdrUse indicates whether the use could possibly be an odr-use, and
   // should usually be true. This only needs to be set to false if the lack of
   // odr-use cannot be determined from the current context (for instance,
   // because the name denotes a virtual function and was written without an
   // explicit nested-name-specifier).
   void MarkAnyDeclReferenced(SourceLocation Loc, Decl *D, bool MightBeOdrUse);
 
   /// Mark a function referenced, and check whether it is odr-used
   /// (C++ [basic.def.odr]p2, C99 6.9p3)
   void MarkFunctionReferenced(SourceLocation Loc, FunctionDecl *Func,
                               bool MightBeOdrUse = true);
 
   /// Mark a variable referenced, and check whether it is odr-used
   /// (C++ [basic.def.odr]p2, C99 6.9p3).  Note that this should not be
   /// used directly for normal expressions referring to VarDecl.
   void MarkVariableReferenced(SourceLocation Loc, VarDecl *Var);
 
   /// Perform reference-marking and odr-use handling for a DeclRefExpr.
   ///
   /// Note, this may change the dependence of the DeclRefExpr, and so needs to
   /// be handled with care if the DeclRefExpr is not newly-created.
   void MarkDeclRefReferenced(DeclRefExpr *E, const Expr *Base = nullptr);
 
   /// Perform reference-marking and odr-use handling for a MemberExpr.
   void MarkMemberReferenced(MemberExpr *E);
 
   /// Perform reference-marking and odr-use handling for a FunctionParmPackExpr.
   void MarkFunctionParmPackReferenced(FunctionParmPackExpr *E);
   void MarkCaptureUsedInEnclosingContext(ValueDecl *Capture, SourceLocation Loc,
                                          unsigned CapturingScopeIndex);
 
   ExprResult CheckLValueToRValueConversionOperand(Expr *E);
   void CleanupVarDeclMarking();
 
   enum TryCaptureKind {
     TryCapture_Implicit,
     TryCapture_ExplicitByVal,
     TryCapture_ExplicitByRef
   };
 
   /// Try to capture the given variable.
   ///
   /// \param Var The variable to capture.
   ///
   /// \param Loc The location at which the capture occurs.
   ///
   /// \param Kind The kind of capture, which may be implicit (for either a
   /// block or a lambda), or explicit by-value or by-reference (for a lambda).
   ///
   /// \param EllipsisLoc The location of the ellipsis, if one is provided in
   /// an explicit lambda capture.
   ///
   /// \param BuildAndDiagnose Whether we are actually supposed to add the
   /// captures or diagnose errors. If false, this routine merely check whether
   /// the capture can occur without performing the capture itself or complaining
   /// if the variable cannot be captured.
   ///
   /// \param CaptureType Will be set to the type of the field used to capture
   /// this variable in the innermost block or lambda. Only valid when the
   /// variable can be captured.
   ///
   /// \param DeclRefType Will be set to the type of a reference to the capture
   /// from within the current scope. Only valid when the variable can be
   /// captured.
   ///
   /// \param FunctionScopeIndexToStopAt If non-null, it points to the index
   /// of the FunctionScopeInfo stack beyond which we do not attempt to capture.
   /// This is useful when enclosing lambdas must speculatively capture
   /// variables that may or may not be used in certain specializations of
   /// a nested generic lambda.
   ///
   /// \returns true if an error occurred (i.e., the variable cannot be
   /// captured) and false if the capture succeeded.
   bool tryCaptureVariable(ValueDecl *Var, SourceLocation Loc,
                           TryCaptureKind Kind, SourceLocation EllipsisLoc,
                           bool BuildAndDiagnose, QualType &CaptureType,
                           QualType &DeclRefType,
                           const unsigned *const FunctionScopeIndexToStopAt);
 
   /// Try to capture the given variable.
   bool tryCaptureVariable(ValueDecl *Var, SourceLocation Loc,
                           TryCaptureKind Kind = TryCapture_Implicit,
                           SourceLocation EllipsisLoc = SourceLocation());
 
   /// Checks if the variable must be captured.
   bool NeedToCaptureVariable(ValueDecl *Var, SourceLocation Loc);
 
   /// Given a variable, determine the type that a reference to that
   /// variable will have in the given scope.
   QualType getCapturedDeclRefType(ValueDecl *Var, SourceLocation Loc);
 
   /// Mark all of the declarations referenced within a particular AST node as
   /// referenced. Used when template instantiation instantiates a non-dependent
   /// type -- entities referenced by the type are now referenced.
   void MarkDeclarationsReferencedInType(SourceLocation Loc, QualType T);
 
   /// Mark any declarations that appear within this expression or any
   /// potentially-evaluated subexpressions as "referenced".
   ///
   /// \param SkipLocalVariables If true, don't mark local variables as
   /// 'referenced'.
   /// \param StopAt Subexpressions that we shouldn't recurse into.
   void MarkDeclarationsReferencedInExpr(Expr *E,
                                         bool SkipLocalVariables = false,
                                         ArrayRef<const Expr *> StopAt = {});
 
   /// Try to convert an expression \p E to type \p Ty. Returns the result of the
   /// conversion.
   ExprResult tryConvertExprToType(Expr *E, QualType Ty);
 
   /// Conditionally issue a diagnostic based on the statements's reachability
   /// analysis.
   ///
   /// \param Stmts If Stmts is non-empty, delay reporting the diagnostic until
   /// the function body is parsed, and then do a basic reachability analysis to
   /// determine if the statement is reachable. If it is unreachable, the
   /// diagnostic will not be emitted.
   bool DiagIfReachable(SourceLocation Loc, ArrayRef<const Stmt *> Stmts,
                        const PartialDiagnostic &PD);
 
   /// Conditionally issue a diagnostic based on the current
   /// evaluation context.
   ///
   /// \param Statement If Statement is non-null, delay reporting the
   /// diagnostic until the function body is parsed, and then do a basic
   /// reachability analysis to determine if the statement is reachable.
   /// If it is unreachable, the diagnostic will not be emitted.
   bool DiagRuntimeBehavior(SourceLocation Loc, const Stmt *Statement,
                            const PartialDiagnostic &PD);
   /// Similar, but diagnostic is only produced if all the specified statements
   /// are reachable.
   bool DiagRuntimeBehavior(SourceLocation Loc, ArrayRef<const Stmt *> Stmts,
                            const PartialDiagnostic &PD);
 
   // Primary Expressions.
   SourceRange getExprRange(Expr *E) const;
 
   ExprResult ActOnIdExpression(Scope *S, CXXScopeSpec &SS,
                                SourceLocation TemplateKWLoc, UnqualifiedId &Id,
                                bool HasTrailingLParen, bool IsAddressOfOperand,
                                CorrectionCandidateCallback *CCC = nullptr,
                                bool IsInlineAsmIdentifier = false,
                                Token *KeywordReplacement = nullptr);
 
   /// Decomposes the given name into a DeclarationNameInfo, its location, and
   /// possibly a list of template arguments.
   ///
   /// If this produces template arguments, it is permitted to call
   /// DecomposeTemplateName.
   ///
   /// This actually loses a lot of source location information for
   /// non-standard name kinds; we should consider preserving that in
   /// some way.
   void DecomposeUnqualifiedId(const UnqualifiedId &Id,
                               TemplateArgumentListInfo &Buffer,
                               DeclarationNameInfo &NameInfo,
                               const TemplateArgumentListInfo *&TemplateArgs);
 
   /// Diagnose a lookup that found results in an enclosing class during error
   /// recovery. This usually indicates that the results were found in a
   /// dependent base class that could not be searched as part of a template
   /// definition. Always issues a diagnostic (though this may be only a warning
   /// in MS compatibility mode).
   ///
   /// Return \c true if the error is unrecoverable, or \c false if the caller
   /// should attempt to recover using these lookup results.
   bool DiagnoseDependentMemberLookup(const LookupResult &R);
 
   /// Diagnose an empty lookup.
   ///
   /// \return false if new lookup candidates were found
   bool
   DiagnoseEmptyLookup(Scope *S, CXXScopeSpec &SS, LookupResult &R,
                       CorrectionCandidateCallback &CCC,
                       TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr,
                       ArrayRef<Expr *> Args = {},
                       DeclContext *LookupCtx = nullptr,
                       TypoExpr **Out = nullptr);
 
   /// If \p D cannot be odr-used in the current expression evaluation context,
   /// return a reason explaining why. Otherwise, return NOUR_None.
   NonOdrUseReason getNonOdrUseReasonInCurrentContext(ValueDecl *D);
 
   DeclRefExpr *BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                                 SourceLocation Loc,
                                 const CXXScopeSpec *SS = nullptr);
   DeclRefExpr *
   BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                    const DeclarationNameInfo &NameInfo,
                    const CXXScopeSpec *SS = nullptr,
                    NamedDecl *FoundD = nullptr,
                    SourceLocation TemplateKWLoc = SourceLocation(),
                    const TemplateArgumentListInfo *TemplateArgs = nullptr);
 
   /// BuildDeclRefExpr - Build an expression that references a
   /// declaration that does not require a closure capture.
   DeclRefExpr *
   BuildDeclRefExpr(ValueDecl *D, QualType Ty, ExprValueKind VK,
                    const DeclarationNameInfo &NameInfo,
                    NestedNameSpecifierLoc NNS, NamedDecl *FoundD = nullptr,
                    SourceLocation TemplateKWLoc = SourceLocation(),
                    const TemplateArgumentListInfo *TemplateArgs = nullptr);
 
   bool UseArgumentDependentLookup(const CXXScopeSpec &SS, const LookupResult &R,
                                   bool HasTrailingLParen);
 
   /// BuildQualifiedDeclarationNameExpr - Build a C++ qualified
   /// declaration name, generally during template instantiation.
   /// There's a large number of things which don't need to be done along
   /// this path.
   ExprResult BuildQualifiedDeclarationNameExpr(
       CXXScopeSpec &SS, const DeclarationNameInfo &NameInfo,
       bool IsAddressOfOperand, TypeSourceInfo **RecoveryTSI = nullptr);
 
   ExprResult BuildDeclarationNameExpr(const CXXScopeSpec &SS, LookupResult &R,
                                       bool NeedsADL,
                                       bool AcceptInvalidDecl = false);
 
   /// Complete semantic analysis for a reference to the given declaration.
   ExprResult BuildDeclarationNameExpr(
       const CXXScopeSpec &SS, const DeclarationNameInfo &NameInfo, NamedDecl *D,
       NamedDecl *FoundD = nullptr,
       const TemplateArgumentListInfo *TemplateArgs = nullptr,
       bool AcceptInvalidDecl = false);
 
   // ExpandFunctionLocalPredefinedMacros - Returns a new vector of Tokens,
   // where Tokens representing function local predefined macros (such as
   // __FUNCTION__) are replaced (expanded) with string-literal Tokens.
   std::vector<Token> ExpandFunctionLocalPredefinedMacros(ArrayRef<Token> Toks);
 
   ExprResult BuildPredefinedExpr(SourceLocation Loc, PredefinedIdentKind IK);
   ExprResult ActOnPredefinedExpr(SourceLocation Loc, tok::TokenKind Kind);
   ExprResult ActOnIntegerConstant(SourceLocation Loc, int64_t Val);
 
   bool CheckLoopHintExpr(Expr *E, SourceLocation Loc, bool AllowZero);
 
   ExprResult ActOnNumericConstant(const Token &Tok, Scope *UDLScope = nullptr);
   ExprResult ActOnCharacterConstant(const Token &Tok,
                                     Scope *UDLScope = nullptr);
   ExprResult ActOnParenExpr(SourceLocation L, SourceLocation R, Expr *E);
   ExprResult ActOnParenListExpr(SourceLocation L, SourceLocation R,
                                 MultiExprArg Val);
 
   /// ActOnStringLiteral - The specified tokens were lexed as pasted string
   /// fragments (e.g. "foo" "bar" L"baz").  The result string has to handle
   /// string concatenation ([C99 5.1.1.2, translation phase #6]), so it may come
   /// from multiple tokens.  However, the common case is that StringToks points
   /// to one string.
   ExprResult ActOnStringLiteral(ArrayRef<Token> StringToks,
                                 Scope *UDLScope = nullptr);
 
   ExprResult ActOnUnevaluatedStringLiteral(ArrayRef<Token> StringToks);
 
   /// ControllingExprOrType is either an opaque pointer coming out of a
   /// ParsedType or an Expr *. FIXME: it'd be better to split this interface
   /// into two so we don't take a void *, but that's awkward because one of
   /// the operands is either a ParsedType or an Expr *, which doesn't lend
   /// itself to generic code very well.
   ExprResult ActOnGenericSelectionExpr(SourceLocation KeyLoc,
                                        SourceLocation DefaultLoc,
                                        SourceLocation RParenLoc,
                                        bool PredicateIsExpr,
                                        void *ControllingExprOrType,
                                        ArrayRef<ParsedType> ArgTypes,
                                        ArrayRef<Expr *> ArgExprs);
   /// ControllingExprOrType is either a TypeSourceInfo * or an Expr *. FIXME:
   /// it'd be better to split this interface into two so we don't take a
   /// void *, but see the FIXME on ActOnGenericSelectionExpr as to why that
   /// isn't a trivial change.
   ExprResult CreateGenericSelectionExpr(SourceLocation KeyLoc,
                                         SourceLocation DefaultLoc,
                                         SourceLocation RParenLoc,
                                         bool PredicateIsExpr,
                                         void *ControllingExprOrType,
                                         ArrayRef<TypeSourceInfo *> Types,
                                         ArrayRef<Expr *> Exprs);
 
   // Binary/Unary Operators.  'Tok' is the token for the operator.
   ExprResult CreateBuiltinUnaryOp(SourceLocation OpLoc, UnaryOperatorKind Opc,
                                   Expr *InputExpr, bool IsAfterAmp = false);
   ExprResult BuildUnaryOp(Scope *S, SourceLocation OpLoc, UnaryOperatorKind Opc,
                           Expr *Input, bool IsAfterAmp = false);
 
   /// Unary Operators.  'Tok' is the token for the operator.
   ExprResult ActOnUnaryOp(Scope *S, SourceLocation OpLoc, tok::TokenKind Op,
                           Expr *Input, bool IsAfterAmp = false);
 
   /// Determine whether the given expression is a qualified member
   /// access expression, of a form that could be turned into a pointer to member
   /// with the address-of operator.
   bool isQualifiedMemberAccess(Expr *E);
   bool CheckUseOfCXXMethodAsAddressOfOperand(SourceLocation OpLoc,
                                              const Expr *Op,
                                              const CXXMethodDecl *MD);
 
   /// CheckAddressOfOperand - The operand of & must be either a function
   /// designator or an lvalue designating an object. If it is an lvalue, the
   /// object cannot be declared with storage class register or be a bit field.
   /// Note: The usual conversions are *not* applied to the operand of the &
   /// operator (C99 6.3.2.1p[2-4]), and its result is never an lvalue.
   /// In C++, the operand might be an overloaded function name, in which case
   /// we allow the '&' but retain the overloaded-function type.
   QualType CheckAddressOfOperand(ExprResult &Operand, SourceLocation OpLoc);
 
   /// ActOnAlignasTypeArgument - Handle @c alignas(type-id) and @c
   /// _Alignas(type-name) .
   /// [dcl.align] An alignment-specifier of the form
   /// alignas(type-id) has the same effect as alignas(alignof(type-id)).
   ///
   /// [N1570 6.7.5] _Alignas(type-name) is equivalent to
   /// _Alignas(_Alignof(type-name)).
   bool ActOnAlignasTypeArgument(StringRef KWName, ParsedType Ty,
                                 SourceLocation OpLoc, SourceRange R);
   bool CheckAlignasTypeArgument(StringRef KWName, TypeSourceInfo *TInfo,
                                 SourceLocation OpLoc, SourceRange R);
 
   /// Build a sizeof or alignof expression given a type operand.
   ExprResult CreateUnaryExprOrTypeTraitExpr(TypeSourceInfo *TInfo,
                                             SourceLocation OpLoc,
                                             UnaryExprOrTypeTrait ExprKind,
                                             SourceRange R);
 
   /// Build a sizeof or alignof expression given an expression
   /// operand.
   ExprResult CreateUnaryExprOrTypeTraitExpr(Expr *E, SourceLocation OpLoc,
                                             UnaryExprOrTypeTrait ExprKind);
 
   /// ActOnUnaryExprOrTypeTraitExpr - Handle @c sizeof(type) and @c sizeof @c
   /// expr and the same for @c alignof and @c __alignof
   /// Note that the ArgRange is invalid if isType is false.
   ExprResult ActOnUnaryExprOrTypeTraitExpr(SourceLocation OpLoc,
                                            UnaryExprOrTypeTrait ExprKind,
                                            bool IsType, void *TyOrEx,
                                            SourceRange ArgRange);
 
   /// Check for operands with placeholder types and complain if found.
   /// Returns ExprError() if there was an error and no recovery was possible.
   ExprResult CheckPlaceholderExpr(Expr *E);
   bool CheckVecStepExpr(Expr *E);
 
   /// Check the constraints on expression operands to unary type expression
   /// and type traits.
   ///
   /// Completes any types necessary and validates the constraints on the operand
   /// expression. The logic mostly mirrors the type-based overload, but may
   /// modify the expression as it completes the type for that expression through
   /// template instantiation, etc.
   bool CheckUnaryExprOrTypeTraitOperand(Expr *E, UnaryExprOrTypeTrait ExprKind);
 
   /// Check the constraints on operands to unary expression and type
   /// traits.
   ///
   /// This will complete any types necessary, and validate the various
   /// constraints on those operands.
   ///
   /// The UsualUnaryConversions() function is *not* called by this routine.
   /// C99 6.3.2.1p[2-4] all state:
   ///   Except when it is the operand of the sizeof operator ...
   ///
   /// C++ [expr.sizeof]p4
   ///   The lvalue-to-rvalue, array-to-pointer, and function-to-pointer
   ///   standard conversions are not applied to the operand of sizeof.
   ///
   /// This policy is followed for all of the unary trait expressions.
   bool CheckUnaryExprOrTypeTraitOperand(QualType ExprType, SourceLocation OpLoc,
                                         SourceRange ExprRange,
                                         UnaryExprOrTypeTrait ExprKind,
                                         StringRef KWName);
 
   ExprResult ActOnPostfixUnaryOp(Scope *S, SourceLocation OpLoc,
                                  tok::TokenKind Kind, Expr *Input);
 
   ExprResult ActOnArraySubscriptExpr(Scope *S, Expr *Base, SourceLocation LLoc,
                                      MultiExprArg ArgExprs,
                                      SourceLocation RLoc);
   ExprResult CreateBuiltinArraySubscriptExpr(Expr *Base, SourceLocation LLoc,
                                              Expr *Idx, SourceLocation RLoc);
 
   ExprResult CreateBuiltinMatrixSubscriptExpr(Expr *Base, Expr *RowIdx,
                                               Expr *ColumnIdx,
                                               SourceLocation RBLoc);
 
   /// ConvertArgumentsForCall - Converts the arguments specified in
   /// Args/NumArgs to the parameter types of the function FDecl with
   /// function prototype Proto. Call is the call expression itself, and
   /// Fn is the function expression. For a C++ member function, this
   /// routine does not attempt to convert the object argument. Returns
   /// true if the call is ill-formed.
   bool ConvertArgumentsForCall(CallExpr *Call, Expr *Fn, FunctionDecl *FDecl,
                                const FunctionProtoType *Proto,
                                ArrayRef<Expr *> Args, SourceLocation RParenLoc,
                                bool ExecConfig = false);
 
   /// CheckStaticArrayArgument - If the given argument corresponds to a static
   /// array parameter, check that it is non-null, and that if it is formed by
   /// array-to-pointer decay, the underlying array is sufficiently large.
   ///
   /// C99 6.7.5.3p7: If the keyword static also appears within the [ and ] of
   /// the array type derivation, then for each call to the function, the value
   /// of the corresponding actual argument shall provide access to the first
   /// element of an array with at least as many elements as specified by the
   /// size expression.
   void CheckStaticArrayArgument(SourceLocation CallLoc, ParmVarDecl *Param,
                                 const Expr *ArgExpr);
 
   /// ActOnCallExpr - Handle a call to Fn with the specified array of arguments.
   /// This provides the location of the left/right parens and a list of comma
   /// locations.
   ExprResult ActOnCallExpr(Scope *S, Expr *Fn, SourceLocation LParenLoc,
                            MultiExprArg ArgExprs, SourceLocation RParenLoc,
                            Expr *ExecConfig = nullptr);
 
   /// BuildCallExpr - Handle a call to Fn with the specified array of arguments.
   /// This provides the location of the left/right parens and a list of comma
   /// locations.
   ExprResult BuildCallExpr(Scope *S, Expr *Fn, SourceLocation LParenLoc,
                            MultiExprArg ArgExprs, SourceLocation RParenLoc,
                            Expr *ExecConfig = nullptr,
                            bool IsExecConfig = false,
                            bool AllowRecovery = false);
 
   /// BuildBuiltinCallExpr - Create a call to a builtin function specified by Id
   //  with the specified CallArgs
   Expr *BuildBuiltinCallExpr(SourceLocation Loc, Builtin::ID Id,
                              MultiExprArg CallArgs);
 
   using ADLCallKind = CallExpr::ADLCallKind;
 
   /// BuildResolvedCallExpr - Build a call to a resolved expression,
   /// i.e. an expression not of \p OverloadTy.  The expression should
   /// unary-convert to an expression of function-pointer or
   /// block-pointer type.
   ///
   /// \param NDecl the declaration being called, if available
   ExprResult
   BuildResolvedCallExpr(Expr *Fn, NamedDecl *NDecl, SourceLocation LParenLoc,
                         ArrayRef<Expr *> Arg, SourceLocation RParenLoc,
                         Expr *Config = nullptr, bool IsExecConfig = false,
                         ADLCallKind UsesADL = ADLCallKind::NotADL);
 
   ExprResult ActOnCastExpr(Scope *S, SourceLocation LParenLoc, Declarator &D,
                            ParsedType &Ty, SourceLocation RParenLoc,
                            Expr *CastExpr);
 
   /// Prepares for a scalar cast, performing all the necessary stages
   /// except the final cast and returning the kind required.
   CastKind PrepareScalarCast(ExprResult &src, QualType destType);
 
   /// Build an altivec or OpenCL literal.
   ExprResult BuildVectorLiteral(SourceLocation LParenLoc,
                                 SourceLocation RParenLoc, Expr *E,
                                 TypeSourceInfo *TInfo);
 
   /// This is not an AltiVec-style cast or or C++ direct-initialization, so turn
   /// the ParenListExpr into a sequence of comma binary operators.
   ExprResult MaybeConvertParenListExprToParenExpr(Scope *S, Expr *ME);
 
   ExprResult ActOnCompoundLiteral(SourceLocation LParenLoc, ParsedType Ty,
                                   SourceLocation RParenLoc, Expr *InitExpr);
 
   ExprResult BuildCompoundLiteralExpr(SourceLocation LParenLoc,
                                       TypeSourceInfo *TInfo,
                                       SourceLocation RParenLoc,
                                       Expr *LiteralExpr);
 
   ExprResult ActOnInitList(SourceLocation LBraceLoc, MultiExprArg InitArgList,
                            SourceLocation RBraceLoc);
 
   ExprResult BuildInitList(SourceLocation LBraceLoc, MultiExprArg InitArgList,
                            SourceLocation RBraceLoc);
 
   /// Binary Operators.  'Tok' is the token for the operator.
   ExprResult ActOnBinOp(Scope *S, SourceLocation TokLoc, tok::TokenKind Kind,
                         Expr *LHSExpr, Expr *RHSExpr);
   ExprResult BuildBinOp(Scope *S, SourceLocation OpLoc, BinaryOperatorKind Opc,
                         Expr *LHSExpr, Expr *RHSExpr);
 
   /// CreateBuiltinBinOp - Creates a new built-in binary operation with
   /// operator @p Opc at location @c TokLoc. This routine only supports
   /// built-in operations; ActOnBinOp handles overloaded operators.
   ExprResult CreateBuiltinBinOp(SourceLocation OpLoc, BinaryOperatorKind Opc,
                                 Expr *LHSExpr, Expr *RHSExpr);
   void LookupBinOp(Scope *S, SourceLocation OpLoc, BinaryOperatorKind Opc,
                    UnresolvedSetImpl &Functions);
 
   /// Look for instances where it is likely the comma operator is confused with
   /// another operator.  There is an explicit list of acceptable expressions for
   /// the left hand side of the comma operator, otherwise emit a warning.
   void DiagnoseCommaOperator(const Expr *LHS, SourceLocation Loc);
 
   /// ActOnConditionalOp - Parse a ?: operation.  Note that 'LHS' may be null
   /// in the case of a the GNU conditional expr extension.
   ExprResult ActOnConditionalOp(SourceLocation QuestionLoc,
                                 SourceLocation ColonLoc, Expr *CondExpr,
                                 Expr *LHSExpr, Expr *RHSExpr);
 
   /// ActOnAddrLabel - Parse the GNU address of label extension: "&&foo".
   ExprResult ActOnAddrLabel(SourceLocation OpLoc, SourceLocation LabLoc,
                             LabelDecl *TheDecl);
 
   void ActOnStartStmtExpr();
   ExprResult ActOnStmtExpr(Scope *S, SourceLocation LPLoc, Stmt *SubStmt,
                            SourceLocation RPLoc);
   ExprResult BuildStmtExpr(SourceLocation LPLoc, Stmt *SubStmt,
                            SourceLocation RPLoc, unsigned TemplateDepth);
   // Handle the final expression in a statement expression.
   ExprResult ActOnStmtExprResult(ExprResult E);
   void ActOnStmtExprError();
 
   // __builtin_offsetof(type, identifier(.identifier|[expr])*)
   struct OffsetOfComponent {
     SourceLocation LocStart, LocEnd;
     bool isBrackets; // true if [expr], false if .ident
     union {
       IdentifierInfo *IdentInfo;
       Expr *E;
     } U;
   };
 
   /// __builtin_offsetof(type, a.b[123][456].c)
   ExprResult BuildBuiltinOffsetOf(SourceLocation BuiltinLoc,
                                   TypeSourceInfo *TInfo,
                                   ArrayRef<OffsetOfComponent> Components,
                                   SourceLocation RParenLoc);
   ExprResult ActOnBuiltinOffsetOf(Scope *S, SourceLocation BuiltinLoc,
                                   SourceLocation TypeLoc,
                                   ParsedType ParsedArgTy,
                                   ArrayRef<OffsetOfComponent> Components,
                                   SourceLocation RParenLoc);
 
   // __builtin_choose_expr(constExpr, expr1, expr2)
   ExprResult ActOnChooseExpr(SourceLocation BuiltinLoc, Expr *CondExpr,
                              Expr *LHSExpr, Expr *RHSExpr,
                              SourceLocation RPLoc);
 
   // __builtin_va_arg(expr, type)
   ExprResult ActOnVAArg(SourceLocation BuiltinLoc, Expr *E, ParsedType Ty,
                         SourceLocation RPLoc);
   ExprResult BuildVAArgExpr(SourceLocation BuiltinLoc, Expr *E,
                             TypeSourceInfo *TInfo, SourceLocation RPLoc);
 
   // __builtin_LINE(), __builtin_FUNCTION(), __builtin_FUNCSIG(),
   // __builtin_FILE(), __builtin_COLUMN(), __builtin_source_location()
   ExprResult ActOnSourceLocExpr(SourceLocIdentKind Kind,
                                 SourceLocation BuiltinLoc,
                                 SourceLocation RPLoc);
 
   // #embed
   ExprResult ActOnEmbedExpr(SourceLocation EmbedKeywordLoc,
                             StringLiteral *BinaryData);
 
   // Build a potentially resolved SourceLocExpr.
   ExprResult BuildSourceLocExpr(SourceLocIdentKind Kind, QualType ResultTy,
                                 SourceLocation BuiltinLoc, SourceLocation RPLoc,
                                 DeclContext *ParentContext);
 
   // __null
   ExprResult ActOnGNUNullExpr(SourceLocation TokenLoc);
 
   bool CheckCaseExpression(Expr *E);
 
   //===------------------------- "Block" Extension ------------------------===//
 
   /// ActOnBlockStart - This callback is invoked when a block literal is
   /// started.
   void ActOnBlockStart(SourceLocation CaretLoc, Scope *CurScope);
 
   /// ActOnBlockArguments - This callback allows processing of block arguments.
   /// If there are no arguments, this is still invoked.
   void ActOnBlockArguments(SourceLocation CaretLoc, Declarator &ParamInfo,
                            Scope *CurScope);
 
   /// ActOnBlockError - If there is an error parsing a block, this callback
   /// is invoked to pop the information about the block from the action impl.
   void ActOnBlockError(SourceLocation CaretLoc, Scope *CurScope);
 
   /// ActOnBlockStmtExpr - This is called when the body of a block statement
   /// literal was successfully completed.  ^(int x){...}
   ExprResult ActOnBlockStmtExpr(SourceLocation CaretLoc, Stmt *Body,
                                 Scope *CurScope);
 
   //===---------------------------- Clang Extensions ----------------------===//
 
   /// ActOnConvertVectorExpr - create a new convert-vector expression from the
   /// provided arguments.
   ///
   /// __builtin_convertvector( value, dst type )
   ///
   ExprResult ActOnConvertVectorExpr(Expr *E, ParsedType ParsedDestTy,
                                     SourceLocation BuiltinLoc,
                                     SourceLocation RParenLoc);
 
   //===---------------------------- OpenCL Features -----------------------===//
 
   /// Parse a __builtin_astype expression.
   ///
   /// __builtin_astype( value, dst type )
   ///
   ExprResult ActOnAsTypeExpr(Expr *E, ParsedType ParsedDestTy,
                              SourceLocation BuiltinLoc,
                              SourceLocation RParenLoc);
 
   /// Create a new AsTypeExpr node (bitcast) from the arguments.
   ExprResult BuildAsTypeExpr(Expr *E, QualType DestTy,
                              SourceLocation BuiltinLoc,
                              SourceLocation RParenLoc);
 
   /// Attempts to produce a RecoveryExpr after some AST node cannot be created.
   ExprResult CreateRecoveryExpr(SourceLocation Begin, SourceLocation End,
                                 ArrayRef<Expr *> SubExprs,
                                 QualType T = QualType());
 
   /// Cast a base object to a member's actual type.
   ///
   /// There are two relevant checks:
   ///
   /// C++ [class.access.base]p7:
   ///
   ///   If a class member access operator [...] is used to access a non-static
   ///   data member or non-static member function, the reference is ill-formed
   ///   if the left operand [...] cannot be implicitly converted to a pointer to
   ///   the naming class of the right operand.
   ///
   /// C++ [expr.ref]p7:
   ///
   ///   If E2 is a non-static data member or a non-static member function, the
   ///   program is ill-formed if the class of which E2 is directly a member is
   ///   an ambiguous base (11.8) of the naming class (11.9.3) of E2.
   ///
   /// Note that the latter check does not consider access; the access of the
   /// "real" base class is checked as appropriate when checking the access of
   /// the member name.
   ExprResult PerformObjectMemberConversion(Expr *From,
                                            NestedNameSpecifier *Qualifier,
                                            NamedDecl *FoundDecl,
                                            NamedDecl *Member);
 
   /// CheckCallReturnType - Checks that a call expression's return type is
   /// complete. Returns true on failure. The location passed in is the location
   /// that best represents the call.
   bool CheckCallReturnType(QualType ReturnType, SourceLocation Loc,
                            CallExpr *CE, FunctionDecl *FD);
 
   /// Emit a warning for all pending noderef expressions that we recorded.
   void WarnOnPendingNoDerefs(ExpressionEvaluationContextRecord &Rec);
 
   ExprResult BuildCXXDefaultInitExpr(SourceLocation Loc, FieldDecl *Field);
 
   /// Instantiate or parse a C++ default argument expression as necessary.
   /// Return true on error.
   bool CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
                               ParmVarDecl *Param, Expr *Init = nullptr,
                               bool SkipImmediateInvocations = true);
 
   /// BuildCXXDefaultArgExpr - Creates a CXXDefaultArgExpr, instantiating
   /// the default expr if needed.
   ExprResult BuildCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
                                     ParmVarDecl *Param, Expr *Init = nullptr);
 
   /// Wrap the expression in a ConstantExpr if it is a potential immediate
   /// invocation.
   ExprResult CheckForImmediateInvocation(ExprResult E, FunctionDecl *Decl);
 
   void MarkExpressionAsImmediateEscalating(Expr *E);
 
   // Check that the SME attributes for PSTATE.ZA and PSTATE.SM are compatible.
   bool IsInvalidSMECallConversion(QualType FromType, QualType ToType);
 
   /// Abstract base class used for diagnosing integer constant
   /// expression violations.
   class VerifyICEDiagnoser {
   public:
     bool Suppress;
 
     VerifyICEDiagnoser(bool Suppress = false) : Suppress(Suppress) {}
 
     virtual SemaDiagnosticBuilder
     diagnoseNotICEType(Sema &S, SourceLocation Loc, QualType T);
     virtual SemaDiagnosticBuilder diagnoseNotICE(Sema &S,
                                                  SourceLocation Loc) = 0;
     virtual SemaDiagnosticBuilder diagnoseFold(Sema &S, SourceLocation Loc);
     virtual ~VerifyICEDiagnoser() {}
   };
 
   enum AllowFoldKind {
     NoFold,
     AllowFold,
   };
 
   /// VerifyIntegerConstantExpression - Verifies that an expression is an ICE,
   /// and reports the appropriate diagnostics. Returns false on success.
   /// Can optionally return the value of the expression.
   ExprResult VerifyIntegerConstantExpression(Expr *E, llvm::APSInt *Result,
                                              VerifyICEDiagnoser &Diagnoser,
                                              AllowFoldKind CanFold = NoFold);
   ExprResult VerifyIntegerConstantExpression(Expr *E, llvm::APSInt *Result,
                                              unsigned DiagID,
                                              AllowFoldKind CanFold = NoFold);
   ExprResult VerifyIntegerConstantExpression(Expr *E,
                                              llvm::APSInt *Result = nullptr,
                                              AllowFoldKind CanFold = NoFold);
   ExprResult VerifyIntegerConstantExpression(Expr *E,
                                              AllowFoldKind CanFold = NoFold) {
     return VerifyIntegerConstantExpression(E, nullptr, CanFold);
   }
 
   /// DiagnoseAssignmentAsCondition - Given that an expression is
   /// being used as a boolean condition, warn if it's an assignment.
   void DiagnoseAssignmentAsCondition(Expr *E);
 
   /// Redundant parentheses over an equality comparison can indicate
   /// that the user intended an assignment used as condition.
   void DiagnoseEqualityWithExtraParens(ParenExpr *ParenE);
 
   class FullExprArg {
   public:
     FullExprArg() : E(nullptr) {}
     FullExprArg(Sema &actions) : E(nullptr) {}
 
     ExprResult release() { return E; }
 
     Expr *get() const { return E; }
 
     Expr *operator->() { return E; }
 
   private:
     // FIXME: No need to make the entire Sema class a friend when it's just
     // Sema::MakeFullExpr that needs access to the constructor below.
     friend class Sema;
 
     explicit FullExprArg(Expr *expr) : E(expr) {}
 
     Expr *E;
   };
 
   FullExprArg MakeFullExpr(Expr *Arg) {
     return MakeFullExpr(Arg, Arg ? Arg->getExprLoc() : SourceLocation());
   }
   FullExprArg MakeFullExpr(Expr *Arg, SourceLocation CC) {
     return FullExprArg(
         ActOnFinishFullExpr(Arg, CC, /*DiscardedValue*/ false).get());
   }
   FullExprArg MakeFullDiscardedValueExpr(Expr *Arg) {
     ExprResult FE =
         ActOnFinishFullExpr(Arg, Arg ? Arg->getExprLoc() : SourceLocation(),
                             /*DiscardedValue*/ true);
     return FullExprArg(FE.get());
   }
 
   class ConditionResult {
     Decl *ConditionVar;
     FullExprArg Condition;
     bool Invalid;
     std::optional<bool> KnownValue;
 
     friend class Sema;
     ConditionResult(Sema &S, Decl *ConditionVar, FullExprArg Condition,
                     bool IsConstexpr)
         : ConditionVar(ConditionVar), Condition(Condition), Invalid(false) {
       if (IsConstexpr && Condition.get()) {
         if (std::optional<llvm::APSInt> Val =
                 Condition.get()->getIntegerConstantExpr(S.Context)) {
           KnownValue = !!(*Val);
         }
       }
     }
     explicit ConditionResult(bool Invalid)
         : ConditionVar(nullptr), Condition(nullptr), Invalid(Invalid),
           KnownValue(std::nullopt) {}
 
   public:
     ConditionResult() : ConditionResult(false) {}
     bool isInvalid() const { return Invalid; }
     std::pair<VarDecl *, Expr *> get() const {
       return std::make_pair(cast_or_null<VarDecl>(ConditionVar),
                             Condition.get());
     }
     std::optional<bool> getKnownValue() const { return KnownValue; }
   };
   static ConditionResult ConditionError() { return ConditionResult(true); }
 
   /// CheckBooleanCondition - Diagnose problems involving the use of
   /// the given expression as a boolean condition (e.g. in an if
   /// statement).  Also performs the standard function and array
   /// decays, possibly changing the input variable.
   ///
   /// \param Loc - A location associated with the condition, e.g. the
   /// 'if' keyword.
   /// \return true iff there were any errors
   ExprResult CheckBooleanCondition(SourceLocation Loc, Expr *E,
                                    bool IsConstexpr = false);
 
   enum class ConditionKind {
     Boolean,     ///< A boolean condition, from 'if', 'while', 'for', or 'do'.
     ConstexprIf, ///< A constant boolean condition from 'if constexpr'.
     Switch       ///< An integral condition for a 'switch' statement.
   };
 
   ConditionResult ActOnCondition(Scope *S, SourceLocation Loc, Expr *SubExpr,
                                  ConditionKind CK, bool MissingOK = false);
 
   QualType CheckConditionalOperands( // C99 6.5.15
       ExprResult &Cond, ExprResult &LHS, ExprResult &RHS, ExprValueKind &VK,
       ExprObjectKind &OK, SourceLocation QuestionLoc);
 
   /// Emit a specialized diagnostic when one expression is a null pointer
   /// constant and the other is not a pointer.  Returns true if a diagnostic is
   /// emitted.
   bool DiagnoseConditionalForNull(const Expr *LHSExpr, const Expr *RHSExpr,
                                   SourceLocation QuestionLoc);
 
   /// type checking for vector binary operators.
   QualType CheckVectorOperands(ExprResult &LHS, ExprResult &RHS,
                                SourceLocation Loc, bool IsCompAssign,
                                bool AllowBothBool, bool AllowBoolConversion,
                                bool AllowBoolOperation, bool ReportInvalid);
 
   /// Return a signed ext_vector_type that is of identical size and number of
   /// elements. For floating point vectors, return an integer type of identical
   /// size and number of elements. In the non ext_vector_type case, search from
   /// the largest type to the smallest type to avoid cases where long long ==
   /// long, where long gets picked over long long.
   QualType GetSignedVectorType(QualType V);
   QualType GetSignedSizelessVectorType(QualType V);
 
   /// CheckVectorCompareOperands - vector comparisons are a clang extension that
   /// operates on extended vector types.  Instead of producing an IntTy result,
   /// like a scalar comparison, a vector comparison produces a vector of integer
   /// types.
   QualType CheckVectorCompareOperands(ExprResult &LHS, ExprResult &RHS,
                                       SourceLocation Loc,
                                       BinaryOperatorKind Opc);
   QualType CheckSizelessVectorCompareOperands(ExprResult &LHS, ExprResult &RHS,
                                               SourceLocation Loc,
                                               BinaryOperatorKind Opc);
   QualType CheckVectorLogicalOperands(ExprResult &LHS, ExprResult &RHS,
                                       SourceLocation Loc,
                                       BinaryOperatorKind Opc);
 
   /// Context in which we're performing a usual arithmetic conversion.
   enum ArithConvKind {
     /// An arithmetic operation.
     ACK_Arithmetic,
     /// A bitwise operation.
     ACK_BitwiseOp,
     /// A comparison.
     ACK_Comparison,
     /// A conditional (?:) operator.
     ACK_Conditional,
     /// A compound assignment expression.
     ACK_CompAssign,
   };
 
   // type checking for sizeless vector binary operators.
   QualType CheckSizelessVectorOperands(ExprResult &LHS, ExprResult &RHS,
                                        SourceLocation Loc, bool IsCompAssign,
                                        ArithConvKind OperationKind);
 
   /// Type checking for matrix binary operators.
   QualType CheckMatrixElementwiseOperands(ExprResult &LHS, ExprResult &RHS,
                                           SourceLocation Loc,
                                           bool IsCompAssign);
   QualType CheckMatrixMultiplyOperands(ExprResult &LHS, ExprResult &RHS,
                                        SourceLocation Loc, bool IsCompAssign);
 
   /// Are the two types SVE-bitcast-compatible types? I.e. is bitcasting from
   /// the first SVE type (e.g. an SVE VLAT) to the second type (e.g. an SVE
   /// VLST) allowed?
   ///
   /// This will also return false if the two given types do not make sense from
   /// the perspective of SVE bitcasts.
   bool isValidSveBitcast(QualType srcType, QualType destType);
 
   /// Are the two types matrix types and do they have the same dimensions i.e.
   /// do they have the same number of rows and the same number of columns?
   bool areMatrixTypesOfTheSameDimension(QualType srcTy, QualType destTy);
 
   bool areVectorTypesSameSize(QualType srcType, QualType destType);
 
   /// Are the two types lax-compatible vector types?  That is, given
   /// that one of them is a vector, do they have equal storage sizes,
   /// where the storage size is the number of elements times the element
   /// size?
   ///
   /// This will also return false if either of the types is neither a
   /// vector nor a real type.
   bool areLaxCompatibleVectorTypes(QualType srcType, QualType destType);
 
   /// Is this a legal conversion between two types, one of which is
   /// known to be a vector type?
   bool isLaxVectorConversion(QualType srcType, QualType destType);
 
   // This returns true if at least one of the types is an altivec vector.
   bool anyAltivecTypes(QualType srcType, QualType destType);
 
   // type checking C++ declaration initializers (C++ [dcl.init]).
 
   /// Check a cast of an unknown-any type.  We intentionally only
   /// trigger this for C-style casts.
   ExprResult checkUnknownAnyCast(SourceRange TypeRange, QualType CastType,
                                  Expr *CastExpr, CastKind &CastKind,
                                  ExprValueKind &VK, CXXCastPath &Path);
 
   /// Force an expression with unknown-type to an expression of the
   /// given type.
   ExprResult forceUnknownAnyToType(Expr *E, QualType ToType);
 
   /// Type-check an expression that's being passed to an
   /// __unknown_anytype parameter.
   ExprResult checkUnknownAnyArg(SourceLocation callLoc, Expr *result,
                                 QualType &paramType);
 
   // CheckMatrixCast - Check type constraints for matrix casts.
   // We allow casting between matrixes of the same dimensions i.e. when they
   // have the same number of rows and column. Returns true if the cast is
   // invalid.
   bool CheckMatrixCast(SourceRange R, QualType DestTy, QualType SrcTy,
                        CastKind &Kind);
 
   // CheckVectorCast - check type constraints for vectors.
   // Since vectors are an extension, there are no C standard reference for this.
   // We allow casting between vectors and integer datatypes of the same size.
   // returns true if the cast is invalid
   bool CheckVectorCast(SourceRange R, QualType VectorTy, QualType Ty,
                        CastKind &Kind);
 
   /// Prepare `SplattedExpr` for a vector splat operation, adding
   /// implicit casts if necessary.
   ExprResult prepareVectorSplat(QualType VectorTy, Expr *SplattedExpr);
 
   // CheckExtVectorCast - check type constraints for extended vectors.
   // Since vectors are an extension, there are no C standard reference for this.
   // We allow casting between vectors and integer datatypes of the same size,
   // or vectors and the element type of that vector.
   // returns the cast expr
   ExprResult CheckExtVectorCast(SourceRange R, QualType DestTy, Expr *CastExpr,
                                 CastKind &Kind);
 
   QualType PreferredConditionType(ConditionKind K) const {
     return K == ConditionKind::Switch ? Context.IntTy : Context.BoolTy;
   }
 
   // UsualUnaryConversions - promotes integers (C99 6.3.1.1p2) and converts
   // functions and arrays to their respective pointers (C99 6.3.2.1).
   ExprResult UsualUnaryConversions(Expr *E);
 
   /// CallExprUnaryConversions - a special case of an unary conversion
   /// performed on a function designator of a call expression.
   ExprResult CallExprUnaryConversions(Expr *E);
 
   // DefaultFunctionArrayConversion - converts functions and arrays
   // to their respective pointers (C99 6.3.2.1).
   ExprResult DefaultFunctionArrayConversion(Expr *E, bool Diagnose = true);
 
   // DefaultFunctionArrayLvalueConversion - converts functions and
   // arrays to their respective pointers and performs the
   // lvalue-to-rvalue conversion.
   ExprResult DefaultFunctionArrayLvalueConversion(Expr *E,
                                                   bool Diagnose = true);
 
   // DefaultLvalueConversion - performs lvalue-to-rvalue conversion on
   // the operand. This function is a no-op if the operand has a function type
   // or an array type.
   ExprResult DefaultLvalueConversion(Expr *E);
 
   // DefaultArgumentPromotion (C99 6.5.2.2p6). Used for function calls that
   // do not have a prototype. Integer promotions are performed on each
   // argument, and arguments that have type float are promoted to double.
   ExprResult DefaultArgumentPromotion(Expr *E);
 
   VariadicCallType getVariadicCallType(FunctionDecl *FDecl,
                                        const FunctionProtoType *Proto,
                                        Expr *Fn);
 
   // Used for determining in which context a type is allowed to be passed to a
   // vararg function.
   enum VarArgKind {
     VAK_Valid,
     VAK_ValidInCXX11,
     VAK_Undefined,
     VAK_MSVCUndefined,
     VAK_Invalid
   };
 
   /// Determine the degree of POD-ness for an expression.
   /// Incomplete types are considered POD, since this check can be performed
   /// when we're in an unevaluated context.
   VarArgKind isValidVarArgType(const QualType &Ty);
 
   /// Check to see if the given expression is a valid argument to a variadic
   /// function, issuing a diagnostic if not.
   void checkVariadicArgument(const Expr *E, VariadicCallType CT);
 
   /// GatherArgumentsForCall - Collector argument expressions for various
   /// form of call prototypes.
   bool GatherArgumentsForCall(SourceLocation CallLoc, FunctionDecl *FDecl,
                               const FunctionProtoType *Proto,
                               unsigned FirstParam, ArrayRef<Expr *> Args,
                               SmallVectorImpl<Expr *> &AllArgs,
                               VariadicCallType CallType = VariadicDoesNotApply,
                               bool AllowExplicit = false,
                               bool IsListInitialization = false);
 
   // DefaultVariadicArgumentPromotion - Like DefaultArgumentPromotion, but
   // will create a runtime trap if the resulting type is not a POD type.
   ExprResult DefaultVariadicArgumentPromotion(Expr *E, VariadicCallType CT,
                                               FunctionDecl *FDecl);
 
   // UsualArithmeticConversions - performs the UsualUnaryConversions on it's
   // operands and then handles various conversions that are common to binary
   // operators (C99 6.3.1.8). If both operands aren't arithmetic, this
   // routine returns the first non-arithmetic type found. The client is
   // responsible for emitting appropriate error diagnostics.
   QualType UsualArithmeticConversions(ExprResult &LHS, ExprResult &RHS,
                                       SourceLocation Loc, ArithConvKind ACK);
 
   /// AssignConvertType - All of the 'assignment' semantic checks return this
   /// enum to indicate whether the assignment was allowed.  These checks are
   /// done for simple assignments, as well as initialization, return from
   /// function, argument passing, etc.  The query is phrased in terms of a
   /// source and destination type.
   enum AssignConvertType {
     /// Compatible - the types are compatible according to the standard.
     Compatible,
 
     /// PointerToInt - The assignment converts a pointer to an int, which we
     /// accept as an extension.
     PointerToInt,
 
     /// IntToPointer - The assignment converts an int to a pointer, which we
     /// accept as an extension.
     IntToPointer,
 
     /// FunctionVoidPointer - The assignment is between a function pointer and
     /// void*, which the standard doesn't allow, but we accept as an extension.
     FunctionVoidPointer,
 
     /// IncompatiblePointer - The assignment is between two pointers types that
     /// are not compatible, but we accept them as an extension.
     IncompatiblePointer,
 
     /// IncompatibleFunctionPointer - The assignment is between two function
     /// pointers types that are not compatible, but we accept them as an
     /// extension.
     IncompatibleFunctionPointer,
 
     /// IncompatibleFunctionPointerStrict - The assignment is between two
     /// function pointer types that are not identical, but are compatible,
     /// unless compiled with -fsanitize=cfi, in which case the type mismatch
     /// may trip an indirect call runtime check.
     IncompatibleFunctionPointerStrict,
 
     /// IncompatiblePointerSign - The assignment is between two pointers types
     /// which point to integers which have a different sign, but are otherwise
     /// identical. This is a subset of the above, but broken out because it's by
     /// far the most common case of incompatible pointers.
     IncompatiblePointerSign,
 
     /// CompatiblePointerDiscardsQualifiers - The assignment discards
     /// c/v/r qualifiers, which we accept as an extension.
     CompatiblePointerDiscardsQualifiers,
 
     /// IncompatiblePointerDiscardsQualifiers - The assignment
     /// discards qualifiers that we don't permit to be discarded,
     /// like address spaces.
     IncompatiblePointerDiscardsQualifiers,
 
     /// IncompatibleNestedPointerAddressSpaceMismatch - The assignment
     /// changes address spaces in nested pointer types which is not allowed.
     /// For instance, converting __private int ** to __generic int ** is
     /// illegal even though __private could be converted to __generic.
     IncompatibleNestedPointerAddressSpaceMismatch,
 
     /// IncompatibleNestedPointerQualifiers - The assignment is between two
     /// nested pointer types, and the qualifiers other than the first two
     /// levels differ e.g. char ** -> const char **, but we accept them as an
     /// extension.
     IncompatibleNestedPointerQualifiers,
 
     /// IncompatibleVectors - The assignment is between two vector types that
     /// have the same size, which we accept as an extension.
     IncompatibleVectors,
 
     /// IntToBlockPointer - The assignment converts an int to a block
     /// pointer. We disallow this.
     IntToBlockPointer,
 
     /// IncompatibleBlockPointer - The assignment is between two block
     /// pointers types that are not compatible.
     IncompatibleBlockPointer,
 
     /// IncompatibleObjCQualifiedId - The assignment is between a qualified
     /// id type and something else (that is incompatible with it). For example,
     /// "id <XXX>" = "Foo *", where "Foo *" doesn't implement the XXX protocol.
     IncompatibleObjCQualifiedId,
 
     /// IncompatibleObjCWeakRef - Assigning a weak-unavailable object to an
     /// object with __weak qualifier.
     IncompatibleObjCWeakRef,
 
     /// Incompatible - We reject this conversion outright, it is invalid to
     /// represent it in the AST.
     Incompatible
   };
 
   /// DiagnoseAssignmentResult - Emit a diagnostic, if required, for the
   /// assignment conversion type specified by ConvTy.  This returns true if the
   /// conversion was invalid or false if the conversion was accepted.
   bool DiagnoseAssignmentResult(AssignConvertType ConvTy, SourceLocation Loc,
                                 QualType DstType, QualType SrcType,
                                 Expr *SrcExpr, AssignmentAction Action,
                                 bool *Complained = nullptr);
 
   /// CheckAssignmentConstraints - Perform type checking for assignment,
   /// argument passing, variable initialization, and function return values.
   /// C99 6.5.16.
   AssignConvertType CheckAssignmentConstraints(SourceLocation Loc,
                                                QualType LHSType,
                                                QualType RHSType);
 
   /// Check assignment constraints and optionally prepare for a conversion of
   /// the RHS to the LHS type. The conversion is prepared for if ConvertRHS
   /// is true.
   AssignConvertType CheckAssignmentConstraints(QualType LHSType,
                                                ExprResult &RHS, CastKind &Kind,
                                                bool ConvertRHS = true);
 
   /// Check assignment constraints for an assignment of RHS to LHSType.
   ///
   /// \param LHSType The destination type for the assignment.
   /// \param RHS The source expression for the assignment.
   /// \param Diagnose If \c true, diagnostics may be produced when checking
   ///        for assignability. If a diagnostic is produced, \p RHS will be
   ///        set to ExprError(). Note that this function may still return
   ///        without producing a diagnostic, even for an invalid assignment.
   /// \param DiagnoseCFAudited If \c true, the target is a function parameter
   ///        in an audited Core Foundation API and does not need to be checked
   ///        for ARC retain issues.
   /// \param ConvertRHS If \c true, \p RHS will be updated to model the
   ///        conversions necessary to perform the assignment. If \c false,
   ///        \p Diagnose must also be \c false.
   AssignConvertType CheckSingleAssignmentConstraints(
       QualType LHSType, ExprResult &RHS, bool Diagnose = true,
       bool DiagnoseCFAudited = false, bool ConvertRHS = true);
 
   // If the lhs type is a transparent union, check whether we
   // can initialize the transparent union with the given expression.
   AssignConvertType CheckTransparentUnionArgumentConstraints(QualType ArgType,
                                                              ExprResult &RHS);
 
   /// the following "Check" methods will return a valid/converted QualType
   /// or a null QualType (indicating an error diagnostic was issued).
 
   /// type checking binary operators (subroutines of CreateBuiltinBinOp).
   QualType InvalidOperands(SourceLocation Loc, ExprResult &LHS,
                            ExprResult &RHS);
 
   /// Diagnose cases where a scalar was implicitly converted to a vector and
   /// diagnose the underlying types. Otherwise, diagnose the error
   /// as invalid vector logical operands for non-C++ cases.
   QualType InvalidLogicalVectorOperands(SourceLocation Loc, ExprResult &LHS,
                                         ExprResult &RHS);
 
   QualType CheckMultiplyDivideOperands( // C99 6.5.5
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc, bool IsCompAssign,
       bool IsDivide);
   QualType CheckRemainderOperands( // C99 6.5.5
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       bool IsCompAssign = false);
   QualType CheckAdditionOperands( // C99 6.5.6
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc, QualType *CompLHSTy = nullptr);
   QualType CheckSubtractionOperands( // C99 6.5.6
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       QualType *CompLHSTy = nullptr);
   QualType CheckShiftOperands( // C99 6.5.7
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc, bool IsCompAssign = false);
   void CheckPtrComparisonWithNullChar(ExprResult &E, ExprResult &NullE);
   QualType CheckCompareOperands( // C99 6.5.8/9
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc);
   QualType CheckBitwiseOperands( // C99 6.5.[10...12]
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc);
   QualType CheckLogicalOperands( // C99 6.5.[13,14]
       ExprResult &LHS, ExprResult &RHS, SourceLocation Loc,
       BinaryOperatorKind Opc);
   // CheckAssignmentOperands is used for both simple and compound assignment.
   // For simple assignment, pass both expressions and a null converted type.
   // For compound assignment, pass both expressions and the converted type.
   QualType CheckAssignmentOperands( // C99 6.5.16.[1,2]
       Expr *LHSExpr, ExprResult &RHS, SourceLocation Loc, QualType CompoundType,
       BinaryOperatorKind Opc);
 
   /// To be used for checking whether the arguments being passed to
   /// function exceeds the number of parameters expected for it.
   static bool TooManyArguments(size_t NumParams, size_t NumArgs,
                                bool PartialOverloading = false) {
     // We check whether we're just after a comma in code-completion.
     if (NumArgs > 0 && PartialOverloading)
       return NumArgs + 1 > NumParams; // If so, we view as an extra argument.
     return NumArgs > NumParams;
   }
 
   /// Whether the AST is currently being rebuilt to correct immediate
   /// invocations. Immediate invocation candidates and references to consteval
   /// functions aren't tracked when this is set.
   bool RebuildingImmediateInvocation = false;
 
   bool isAlwaysConstantEvaluatedContext() const {
     const ExpressionEvaluationContextRecord &Ctx = currentEvaluationContext();
     return (Ctx.isConstantEvaluated() || isConstantEvaluatedOverride) &&
            !Ctx.InConditionallyConstantEvaluateContext;
   }
 
   /// Determines whether we are currently in a context that
   /// is not evaluated as per C++ [expr] p5.
   bool isUnevaluatedContext() const {
     return currentEvaluationContext().isUnevaluated();
   }
 
   bool isImmediateFunctionContext() const {
     return currentEvaluationContext().isImmediateFunctionContext();
   }
 
   bool isInLifetimeExtendingContext() const {
     return currentEvaluationContext().InLifetimeExtendingContext;
   }
 
   bool needsRebuildOfDefaultArgOrInit() const {
     return currentEvaluationContext().RebuildDefaultArgOrDefaultInit;
   }
 
   bool isCheckingDefaultArgumentOrInitializer() const {
     const ExpressionEvaluationContextRecord &Ctx = currentEvaluationContext();
     return (Ctx.Context ==
             ExpressionEvaluationContext::PotentiallyEvaluatedIfUsed) ||
            Ctx.IsCurrentlyCheckingDefaultArgumentOrInitializer;
   }
 
   std::optional<ExpressionEvaluationContextRecord::InitializationContext>
   InnermostDeclarationWithDelayedImmediateInvocations() const {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
     for (const auto &Ctx : llvm::reverse(ExprEvalContexts)) {
       if (Ctx.Context == ExpressionEvaluationContext::PotentiallyEvaluated &&
           Ctx.DelayedDefaultInitializationContext)
         return Ctx.DelayedDefaultInitializationContext;
       if (Ctx.isConstantEvaluated() || Ctx.isImmediateFunctionContext() ||
           Ctx.isUnevaluated())
         break;
     }
     return std::nullopt;
   }
 
   std::optional<ExpressionEvaluationContextRecord::InitializationContext>
   OutermostDeclarationWithDelayedImmediateInvocations() const {
     assert(!ExprEvalContexts.empty() &&
            "Must be in an expression evaluation context");
     std::optional<ExpressionEvaluationContextRecord::InitializationContext> Res;
     for (auto &Ctx : llvm::reverse(ExprEvalContexts)) {
       if (Ctx.Context == ExpressionEvaluationContext::PotentiallyEvaluated &&
           !Ctx.DelayedDefaultInitializationContext && Res)
         break;
       if (Ctx.isConstantEvaluated() || Ctx.isImmediateFunctionContext() ||
           Ctx.isUnevaluated())
         break;
       Res = Ctx.DelayedDefaultInitializationContext;
     }
     return Res;
   }
 
   DefaultedComparisonKind getDefaultedComparisonKind(const FunctionDecl *FD) {
     return getDefaultedFunctionKind(FD).asComparison();
   }
 
   /// Returns a field in a CXXRecordDecl that has the same name as the decl \p
   /// SelfAssigned when inside a CXXMethodDecl.
   const FieldDecl *
   getSelfAssignmentClassMemberCandidate(const ValueDecl *SelfAssigned);
 
   void MaybeSuggestAddingStaticToDecl(const FunctionDecl *D);
 
   template <typename... Ts>
   bool RequireCompleteSizedType(SourceLocation Loc, QualType T, unsigned DiagID,
                                 const Ts &...Args) {
     SizelessTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireCompleteType(Loc, T, CompleteTypeKind::Normal, Diagnoser);
   }
 
   template <typename... Ts>
   bool RequireCompleteSizedExprType(Expr *E, unsigned DiagID,
                                     const Ts &...Args) {
     SizelessTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireCompleteExprType(E, CompleteTypeKind::Normal, Diagnoser);
   }
 
   /// Abstract class used to diagnose incomplete types.
   struct TypeDiagnoser {
     TypeDiagnoser() {}
 
     virtual void diagnose(Sema &S, SourceLocation Loc, QualType T) = 0;
     virtual ~TypeDiagnoser() {}
   };
 
   template <typename... Ts> class BoundTypeDiagnoser : public TypeDiagnoser {
   protected:
     unsigned DiagID;
     std::tuple<const Ts &...> Args;
 
     template <std::size_t... Is>
     void emit(const SemaDiagnosticBuilder &DB,
               std::index_sequence<Is...>) const {
       // Apply all tuple elements to the builder in order.
       bool Dummy[] = {false, (DB << getPrintable(std::get<Is>(Args)))...};
       (void)Dummy;
     }
 
   public:
     BoundTypeDiagnoser(unsigned DiagID, const Ts &...Args)
         : TypeDiagnoser(), DiagID(DiagID), Args(Args...) {
       assert(DiagID != 0 && "no diagnostic for type diagnoser");
     }
 
     void diagnose(Sema &S, SourceLocation Loc, QualType T) override {
       const SemaDiagnosticBuilder &DB = S.Diag(Loc, DiagID);
       emit(DB, std::index_sequence_for<Ts...>());
       DB << T;
     }
   };
 
   /// A derivative of BoundTypeDiagnoser for which the diagnostic's type
   /// parameter is preceded by a 0/1 enum that is 1 if the type is sizeless.
   /// For example, a diagnostic with no other parameters would generally have
   /// the form "...%select{incomplete|sizeless}0 type %1...".
   template <typename... Ts>
   class SizelessTypeDiagnoser : public BoundTypeDiagnoser<Ts...> {
   public:
     SizelessTypeDiagnoser(unsigned DiagID, const Ts &...Args)
         : BoundTypeDiagnoser<Ts...>(DiagID, Args...) {}
 
     void diagnose(Sema &S, SourceLocation Loc, QualType T) override {
       const SemaDiagnosticBuilder &DB = S.Diag(Loc, this->DiagID);
       this->emit(DB, std::index_sequence_for<Ts...>());
       DB << T->isSizelessType() << T;
     }
   };
 
   /// Check an argument list for placeholders that we won't try to
   /// handle later.
   bool CheckArgsForPlaceholders(MultiExprArg args);
 
   /// The C++ "std::source_location::__impl" struct, defined in
   /// \<source_location>.
   RecordDecl *StdSourceLocationImplDecl;
 
   /// A stack of expression evaluation contexts.
   SmallVector<ExpressionEvaluationContextRecord, 8> ExprEvalContexts;
 
   // Set of failed immediate invocations to avoid double diagnosing.
   llvm::SmallPtrSet<ConstantExpr *, 4> FailedImmediateInvocations;
 
   /// List of SourceLocations where 'self' is implicitly retained inside a
   /// block.
   llvm::SmallVector<std::pair<SourceLocation, const BlockDecl *>, 1>
       ImplicitlyRetainedSelfLocs;
 
   /// Do an explicit extend of the given block pointer if we're in ARC.
   void maybeExtendBlockObject(ExprResult &E);
 
   std::vector<std::pair<QualType, unsigned>> ExcessPrecisionNotSatisfied;
   SourceLocation LocationOfExcessPrecisionNotSatisfied;
   void DiagnosePrecisionLossInComplexDivision();
 
 private:
   static BinaryOperatorKind ConvertTokenKindToBinaryOpcode(tok::TokenKind Kind);
 
   /// Methods for marking which expressions involve dereferencing a pointer
   /// marked with the 'noderef' attribute. Expressions are checked bottom up as
   /// they are parsed, meaning that a noderef pointer may not be accessed. For
   /// example, in `&*p` where `p` is a noderef pointer, we will first parse the
   /// `*p`, but need to check that `address of` is called on it. This requires
   /// keeping a container of all pending expressions and checking if the address
   /// of them are eventually taken.
   void CheckSubscriptAccessOfNoDeref(const ArraySubscriptExpr *E);
   void CheckAddressOfNoDeref(const Expr *E);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Expressions
   /// Implementations are in SemaExprCXX.cpp
   ///@{
 
 public:
   /// The C++ "std::bad_alloc" class, which is defined by the C++
   /// standard library.
   LazyDeclPtr StdBadAlloc;
 
   /// The C++ "std::align_val_t" enum class, which is defined by the C++
   /// standard library.
   LazyDeclPtr StdAlignValT;
 
   /// The C++ "type_info" declaration, which is defined in \<typeinfo>.
   RecordDecl *CXXTypeInfoDecl;
 
   /// A flag to remember whether the implicit forms of operator new and delete
   /// have been declared.
   bool GlobalNewDeleteDeclared;
 
   /// Delete-expressions to be analyzed at the end of translation unit
   ///
   /// This list contains class members, and locations of delete-expressions
   /// that could not be proven as to whether they mismatch with new-expression
   /// used in initializer of the field.
   llvm::MapVector<FieldDecl *, DeleteLocs> DeleteExprs;
 
   /// Handle the result of the special case name lookup for inheriting
   /// constructor declarations. 'NS::X::X' and 'NS::X<...>::X' are treated as
   /// constructor names in member using declarations, even if 'X' is not the
   /// name of the corresponding type.
   ParsedType getInheritingConstructorName(CXXScopeSpec &SS,
                                           SourceLocation NameLoc,
                                           const IdentifierInfo &Name);
 
   ParsedType getConstructorName(const IdentifierInfo &II,
                                 SourceLocation NameLoc, Scope *S,
                                 CXXScopeSpec &SS, bool EnteringContext);
   ParsedType getDestructorName(const IdentifierInfo &II, SourceLocation NameLoc,
                                Scope *S, CXXScopeSpec &SS,
                                ParsedType ObjectType, bool EnteringContext);
 
   ParsedType getDestructorTypeForDecltype(const DeclSpec &DS,
                                           ParsedType ObjectType);
 
   /// Build a C++ typeid expression with a type operand.
   ExprResult BuildCXXTypeId(QualType TypeInfoType, SourceLocation TypeidLoc,
                             TypeSourceInfo *Operand, SourceLocation RParenLoc);
 
   /// Build a C++ typeid expression with an expression operand.
   ExprResult BuildCXXTypeId(QualType TypeInfoType, SourceLocation TypeidLoc,
                             Expr *Operand, SourceLocation RParenLoc);
 
   /// ActOnCXXTypeid - Parse typeid( something ).
   ExprResult ActOnCXXTypeid(SourceLocation OpLoc, SourceLocation LParenLoc,
                             bool isType, void *TyOrExpr,
                             SourceLocation RParenLoc);
 
   /// Build a Microsoft __uuidof expression with a type operand.
   ExprResult BuildCXXUuidof(QualType TypeInfoType, SourceLocation TypeidLoc,
                             TypeSourceInfo *Operand, SourceLocation RParenLoc);
 
   /// Build a Microsoft __uuidof expression with an expression operand.
   ExprResult BuildCXXUuidof(QualType TypeInfoType, SourceLocation TypeidLoc,
                             Expr *Operand, SourceLocation RParenLoc);
 
   /// ActOnCXXUuidof - Parse __uuidof( something ).
   ExprResult ActOnCXXUuidof(SourceLocation OpLoc, SourceLocation LParenLoc,
                             bool isType, void *TyOrExpr,
                             SourceLocation RParenLoc);
 
   //// ActOnCXXThis -  Parse 'this' pointer.
   ExprResult ActOnCXXThis(SourceLocation Loc);
 
   /// Check whether the type of 'this' is valid in the current context.
   bool CheckCXXThisType(SourceLocation Loc, QualType Type);
 
   /// Build a CXXThisExpr and mark it referenced in the current context.
   Expr *BuildCXXThisExpr(SourceLocation Loc, QualType Type, bool IsImplicit);
   void MarkThisReferenced(CXXThisExpr *This);
 
   /// Try to retrieve the type of the 'this' pointer.
   ///
   /// \returns The type of 'this', if possible. Otherwise, returns a NULL type.
   QualType getCurrentThisType();
 
   /// When non-NULL, the C++ 'this' expression is allowed despite the
   /// current context not being a non-static member function. In such cases,
   /// this provides the type used for 'this'.
   QualType CXXThisTypeOverride;
 
   /// RAII object used to temporarily allow the C++ 'this' expression
   /// to be used, with the given qualifiers on the current class type.
   class CXXThisScopeRAII {
     Sema &S;
     QualType OldCXXThisTypeOverride;
     bool Enabled;
 
   public:
     /// Introduce a new scope where 'this' may be allowed (when enabled),
     /// using the given declaration (which is either a class template or a
     /// class) along with the given qualifiers.
     /// along with the qualifiers placed on '*this'.
     CXXThisScopeRAII(Sema &S, Decl *ContextDecl, Qualifiers CXXThisTypeQuals,
                      bool Enabled = true);
 
     ~CXXThisScopeRAII();
   };
 
   /// Make sure the value of 'this' is actually available in the current
   /// context, if it is a potentially evaluated context.
   ///
   /// \param Loc The location at which the capture of 'this' occurs.
   ///
   /// \param Explicit Whether 'this' is explicitly captured in a lambda
   /// capture list.
   ///
   /// \param FunctionScopeIndexToStopAt If non-null, it points to the index
   /// of the FunctionScopeInfo stack beyond which we do not attempt to capture.
   /// This is useful when enclosing lambdas must speculatively capture
   /// 'this' that may or may not be used in certain specializations of
   /// a nested generic lambda (depending on whether the name resolves to
   /// a non-static member function or a static function).
   /// \return returns 'true' if failed, 'false' if success.
   bool CheckCXXThisCapture(
       SourceLocation Loc, bool Explicit = false, bool BuildAndDiagnose = true,
       const unsigned *const FunctionScopeIndexToStopAt = nullptr,
       bool ByCopy = false);
 
   /// Determine whether the given type is the type of *this that is used
   /// outside of the body of a member function for a type that is currently
   /// being defined.
   bool isThisOutsideMemberFunctionBody(QualType BaseType);
 
   /// ActOnCXXBoolLiteral - Parse {true,false} literals.
   ExprResult ActOnCXXBoolLiteral(SourceLocation OpLoc, tok::TokenKind Kind);
 
   /// ActOnCXXNullPtrLiteral - Parse 'nullptr'.
   ExprResult ActOnCXXNullPtrLiteral(SourceLocation Loc);
 
   //// ActOnCXXThrow -  Parse throw expressions.
   ExprResult ActOnCXXThrow(Scope *S, SourceLocation OpLoc, Expr *expr);
   ExprResult BuildCXXThrow(SourceLocation OpLoc, Expr *Ex,
                            bool IsThrownVarInScope);
 
   /// CheckCXXThrowOperand - Validate the operand of a throw.
   bool CheckCXXThrowOperand(SourceLocation ThrowLoc, QualType ThrowTy, Expr *E);
 
   /// ActOnCXXTypeConstructExpr - Parse construction of a specified type.
   /// Can be interpreted either as function-style casting ("int(x)")
   /// or class type construction ("ClassType(x,y,z)")
   /// or creation of a value-initialized type ("int()").
   ExprResult ActOnCXXTypeConstructExpr(ParsedType TypeRep,
                                        SourceLocation LParenOrBraceLoc,
                                        MultiExprArg Exprs,
                                        SourceLocation RParenOrBraceLoc,
                                        bool ListInitialization);
 
   ExprResult BuildCXXTypeConstructExpr(TypeSourceInfo *Type,
                                        SourceLocation LParenLoc,
                                        MultiExprArg Exprs,
                                        SourceLocation RParenLoc,
                                        bool ListInitialization);
 
   /// Parsed a C++ 'new' expression (C++ 5.3.4).
   ///
   /// E.g.:
   /// @code new (memory) int[size][4] @endcode
   /// or
   /// @code ::new Foo(23, "hello") @endcode
   ///
   /// \param StartLoc The first location of the expression.
   /// \param UseGlobal True if 'new' was prefixed with '::'.
   /// \param PlacementLParen Opening paren of the placement arguments.
   /// \param PlacementArgs Placement new arguments.
   /// \param PlacementRParen Closing paren of the placement arguments.
   /// \param TypeIdParens If the type is in parens, the source range.
   /// \param D The type to be allocated, as well as array dimensions.
   /// \param Initializer The initializing expression or initializer-list, or
   ///   null if there is none.
   ExprResult ActOnCXXNew(SourceLocation StartLoc, bool UseGlobal,
                          SourceLocation PlacementLParen,
                          MultiExprArg PlacementArgs,
                          SourceLocation PlacementRParen,
                          SourceRange TypeIdParens, Declarator &D,
                          Expr *Initializer);
   ExprResult
   BuildCXXNew(SourceRange Range, bool UseGlobal, SourceLocation PlacementLParen,
               MultiExprArg PlacementArgs, SourceLocation PlacementRParen,
               SourceRange TypeIdParens, QualType AllocType,
               TypeSourceInfo *AllocTypeInfo, std::optional<Expr *> ArraySize,
               SourceRange DirectInitRange, Expr *Initializer);
 
   /// Determine whether \p FD is an aligned allocation or deallocation
   /// function that is unavailable.
   bool isUnavailableAlignedAllocationFunction(const FunctionDecl &FD) const;
 
   /// Produce diagnostics if \p FD is an aligned allocation or deallocation
   /// function that is unavailable.
   void diagnoseUnavailableAlignedAllocation(const FunctionDecl &FD,
                                             SourceLocation Loc);
 
   /// Checks that a type is suitable as the allocated type
   /// in a new-expression.
   bool CheckAllocatedType(QualType AllocType, SourceLocation Loc,
                           SourceRange R);
 
   /// The scope in which to find allocation functions.
   enum AllocationFunctionScope {
     /// Only look for allocation functions in the global scope.
     AFS_Global,
     /// Only look for allocation functions in the scope of the
     /// allocated class.
     AFS_Class,
     /// Look for allocation functions in both the global scope
     /// and in the scope of the allocated class.
     AFS_Both
   };
 
   /// Finds the overloads of operator new and delete that are appropriate
   /// for the allocation.
   bool FindAllocationFunctions(SourceLocation StartLoc, SourceRange Range,
                                AllocationFunctionScope NewScope,
                                AllocationFunctionScope DeleteScope,
                                QualType AllocType, bool IsArray,
                                bool &PassAlignment, MultiExprArg PlaceArgs,
                                FunctionDecl *&OperatorNew,
                                FunctionDecl *&OperatorDelete,
                                bool Diagnose = true);
 
   /// DeclareGlobalNewDelete - Declare the global forms of operator new and
   /// delete. These are:
   /// @code
   ///   // C++03:
   ///   void* operator new(std::size_t) throw(std::bad_alloc);
   ///   void* operator new[](std::size_t) throw(std::bad_alloc);
   ///   void operator delete(void *) throw();
   ///   void operator delete[](void *) throw();
   ///   // C++11:
   ///   void* operator new(std::size_t);
   ///   void* operator new[](std::size_t);
   ///   void operator delete(void *) noexcept;
   ///   void operator delete[](void *) noexcept;
   ///   // C++1y:
   ///   void* operator new(std::size_t);
   ///   void* operator new[](std::size_t);
   ///   void operator delete(void *) noexcept;
   ///   void operator delete[](void *) noexcept;
   ///   void operator delete(void *, std::size_t) noexcept;
   ///   void operator delete[](void *, std::size_t) noexcept;
   /// @endcode
   /// Note that the placement and nothrow forms of new are *not* implicitly
   /// declared. Their use requires including \<new\>.
   void DeclareGlobalNewDelete();
   void DeclareGlobalAllocationFunction(DeclarationName Name, QualType Return,
                                        ArrayRef<QualType> Params);
 
   bool FindDeallocationFunction(SourceLocation StartLoc, CXXRecordDecl *RD,
                                 DeclarationName Name, FunctionDecl *&Operator,
                                 bool Diagnose = true, bool WantSize = false,
                                 bool WantAligned = false);
   FunctionDecl *FindUsualDeallocationFunction(SourceLocation StartLoc,
                                               bool CanProvideSize,
                                               bool Overaligned,
                                               DeclarationName Name);
   FunctionDecl *FindDeallocationFunctionForDestructor(SourceLocation StartLoc,
                                                       CXXRecordDecl *RD);
 
   /// ActOnCXXDelete - Parsed a C++ 'delete' expression (C++ 5.3.5), as in:
   /// @code ::delete ptr; @endcode
   /// or
   /// @code delete [] ptr; @endcode
   ExprResult ActOnCXXDelete(SourceLocation StartLoc, bool UseGlobal,
                             bool ArrayForm, Expr *Operand);
   void CheckVirtualDtorCall(CXXDestructorDecl *dtor, SourceLocation Loc,
                             bool IsDelete, bool CallCanBeVirtual,
                             bool WarnOnNonAbstractTypes,
                             SourceLocation DtorLoc);
 
   ExprResult ActOnNoexceptExpr(SourceLocation KeyLoc, SourceLocation LParen,
                                Expr *Operand, SourceLocation RParen);
   ExprResult BuildCXXNoexceptExpr(SourceLocation KeyLoc, Expr *Operand,
                                   SourceLocation RParen);
 
   ExprResult ActOnStartCXXMemberReference(Scope *S, Expr *Base,
                                           SourceLocation OpLoc,
                                           tok::TokenKind OpKind,
                                           ParsedType &ObjectType,
                                           bool &MayBePseudoDestructor);
 
   ExprResult BuildPseudoDestructorExpr(
       Expr *Base, SourceLocation OpLoc, tok::TokenKind OpKind,
       const CXXScopeSpec &SS, TypeSourceInfo *ScopeType, SourceLocation CCLoc,
       SourceLocation TildeLoc, PseudoDestructorTypeStorage DestroyedType);
 
   ExprResult ActOnPseudoDestructorExpr(
       Scope *S, Expr *Base, SourceLocation OpLoc, tok::TokenKind OpKind,
       CXXScopeSpec &SS, UnqualifiedId &FirstTypeName, SourceLocation CCLoc,
       SourceLocation TildeLoc, UnqualifiedId &SecondTypeName);
 
   ExprResult ActOnPseudoDestructorExpr(Scope *S, Expr *Base,
                                        SourceLocation OpLoc,
                                        tok::TokenKind OpKind,
                                        SourceLocation TildeLoc,
                                        const DeclSpec &DS);
 
   /// MaybeCreateExprWithCleanups - If the current full-expression
   /// requires any cleanups, surround it with a ExprWithCleanups node.
   /// Otherwise, just returns the passed-in expression.
   Expr *MaybeCreateExprWithCleanups(Expr *SubExpr);
   Stmt *MaybeCreateStmtWithCleanups(Stmt *SubStmt);
   ExprResult MaybeCreateExprWithCleanups(ExprResult SubExpr);
 
   ExprResult ActOnFinishFullExpr(Expr *Expr, bool DiscardedValue) {
     return ActOnFinishFullExpr(
         Expr, Expr ? Expr->getExprLoc() : SourceLocation(), DiscardedValue);
   }
   ExprResult ActOnFinishFullExpr(Expr *Expr, SourceLocation CC,
                                  bool DiscardedValue, bool IsConstexpr = false,
                                  bool IsTemplateArgument = false);
   StmtResult ActOnFinishFullStmt(Stmt *Stmt);
 
   /// Process the expression contained within a decltype. For such expressions,
   /// certain semantic checks on temporaries are delayed until this point, and
   /// are omitted for the 'topmost' call in the decltype expression. If the
   /// topmost call bound a temporary, strip that temporary off the expression.
   ExprResult ActOnDecltypeExpression(Expr *E);
 
   bool checkLiteralOperatorId(const CXXScopeSpec &SS, const UnqualifiedId &Id,
                               bool IsUDSuffix);
 
   bool isUsualDeallocationFunction(const CXXMethodDecl *FD);
 
   ConditionResult ActOnConditionVariable(Decl *ConditionVar,
                                          SourceLocation StmtLoc,
                                          ConditionKind CK);
 
   /// Check the use of the given variable as a C++ condition in an if,
   /// while, do-while, or switch statement.
   ExprResult CheckConditionVariable(VarDecl *ConditionVar,
                                     SourceLocation StmtLoc, ConditionKind CK);
 
   /// CheckCXXBooleanCondition - Returns true if conversion to bool is invalid.
   ExprResult CheckCXXBooleanCondition(Expr *CondExpr, bool IsConstexpr = false);
 
   /// Helper function to determine whether this is the (deprecated) C++
   /// conversion from a string literal to a pointer to non-const char or
   /// non-const wchar_t (for narrow and wide string literals,
   /// respectively).
   bool IsStringLiteralToNonConstPointerConversion(Expr *From, QualType ToType);
 
   /// PerformImplicitConversion - Perform an implicit conversion of the
   /// expression From to the type ToType using the pre-computed implicit
   /// conversion sequence ICS. Returns the converted
   /// expression. Action is the kind of conversion we're performing,
   /// used in the error message.
   ExprResult PerformImplicitConversion(
       Expr *From, QualType ToType, const ImplicitConversionSequence &ICS,
       AssignmentAction Action,
       CheckedConversionKind CCK = CheckedConversionKind::Implicit);
 
   /// PerformImplicitConversion - Perform an implicit conversion of the
   /// expression From to the type ToType by following the standard
   /// conversion sequence SCS. Returns the converted
   /// expression. Flavor is the context in which we're performing this
   /// conversion, for use in error messages.
   ExprResult PerformImplicitConversion(Expr *From, QualType ToType,
                                        const StandardConversionSequence &SCS,
                                        AssignmentAction Action,
                                        CheckedConversionKind CCK);
 
   bool CheckTypeTraitArity(unsigned Arity, SourceLocation Loc, size_t N);
 
   /// Parsed one of the type trait support pseudo-functions.
   ExprResult ActOnTypeTrait(TypeTrait Kind, SourceLocation KWLoc,
                             ArrayRef<ParsedType> Args,
                             SourceLocation RParenLoc);
   ExprResult BuildTypeTrait(TypeTrait Kind, SourceLocation KWLoc,
                             ArrayRef<TypeSourceInfo *> Args,
                             SourceLocation RParenLoc);
 
   /// ActOnArrayTypeTrait - Parsed one of the binary type trait support
   /// pseudo-functions.
   ExprResult ActOnArrayTypeTrait(ArrayTypeTrait ATT, SourceLocation KWLoc,
                                  ParsedType LhsTy, Expr *DimExpr,
                                  SourceLocation RParen);
 
   ExprResult BuildArrayTypeTrait(ArrayTypeTrait ATT, SourceLocation KWLoc,
                                  TypeSourceInfo *TSInfo, Expr *DimExpr,
                                  SourceLocation RParen);
 
   /// ActOnExpressionTrait - Parsed one of the unary type trait support
   /// pseudo-functions.
   ExprResult ActOnExpressionTrait(ExpressionTrait OET, SourceLocation KWLoc,
                                   Expr *Queried, SourceLocation RParen);
 
   ExprResult BuildExpressionTrait(ExpressionTrait OET, SourceLocation KWLoc,
                                   Expr *Queried, SourceLocation RParen);
 
   QualType CheckPointerToMemberOperands( // C++ 5.5
       ExprResult &LHS, ExprResult &RHS, ExprValueKind &VK, SourceLocation OpLoc,
       bool isIndirect);
   QualType CheckVectorConditionalTypes(ExprResult &Cond, ExprResult &LHS,
                                        ExprResult &RHS,
                                        SourceLocation QuestionLoc);
 
   QualType CheckSizelessVectorConditionalTypes(ExprResult &Cond,
                                                ExprResult &LHS, ExprResult &RHS,
                                                SourceLocation QuestionLoc);
 
   /// Check the operands of ?: under C++ semantics.
   ///
   /// See C++ [expr.cond]. Note that LHS is never null, even for the GNU x ?: y
   /// extension. In this case, LHS == Cond. (But they're not aliases.)
   ///
   /// This function also implements GCC's vector extension and the
   /// OpenCL/ext_vector_type extension for conditionals. The vector extensions
   /// permit the use of a?b:c where the type of a is that of a integer vector
   /// with the same number of elements and size as the vectors of b and c. If
   /// one of either b or c is a scalar it is implicitly converted to match the
   /// type of the vector. Otherwise the expression is ill-formed. If both b and
   /// c are scalars, then b and c are checked and converted to the type of a if
   /// possible.
   ///
   /// The expressions are evaluated differently for GCC's and OpenCL's
   /// extensions. For the GCC extension, the ?: operator is evaluated as
   ///   (a[0] != 0 ? b[0] : c[0], .. , a[n] != 0 ? b[n] : c[n]).
   /// For the OpenCL extensions, the ?: operator is evaluated as
   ///   (most-significant-bit-set(a[0])  ? b[0] : c[0], .. ,
   ///    most-significant-bit-set(a[n]) ? b[n] : c[n]).
   QualType CXXCheckConditionalOperands( // C++ 5.16
       ExprResult &cond, ExprResult &lhs, ExprResult &rhs, ExprValueKind &VK,
       ExprObjectKind &OK, SourceLocation questionLoc);
 
   /// Find a merged pointer type and convert the two expressions to it.
   ///
   /// This finds the composite pointer type for \p E1 and \p E2 according to
   /// C++2a [expr.type]p3. It converts both expressions to this type and returns
   /// it.  It does not emit diagnostics (FIXME: that's not true if \p
   /// ConvertArgs is \c true).
   ///
   /// \param Loc The location of the operator requiring these two expressions to
   /// be converted to the composite pointer type.
   ///
   /// \param ConvertArgs If \c false, do not convert E1 and E2 to the target
   /// type.
   QualType FindCompositePointerType(SourceLocation Loc, Expr *&E1, Expr *&E2,
                                     bool ConvertArgs = true);
   QualType FindCompositePointerType(SourceLocation Loc, ExprResult &E1,
                                     ExprResult &E2, bool ConvertArgs = true) {
     Expr *E1Tmp = E1.get(), *E2Tmp = E2.get();
     QualType Composite =
         FindCompositePointerType(Loc, E1Tmp, E2Tmp, ConvertArgs);
     E1 = E1Tmp;
     E2 = E2Tmp;
     return Composite;
   }
 
   /// MaybeBindToTemporary - If the passed in expression has a record type with
   /// a non-trivial destructor, this will return CXXBindTemporaryExpr. Otherwise
   /// it simply returns the passed in expression.
   ExprResult MaybeBindToTemporary(Expr *E);
 
   /// IgnoredValueConversions - Given that an expression's result is
   /// syntactically ignored, perform any conversions that are
   /// required.
   ExprResult IgnoredValueConversions(Expr *E);
 
   ExprResult CheckUnevaluatedOperand(Expr *E);
 
   /// Process any TypoExprs in the given Expr and its children,
   /// generating diagnostics as appropriate and returning a new Expr if there
   /// were typos that were all successfully corrected and ExprError if one or
   /// more typos could not be corrected.
   ///
   /// \param E The Expr to check for TypoExprs.
   ///
   /// \param InitDecl A VarDecl to avoid because the Expr being corrected is its
   /// initializer.
   ///
   /// \param RecoverUncorrectedTypos If true, when typo correction fails, it
   /// will rebuild the given Expr with all TypoExprs degraded to RecoveryExprs.
   ///
   /// \param Filter A function applied to a newly rebuilt Expr to determine if
   /// it is an acceptable/usable result from a single combination of typo
   /// corrections. As long as the filter returns ExprError, different
   /// combinations of corrections will be tried until all are exhausted.
   ExprResult CorrectDelayedTyposInExpr(
       Expr *E, VarDecl *InitDecl = nullptr,
       bool RecoverUncorrectedTypos = false,
       llvm::function_ref<ExprResult(Expr *)> Filter =
           [](Expr *E) -> ExprResult { return E; });
 
   ExprResult CorrectDelayedTyposInExpr(
       ExprResult ER, VarDecl *InitDecl = nullptr,
       bool RecoverUncorrectedTypos = false,
       llvm::function_ref<ExprResult(Expr *)> Filter =
           [](Expr *E) -> ExprResult { return E; }) {
     return ER.isInvalid()
                ? ER
                : CorrectDelayedTyposInExpr(ER.get(), InitDecl,
                                            RecoverUncorrectedTypos, Filter);
   }
 
   /// Describes the result of an "if-exists" condition check.
   enum IfExistsResult {
     /// The symbol exists.
     IER_Exists,
 
     /// The symbol does not exist.
     IER_DoesNotExist,
 
     /// The name is a dependent name, so the results will differ
     /// from one instantiation to the next.
     IER_Dependent,
 
     /// An error occurred.
     IER_Error
   };
 
   IfExistsResult
   CheckMicrosoftIfExistsSymbol(Scope *S, CXXScopeSpec &SS,
                                const DeclarationNameInfo &TargetNameInfo);
 
   IfExistsResult CheckMicrosoftIfExistsSymbol(Scope *S,
                                               SourceLocation KeywordLoc,
                                               bool IsIfExists, CXXScopeSpec &SS,
                                               UnqualifiedId &Name);
 
   RequiresExprBodyDecl *
   ActOnStartRequiresExpr(SourceLocation RequiresKWLoc,
                          ArrayRef<ParmVarDecl *> LocalParameters,
                          Scope *BodyScope);
   void ActOnFinishRequiresExpr();
   concepts::Requirement *ActOnSimpleRequirement(Expr *E);
   concepts::Requirement *ActOnTypeRequirement(SourceLocation TypenameKWLoc,
                                               CXXScopeSpec &SS,
                                               SourceLocation NameLoc,
                                               const IdentifierInfo *TypeName,
                                               TemplateIdAnnotation *TemplateId);
   concepts::Requirement *ActOnCompoundRequirement(Expr *E,
                                                   SourceLocation NoexceptLoc);
   concepts::Requirement *ActOnCompoundRequirement(
       Expr *E, SourceLocation NoexceptLoc, CXXScopeSpec &SS,
       TemplateIdAnnotation *TypeConstraint, unsigned Depth);
   concepts::Requirement *ActOnNestedRequirement(Expr *Constraint);
   concepts::ExprRequirement *BuildExprRequirement(
       Expr *E, bool IsSatisfied, SourceLocation NoexceptLoc,
       concepts::ExprRequirement::ReturnTypeRequirement ReturnTypeRequirement);
   concepts::ExprRequirement *BuildExprRequirement(
       concepts::Requirement::SubstitutionDiagnostic *ExprSubstDiag,
       bool IsSatisfied, SourceLocation NoexceptLoc,
       concepts::ExprRequirement::ReturnTypeRequirement ReturnTypeRequirement);
   concepts::TypeRequirement *BuildTypeRequirement(TypeSourceInfo *Type);
   concepts::TypeRequirement *BuildTypeRequirement(
       concepts::Requirement::SubstitutionDiagnostic *SubstDiag);
   concepts::NestedRequirement *BuildNestedRequirement(Expr *E);
   concepts::NestedRequirement *
   BuildNestedRequirement(StringRef InvalidConstraintEntity,
                          const ASTConstraintSatisfaction &Satisfaction);
   ExprResult ActOnRequiresExpr(SourceLocation RequiresKWLoc,
                                RequiresExprBodyDecl *Body,
                                SourceLocation LParenLoc,
                                ArrayRef<ParmVarDecl *> LocalParameters,
                                SourceLocation RParenLoc,
                                ArrayRef<concepts::Requirement *> Requirements,
                                SourceLocation ClosingBraceLoc);
 
 private:
   ExprResult BuiltinOperatorNewDeleteOverloaded(ExprResult TheCallResult,
                                                 bool IsDelete);
 
   void AnalyzeDeleteExprMismatch(const CXXDeleteExpr *DE);
   void AnalyzeDeleteExprMismatch(FieldDecl *Field, SourceLocation DeleteLoc,
                                  bool DeleteWasArrayForm);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Member Access Expressions
   /// Implementations are in SemaExprMember.cpp
   ///@{
 
 public:
   /// Check whether an expression might be an implicit class member access.
   bool isPotentialImplicitMemberAccess(const CXXScopeSpec &SS, LookupResult &R,
                                        bool IsAddressOfOperand);
 
   /// Builds an expression which might be an implicit member expression.
   ExprResult BuildPossibleImplicitMemberExpr(
       const CXXScopeSpec &SS, SourceLocation TemplateKWLoc, LookupResult &R,
       const TemplateArgumentListInfo *TemplateArgs, const Scope *S);
 
   /// Builds an implicit member access expression.  The current context
   /// is known to be an instance method, and the given unqualified lookup
   /// set is known to contain only instance members, at least one of which
   /// is from an appropriate type.
   ExprResult
   BuildImplicitMemberExpr(const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                           LookupResult &R,
                           const TemplateArgumentListInfo *TemplateArgs,
                           bool IsDefiniteInstance, const Scope *S);
 
   ExprResult ActOnDependentMemberExpr(
       Expr *Base, QualType BaseType, bool IsArrow, SourceLocation OpLoc,
       const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
       NamedDecl *FirstQualifierInScope, const DeclarationNameInfo &NameInfo,
       const TemplateArgumentListInfo *TemplateArgs);
 
   /// The main callback when the parser finds something like
   ///   expression . [nested-name-specifier] identifier
   ///   expression -> [nested-name-specifier] identifier
   /// where 'identifier' encompasses a fairly broad spectrum of
   /// possibilities, including destructor and operator references.
   ///
   /// \param OpKind either tok::arrow or tok::period
   /// \param ObjCImpDecl the current Objective-C \@implementation
   ///   decl; this is an ugly hack around the fact that Objective-C
   ///   \@implementations aren't properly put in the context chain
   ExprResult ActOnMemberAccessExpr(Scope *S, Expr *Base, SourceLocation OpLoc,
                                    tok::TokenKind OpKind, CXXScopeSpec &SS,
                                    SourceLocation TemplateKWLoc,
                                    UnqualifiedId &Member, Decl *ObjCImpDecl);
 
   MemberExpr *
   BuildMemberExpr(Expr *Base, bool IsArrow, SourceLocation OpLoc,
                   NestedNameSpecifierLoc NNS, SourceLocation TemplateKWLoc,
                   ValueDecl *Member, DeclAccessPair FoundDecl,
                   bool HadMultipleCandidates,
                   const DeclarationNameInfo &MemberNameInfo, QualType Ty,
                   ExprValueKind VK, ExprObjectKind OK,
                   const TemplateArgumentListInfo *TemplateArgs = nullptr);
 
   // Check whether the declarations we found through a nested-name
   // specifier in a member expression are actually members of the base
   // type.  The restriction here is:
   //
   //   C++ [expr.ref]p2:
   //     ... In these cases, the id-expression shall name a
   //     member of the class or of one of its base classes.
   //
   // So it's perfectly legitimate for the nested-name specifier to name
   // an unrelated class, and for us to find an overload set including
   // decls from classes which are not superclasses, as long as the decl
   // we actually pick through overload resolution is from a superclass.
   bool CheckQualifiedMemberReference(Expr *BaseExpr, QualType BaseType,
                                      const CXXScopeSpec &SS,
                                      const LookupResult &R);
 
   // This struct is for use by ActOnMemberAccess to allow
   // BuildMemberReferenceExpr to be able to reinvoke ActOnMemberAccess after
   // changing the access operator from a '.' to a '->' (to see if that is the
   // change needed to fix an error about an unknown member, e.g. when the class
   // defines a custom operator->).
   struct ActOnMemberAccessExtraArgs {
     Scope *S;
     UnqualifiedId &Id;
     Decl *ObjCImpDecl;
   };
 
   ExprResult BuildMemberReferenceExpr(
       Expr *Base, QualType BaseType, SourceLocation OpLoc, bool IsArrow,
       CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
       NamedDecl *FirstQualifierInScope, const DeclarationNameInfo &NameInfo,
       const TemplateArgumentListInfo *TemplateArgs, const Scope *S,
       ActOnMemberAccessExtraArgs *ExtraArgs = nullptr);
 
   ExprResult
   BuildMemberReferenceExpr(Expr *Base, QualType BaseType, SourceLocation OpLoc,
                            bool IsArrow, const CXXScopeSpec &SS,
                            SourceLocation TemplateKWLoc,
                            NamedDecl *FirstQualifierInScope, LookupResult &R,
                            const TemplateArgumentListInfo *TemplateArgs,
                            const Scope *S, bool SuppressQualifierCheck = false,
                            ActOnMemberAccessExtraArgs *ExtraArgs = nullptr);
 
   ExprResult BuildFieldReferenceExpr(Expr *BaseExpr, bool IsArrow,
                                      SourceLocation OpLoc,
                                      const CXXScopeSpec &SS, FieldDecl *Field,
                                      DeclAccessPair FoundDecl,
                                      const DeclarationNameInfo &MemberNameInfo);
 
   /// Perform conversions on the LHS of a member access expression.
   ExprResult PerformMemberExprBaseConversion(Expr *Base, bool IsArrow);
 
   ExprResult BuildAnonymousStructUnionMemberReference(
       const CXXScopeSpec &SS, SourceLocation nameLoc,
       IndirectFieldDecl *indirectField,
       DeclAccessPair FoundDecl = DeclAccessPair::make(nullptr, AS_none),
       Expr *baseObjectExpr = nullptr, SourceLocation opLoc = SourceLocation());
 
 private:
   void CheckMemberAccessOfNoDeref(const MemberExpr *E);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Initializers
   /// Implementations are in SemaInit.cpp
   ///@{
 
 public:
   /// Stack of types that correspond to the parameter entities that are
   /// currently being copy-initialized. Can be empty.
   llvm::SmallVector<QualType, 4> CurrentParameterCopyTypes;
 
   llvm::DenseMap<unsigned, CXXDeductionGuideDecl *>
       AggregateDeductionCandidates;
 
   bool IsStringInit(Expr *Init, const ArrayType *AT);
 
   /// Determine whether we can perform aggregate initialization for the purposes
   /// of overload resolution.
   bool CanPerformAggregateInitializationForOverloadResolution(
       const InitializedEntity &Entity, InitListExpr *From);
 
   ExprResult ActOnDesignatedInitializer(Designation &Desig,
                                         SourceLocation EqualOrColonLoc,
                                         bool GNUSyntax, ExprResult Init);
 
   /// Check that the lifetime of the initializer (and its subobjects) is
   /// sufficient for initializing the entity, and perform lifetime extension
   /// (when permitted) if not.
   void checkInitializerLifetime(const InitializedEntity &Entity, Expr *Init);
 
   MaterializeTemporaryExpr *
   CreateMaterializeTemporaryExpr(QualType T, Expr *Temporary,
                                  bool BoundToLvalueReference);
 
   /// If \p E is a prvalue denoting an unmaterialized temporary, materialize
   /// it as an xvalue. In C++98, the result will still be a prvalue, because
   /// we don't have xvalues there.
   ExprResult TemporaryMaterializationConversion(Expr *E);
 
   ExprResult PerformQualificationConversion(
       Expr *E, QualType Ty, ExprValueKind VK = VK_PRValue,
       CheckedConversionKind CCK = CheckedConversionKind::Implicit);
 
   bool CanPerformCopyInitialization(const InitializedEntity &Entity,
                                     ExprResult Init);
   ExprResult PerformCopyInitialization(const InitializedEntity &Entity,
                                        SourceLocation EqualLoc, ExprResult Init,
                                        bool TopLevelOfInitList = false,
                                        bool AllowExplicit = false);
 
   QualType DeduceTemplateSpecializationFromInitializer(
       TypeSourceInfo *TInfo, const InitializedEntity &Entity,
       const InitializationKind &Kind, MultiExprArg Init);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Lambda Expressions
   /// Implementations are in SemaLambda.cpp
   ///@{
 
 public:
   /// Create a new lambda closure type.
   CXXRecordDecl *createLambdaClosureType(SourceRange IntroducerRange,
                                          TypeSourceInfo *Info,
                                          unsigned LambdaDependencyKind,
                                          LambdaCaptureDefault CaptureDefault);
 
   /// Number lambda for linkage purposes if necessary.
   void handleLambdaNumbering(CXXRecordDecl *Class, CXXMethodDecl *Method,
                              std::optional<CXXRecordDecl::LambdaNumbering>
                                  NumberingOverride = std::nullopt);
 
   /// Endow the lambda scope info with the relevant properties.
   void buildLambdaScope(sema::LambdaScopeInfo *LSI, CXXMethodDecl *CallOperator,
                         SourceRange IntroducerRange,
                         LambdaCaptureDefault CaptureDefault,
                         SourceLocation CaptureDefaultLoc, bool ExplicitParams,
                         bool Mutable);
 
   CXXMethodDecl *CreateLambdaCallOperator(SourceRange IntroducerRange,
                                           CXXRecordDecl *Class);
 
   void AddTemplateParametersToLambdaCallOperator(
       CXXMethodDecl *CallOperator, CXXRecordDecl *Class,
       TemplateParameterList *TemplateParams);
 
   void CompleteLambdaCallOperator(
       CXXMethodDecl *Method, SourceLocation LambdaLoc,
       SourceLocation CallOperatorLoc, Expr *TrailingRequiresClause,
       TypeSourceInfo *MethodTyInfo, ConstexprSpecKind ConstexprKind,
       StorageClass SC, ArrayRef<ParmVarDecl *> Params,
       bool HasExplicitResultType);
 
   /// Returns true if the explicit object parameter was invalid.
   bool DiagnoseInvalidExplicitObjectParameterInLambda(CXXMethodDecl *Method,
                                                       SourceLocation CallLoc);
 
   /// Perform initialization analysis of the init-capture and perform
   /// any implicit conversions such as an lvalue-to-rvalue conversion if
   /// not being used to initialize a reference.
   ParsedType actOnLambdaInitCaptureInitialization(
       SourceLocation Loc, bool ByRef, SourceLocation EllipsisLoc,
       IdentifierInfo *Id, LambdaCaptureInitKind InitKind, Expr *&Init) {
     return ParsedType::make(buildLambdaInitCaptureInitialization(
         Loc, ByRef, EllipsisLoc, std::nullopt, Id,
         InitKind != LambdaCaptureInitKind::CopyInit, Init));
   }
   QualType buildLambdaInitCaptureInitialization(
       SourceLocation Loc, bool ByRef, SourceLocation EllipsisLoc,
       std::optional<unsigned> NumExpansions, IdentifierInfo *Id,
       bool DirectInit, Expr *&Init);
 
   /// Create a dummy variable within the declcontext of the lambda's
   ///  call operator, for name lookup purposes for a lambda init capture.
   ///
   ///  CodeGen handles emission of lambda captures, ignoring these dummy
   ///  variables appropriately.
   VarDecl *createLambdaInitCaptureVarDecl(
       SourceLocation Loc, QualType InitCaptureType, SourceLocation EllipsisLoc,
       IdentifierInfo *Id, unsigned InitStyle, Expr *Init, DeclContext *DeclCtx);
 
   /// Add an init-capture to a lambda scope.
   void addInitCapture(sema::LambdaScopeInfo *LSI, VarDecl *Var, bool ByRef);
 
   /// Note that we have finished the explicit captures for the
   /// given lambda.
   void finishLambdaExplicitCaptures(sema::LambdaScopeInfo *LSI);
 
   /// Deduce a block or lambda's return type based on the return
   /// statements present in the body.
   void deduceClosureReturnType(sema::CapturingScopeInfo &CSI);
 
   /// Once the Lambdas capture are known, we can start to create the closure,
   /// call operator method, and keep track of the captures.
   /// We do the capture lookup here, but they are not actually captured until
   /// after we know what the qualifiers of the call operator are.
   void ActOnLambdaExpressionAfterIntroducer(LambdaIntroducer &Intro,
                                             Scope *CurContext);
 
   /// This is called after parsing the explicit template parameter list
   /// on a lambda (if it exists) in C++2a.
   void ActOnLambdaExplicitTemplateParameterList(LambdaIntroducer &Intro,
                                                 SourceLocation LAngleLoc,
                                                 ArrayRef<NamedDecl *> TParams,
                                                 SourceLocation RAngleLoc,
                                                 ExprResult RequiresClause);
 
   void ActOnLambdaClosureQualifiers(LambdaIntroducer &Intro,
                                     SourceLocation MutableLoc);
 
   void ActOnLambdaClosureParameters(
       Scope *LambdaScope,
       MutableArrayRef<DeclaratorChunk::ParamInfo> ParamInfo);
 
   /// ActOnStartOfLambdaDefinition - This is called just before we start
   /// parsing the body of a lambda; it analyzes the explicit captures and
   /// arguments, and sets up various data-structures for the body of the
   /// lambda.
   void ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
                                     Declarator &ParamInfo, const DeclSpec &DS);
 
   /// ActOnLambdaError - If there is an error parsing a lambda, this callback
   /// is invoked to pop the information about the lambda.
   void ActOnLambdaError(SourceLocation StartLoc, Scope *CurScope,
                         bool IsInstantiation = false);
 
   /// ActOnLambdaExpr - This is called when the body of a lambda expression
   /// was successfully completed.
   ExprResult ActOnLambdaExpr(SourceLocation StartLoc, Stmt *Body);
 
   /// Does copying/destroying the captured variable have side effects?
   bool CaptureHasSideEffects(const sema::Capture &From);
 
   /// Diagnose if an explicit lambda capture is unused. Returns true if a
   /// diagnostic is emitted.
   bool DiagnoseUnusedLambdaCapture(SourceRange CaptureRange,
                                    const sema::Capture &From);
 
   /// Build a FieldDecl suitable to hold the given capture.
   FieldDecl *BuildCaptureField(RecordDecl *RD, const sema::Capture &Capture);
 
   /// Initialize the given capture with a suitable expression.
   ExprResult BuildCaptureInit(const sema::Capture &Capture,
                               SourceLocation ImplicitCaptureLoc,
                               bool IsOpenMPMapping = false);
 
   /// Complete a lambda-expression having processed and attached the
   /// lambda body.
   ExprResult BuildLambdaExpr(SourceLocation StartLoc, SourceLocation EndLoc,
                              sema::LambdaScopeInfo *LSI);
 
   /// Get the return type to use for a lambda's conversion function(s) to
   /// function pointer type, given the type of the call operator.
   QualType
   getLambdaConversionFunctionResultType(const FunctionProtoType *CallOpType,
                                         CallingConv CC);
 
   ExprResult BuildBlockForLambdaConversion(SourceLocation CurrentLocation,
                                            SourceLocation ConvLocation,
                                            CXXConversionDecl *Conv, Expr *Src);
 
   class LambdaScopeForCallOperatorInstantiationRAII
       : private FunctionScopeRAII {
   public:
     LambdaScopeForCallOperatorInstantiationRAII(
         Sema &SemasRef, FunctionDecl *FD, MultiLevelTemplateArgumentList MLTAL,
         LocalInstantiationScope &Scope,
         bool ShouldAddDeclsFromParentScope = true);
   };
 
   /// Compute the mangling number context for a lambda expression or
   /// block literal. Also return the extra mangling decl if any.
   ///
   /// \param DC - The DeclContext containing the lambda expression or
   /// block literal.
   std::tuple<MangleNumberingContext *, Decl *>
   getCurrentMangleNumberContext(const DeclContext *DC);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Name Lookup
   ///
   /// These routines provide name lookup that is used during semantic
   /// analysis to resolve the various kinds of names (identifiers,
   /// overloaded operator names, constructor names, etc.) into zero or
   /// more declarations within a particular scope. The major entry
   /// points are LookupName, which performs unqualified name lookup,
   /// and LookupQualifiedName, which performs qualified name lookup.
   ///
   /// All name lookup is performed based on some specific criteria,
   /// which specify what names will be visible to name lookup and how
   /// far name lookup should work. These criteria are important both
   /// for capturing language semantics (certain lookups will ignore
   /// certain names, for example) and for performance, since name
   /// lookup is often a bottleneck in the compilation of C++. Name
   /// lookup criteria is specified via the LookupCriteria enumeration.
   ///
   /// The results of name lookup can vary based on the kind of name
   /// lookup performed, the current language, and the translation
   /// unit. In C, for example, name lookup will either return nothing
   /// (no entity found) or a single declaration. In C++, name lookup
   /// can additionally refer to a set of overloaded functions or
   /// result in an ambiguity. All of the possible results of name
   /// lookup are captured by the LookupResult class, which provides
   /// the ability to distinguish among them.
   ///
   /// Implementations are in SemaLookup.cpp
   ///@{
 
 public:
   /// Tracks whether we are in a context where typo correction is
   /// disabled.
   bool DisableTypoCorrection;
 
   /// The number of typos corrected by CorrectTypo.
   unsigned TyposCorrected;
 
   typedef llvm::SmallSet<SourceLocation, 2> SrcLocSet;
   typedef llvm::DenseMap<IdentifierInfo *, SrcLocSet> IdentifierSourceLocations;
 
   /// A cache containing identifiers for which typo correction failed and
   /// their locations, so that repeated attempts to correct an identifier in a
   /// given location are ignored if typo correction already failed for it.
   IdentifierSourceLocations TypoCorrectionFailures;
 
   /// SpecialMemberOverloadResult - The overloading result for a special member
   /// function.
   ///
   /// This is basically a wrapper around PointerIntPair. The lowest bits of the
   /// integer are used to determine whether overload resolution succeeded.
   class SpecialMemberOverloadResult {
   public:
     enum Kind { NoMemberOrDeleted, Ambiguous, Success };
 
   private:
     llvm::PointerIntPair<CXXMethodDecl *, 2> Pair;
 
   public:
     SpecialMemberOverloadResult() {}
     SpecialMemberOverloadResult(CXXMethodDecl *MD)
         : Pair(MD, MD->isDeleted() ? NoMemberOrDeleted : Success) {}
 
     CXXMethodDecl *getMethod() const { return Pair.getPointer(); }
     void setMethod(CXXMethodDecl *MD) { Pair.setPointer(MD); }
 
     Kind getKind() const { return static_cast<Kind>(Pair.getInt()); }
     void setKind(Kind K) { Pair.setInt(K); }
   };
 
   class SpecialMemberOverloadResultEntry : public llvm::FastFoldingSetNode,
                                            public SpecialMemberOverloadResult {
   public:
     SpecialMemberOverloadResultEntry(const llvm::FoldingSetNodeID &ID)
         : FastFoldingSetNode(ID) {}
   };
 
   /// A cache of special member function overload resolution results
   /// for C++ records.
   llvm::FoldingSet<SpecialMemberOverloadResultEntry> SpecialMemberCache;
 
   /// Holds TypoExprs that are created from `createDelayedTypo`. This is used by
   /// `TransformTypos` in order to keep track of any TypoExprs that are created
   /// recursively during typo correction and wipe them away if the correction
   /// fails.
   llvm::SmallVector<TypoExpr *, 2> TypoExprs;
 
   enum class AcceptableKind { Visible, Reachable };
 
   // Members have to be NamespaceDecl* or TranslationUnitDecl*.
   // TODO: make this is a typesafe union.
   typedef llvm::SmallSetVector<DeclContext *, 16> AssociatedNamespaceSet;
   typedef llvm::SmallSetVector<CXXRecordDecl *, 16> AssociatedClassSet;
 
   /// Describes the kind of name lookup to perform.
   enum LookupNameKind {
     /// Ordinary name lookup, which finds ordinary names (functions,
     /// variables, typedefs, etc.) in C and most kinds of names
     /// (functions, variables, members, types, etc.) in C++.
     LookupOrdinaryName = 0,
     /// Tag name lookup, which finds the names of enums, classes,
     /// structs, and unions.
     LookupTagName,
     /// Label name lookup.
     LookupLabel,
     /// Member name lookup, which finds the names of
     /// class/struct/union members.
     LookupMemberName,
     /// Look up of an operator name (e.g., operator+) for use with
     /// operator overloading. This lookup is similar to ordinary name
     /// lookup, but will ignore any declarations that are class members.
     LookupOperatorName,
     /// Look up a name following ~ in a destructor name. This is an ordinary
     /// lookup, but prefers tags to typedefs.
     LookupDestructorName,
     /// Look up of a name that precedes the '::' scope resolution
     /// operator in C++. This lookup completely ignores operator, object,
     /// function, and enumerator names (C++ [basic.lookup.qual]p1).
     LookupNestedNameSpecifierName,
     /// Look up a namespace name within a C++ using directive or
     /// namespace alias definition, ignoring non-namespace names (C++
     /// [basic.lookup.udir]p1).
     LookupNamespaceName,
     /// Look up all declarations in a scope with the given name,
     /// including resolved using declarations.  This is appropriate
     /// for checking redeclarations for a using declaration.
     LookupUsingDeclName,
     /// Look up an ordinary name that is going to be redeclared as a
     /// name with linkage. This lookup ignores any declarations that
     /// are outside of the current scope unless they have linkage. See
     /// C99 6.2.2p4-5 and C++ [basic.link]p6.
     LookupRedeclarationWithLinkage,
     /// Look up a friend of a local class. This lookup does not look
     /// outside the innermost non-class scope. See C++11 [class.friend]p11.
     LookupLocalFriendName,
     /// Look up the name of an Objective-C protocol.
     LookupObjCProtocolName,
     /// Look up implicit 'self' parameter of an objective-c method.
     LookupObjCImplicitSelfParam,
     /// Look up the name of an OpenMP user-defined reduction operation.
     LookupOMPReductionName,
     /// Look up the name of an OpenMP user-defined mapper.
     LookupOMPMapperName,
     /// Look up any declaration with any name.
     LookupAnyName
   };
 
   /// The possible outcomes of name lookup for a literal operator.
   enum LiteralOperatorLookupResult {
     /// The lookup resulted in an error.
     LOLR_Error,
     /// The lookup found no match but no diagnostic was issued.
     LOLR_ErrorNoDiagnostic,
     /// The lookup found a single 'cooked' literal operator, which
     /// expects a normal literal to be built and passed to it.
     LOLR_Cooked,
     /// The lookup found a single 'raw' literal operator, which expects
     /// a string literal containing the spelling of the literal token.
     LOLR_Raw,
     /// The lookup found an overload set of literal operator templates,
     /// which expect the characters of the spelling of the literal token to be
     /// passed as a non-type template argument pack.
     LOLR_Template,
     /// The lookup found an overload set of literal operator templates,
     /// which expect the character type and characters of the spelling of the
     /// string literal token to be passed as template arguments.
     LOLR_StringTemplatePack,
   };
 
   SpecialMemberOverloadResult
   LookupSpecialMember(CXXRecordDecl *D, CXXSpecialMemberKind SM, bool ConstArg,
                       bool VolatileArg, bool RValueThis, bool ConstThis,
                       bool VolatileThis);
 
   typedef std::function<void(const TypoCorrection &)> TypoDiagnosticGenerator;
   typedef std::function<ExprResult(Sema &, TypoExpr *, TypoCorrection)>
       TypoRecoveryCallback;
 
   RedeclarationKind forRedeclarationInCurContext() const;
 
   /// Look up a name, looking for a single declaration.  Return
   /// null if the results were absent, ambiguous, or overloaded.
   ///
   /// It is preferable to use the elaborated form and explicitly handle
   /// ambiguity and overloaded.
   NamedDecl *LookupSingleName(
       Scope *S, DeclarationName Name, SourceLocation Loc,
       LookupNameKind NameKind,
       RedeclarationKind Redecl = RedeclarationKind::NotForRedeclaration);
 
   /// Lookup a builtin function, when name lookup would otherwise
   /// fail.
   bool LookupBuiltin(LookupResult &R);
   void LookupNecessaryTypesForBuiltin(Scope *S, unsigned ID);
 
   /// Perform unqualified name lookup starting from a given
   /// scope.
   ///
   /// Unqualified name lookup (C++ [basic.lookup.unqual], C99 6.2.1) is
   /// used to find names within the current scope. For example, 'x' in
   /// @code
   /// int x;
   /// int f() {
   ///   return x; // unqualified name look finds 'x' in the global scope
   /// }
   /// @endcode
   ///
   /// Different lookup criteria can find different names. For example, a
   /// particular scope can have both a struct and a function of the same
   /// name, and each can be found by certain lookup criteria. For more
   /// information about lookup criteria, see the documentation for the
   /// class LookupCriteria.
   ///
   /// @param S        The scope from which unqualified name lookup will
   /// begin. If the lookup criteria permits, name lookup may also search
   /// in the parent scopes.
   ///
   /// @param [in,out] R Specifies the lookup to perform (e.g., the name to
   /// look up and the lookup kind), and is updated with the results of lookup
   /// including zero or more declarations and possibly additional information
   /// used to diagnose ambiguities.
   ///
   /// @returns \c true if lookup succeeded and false otherwise.
   bool LookupName(LookupResult &R, Scope *S, bool AllowBuiltinCreation = false,
                   bool ForceNoCPlusPlus = false);
 
   /// Perform qualified name lookup into a given context.
   ///
   /// Qualified name lookup (C++ [basic.lookup.qual]) is used to find
   /// names when the context of those names is explicit specified, e.g.,
   /// "std::vector" or "x->member", or as part of unqualified name lookup.
   ///
   /// Different lookup criteria can find different names. For example, a
   /// particular scope can have both a struct and a function of the same
   /// name, and each can be found by certain lookup criteria. For more
   /// information about lookup criteria, see the documentation for the
   /// class LookupCriteria.
   ///
   /// \param R captures both the lookup criteria and any lookup results found.
   ///
   /// \param LookupCtx The context in which qualified name lookup will
   /// search. If the lookup criteria permits, name lookup may also search
   /// in the parent contexts or (for C++ classes) base classes.
   ///
   /// \param InUnqualifiedLookup true if this is qualified name lookup that
   /// occurs as part of unqualified name lookup.
   ///
   /// \returns true if lookup succeeded, false if it failed.
   bool LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
                            bool InUnqualifiedLookup = false);
 
   /// Performs qualified name lookup or special type of lookup for
   /// "__super::" scope specifier.
   ///
   /// This routine is a convenience overload meant to be called from contexts
   /// that need to perform a qualified name lookup with an optional C++ scope
   /// specifier that might require special kind of lookup.
   ///
   /// \param R captures both the lookup criteria and any lookup results found.
   ///
   /// \param LookupCtx The context in which qualified name lookup will
   /// search.
   ///
   /// \param SS An optional C++ scope-specifier.
   ///
   /// \returns true if lookup succeeded, false if it failed.
   bool LookupQualifiedName(LookupResult &R, DeclContext *LookupCtx,
                            CXXScopeSpec &SS);
 
   /// Performs name lookup for a name that was parsed in the
   /// source code, and may contain a C++ scope specifier.
   ///
   /// This routine is a convenience routine meant to be called from
   /// contexts that receive a name and an optional C++ scope specifier
   /// (e.g., "N::M::x"). It will then perform either qualified or
   /// unqualified name lookup (with LookupQualifiedName or LookupName,
   /// respectively) on the given name and return those results. It will
   /// perform a special type of lookup for "__super::" scope specifier.
   ///
   /// @param S        The scope from which unqualified name lookup will
   /// begin.
   ///
   /// @param SS       An optional C++ scope-specifier, e.g., "::N::M".
   ///
   /// @param EnteringContext Indicates whether we are going to enter the
   /// context of the scope-specifier SS (if present).
   ///
   /// @returns True if any decls were found (but possibly ambiguous)
   bool LookupParsedName(LookupResult &R, Scope *S, CXXScopeSpec *SS,
                         QualType ObjectType, bool AllowBuiltinCreation = false,
                         bool EnteringContext = false);
 
   /// Perform qualified name lookup into all base classes of the given
   /// class.
   ///
   /// \param R captures both the lookup criteria and any lookup results found.
   ///
   /// \param Class The context in which qualified name lookup will
   /// search. Name lookup will search in all base classes merging the results.
   ///
   /// @returns True if any decls were found (but possibly ambiguous)
   bool LookupInSuper(LookupResult &R, CXXRecordDecl *Class);
 
   void LookupOverloadedOperatorName(OverloadedOperatorKind Op, Scope *S,
                                     UnresolvedSetImpl &Functions);
 
   /// LookupOrCreateLabel - Do a name lookup of a label with the specified name.
   /// If GnuLabelLoc is a valid source location, then this is a definition
   /// of an __label__ label name, otherwise it is a normal label definition
   /// or use.
   LabelDecl *LookupOrCreateLabel(IdentifierInfo *II, SourceLocation IdentLoc,
                                  SourceLocation GnuLabelLoc = SourceLocation());
 
   /// Look up the constructors for the given class.
   DeclContextLookupResult LookupConstructors(CXXRecordDecl *Class);
 
   /// Look up the default constructor for the given class.
   CXXConstructorDecl *LookupDefaultConstructor(CXXRecordDecl *Class);
 
   /// Look up the copying constructor for the given class.
   CXXConstructorDecl *LookupCopyingConstructor(CXXRecordDecl *Class,
                                                unsigned Quals);
 
   /// Look up the copying assignment operator for the given class.
   CXXMethodDecl *LookupCopyingAssignment(CXXRecordDecl *Class, unsigned Quals,
                                          bool RValueThis, unsigned ThisQuals);
 
   /// Look up the moving constructor for the given class.
   CXXConstructorDecl *LookupMovingConstructor(CXXRecordDecl *Class,
                                               unsigned Quals);
 
   /// Look up the moving assignment operator for the given class.
   CXXMethodDecl *LookupMovingAssignment(CXXRecordDecl *Class, unsigned Quals,
                                         bool RValueThis, unsigned ThisQuals);
 
   /// Look for the destructor of the given class.
   ///
   /// During semantic analysis, this routine should be used in lieu of
   /// CXXRecordDecl::getDestructor().
   ///
   /// \returns The destructor for this class.
   CXXDestructorDecl *LookupDestructor(CXXRecordDecl *Class);
 
   /// Force the declaration of any implicitly-declared members of this
   /// class.
   void ForceDeclarationOfImplicitMembers(CXXRecordDecl *Class);
 
   /// Make a merged definition of an existing hidden definition \p ND
   /// visible at the specified location.
   void makeMergedDefinitionVisible(NamedDecl *ND);
 
   /// Check ODR hashes for C/ObjC when merging types from modules.
   /// Differently from C++, actually parse the body and reject in case
   /// of a mismatch.
   template <typename T,
             typename = std::enable_if_t<std::is_base_of<NamedDecl, T>::value>>
   bool ActOnDuplicateODRHashDefinition(T *Duplicate, T *Previous) {
     if (Duplicate->getODRHash() != Previous->getODRHash())
       return false;
 
     // Make the previous decl visible.
     makeMergedDefinitionVisible(Previous);
     return true;
   }
 
   /// Get the set of additional modules that should be checked during
   /// name lookup. A module and its imports become visible when instanting a
   /// template defined within it.
   llvm::DenseSet<Module *> &getLookupModules();
 
   bool hasVisibleMergedDefinition(const NamedDecl *Def);
   bool hasMergedDefinitionInCurrentModule(const NamedDecl *Def);
 
   /// Determine if the template parameter \p D has a visible default argument.
   bool
   hasVisibleDefaultArgument(const NamedDecl *D,
                             llvm::SmallVectorImpl<Module *> *Modules = nullptr);
   /// Determine if the template parameter \p D has a reachable default argument.
   bool hasReachableDefaultArgument(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
   /// Determine if the template parameter \p D has a reachable default argument.
   bool hasAcceptableDefaultArgument(const NamedDecl *D,
                                     llvm::SmallVectorImpl<Module *> *Modules,
                                     Sema::AcceptableKind Kind);
 
   /// Determine if there is a visible declaration of \p D that is an explicit
   /// specialization declaration for a specialization of a template. (For a
   /// member specialization, use hasVisibleMemberSpecialization.)
   bool hasVisibleExplicitSpecialization(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
   /// Determine if there is a reachable declaration of \p D that is an explicit
   /// specialization declaration for a specialization of a template. (For a
   /// member specialization, use hasReachableMemberSpecialization.)
   bool hasReachableExplicitSpecialization(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
 
   /// Determine if there is a visible declaration of \p D that is a member
   /// specialization declaration (as opposed to an instantiated declaration).
   bool hasVisibleMemberSpecialization(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
   /// Determine if there is a reachable declaration of \p D that is a member
   /// specialization declaration (as opposed to an instantiated declaration).
   bool hasReachableMemberSpecialization(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
 
   bool isModuleVisible(const Module *M, bool ModulePrivate = false);
 
   /// Determine whether any declaration of an entity is visible.
   bool
   hasVisibleDeclaration(const NamedDecl *D,
                         llvm::SmallVectorImpl<Module *> *Modules = nullptr) {
     return isVisible(D) || hasVisibleDeclarationSlow(D, Modules);
   }
 
   bool hasVisibleDeclarationSlow(const NamedDecl *D,
                                  llvm::SmallVectorImpl<Module *> *Modules);
   /// Determine whether any declaration of an entity is reachable.
   bool
   hasReachableDeclaration(const NamedDecl *D,
                           llvm::SmallVectorImpl<Module *> *Modules = nullptr) {
     return isReachable(D) || hasReachableDeclarationSlow(D, Modules);
   }
   bool hasReachableDeclarationSlow(
       const NamedDecl *D, llvm::SmallVectorImpl<Module *> *Modules = nullptr);
 
   void diagnoseTypo(const TypoCorrection &Correction,
                     const PartialDiagnostic &TypoDiag,
                     bool ErrorRecovery = true);
 
   /// Diagnose a successfully-corrected typo. Separated from the correction
   /// itself to allow external validation of the result, etc.
   ///
   /// \param Correction The result of performing typo correction.
   /// \param TypoDiag The diagnostic to produce. This will have the corrected
   ///        string added to it (and usually also a fixit).
   /// \param PrevNote A note to use when indicating the location of the entity
   ///        to which we are correcting. Will have the correction string added
   ///        to it.
   /// \param ErrorRecovery If \c true (the default), the caller is going to
   ///        recover from the typo as if the corrected string had been typed.
   ///        In this case, \c PDiag must be an error, and we will attach a fixit
   ///        to it.
   void diagnoseTypo(const TypoCorrection &Correction,
                     const PartialDiagnostic &TypoDiag,
                     const PartialDiagnostic &PrevNote,
                     bool ErrorRecovery = true);
 
   /// Find the associated classes and namespaces for
   /// argument-dependent lookup for a call with the given set of
   /// arguments.
   ///
   /// This routine computes the sets of associated classes and associated
   /// namespaces searched by argument-dependent lookup
   /// (C++ [basic.lookup.argdep]) for a given set of arguments.
   void FindAssociatedClassesAndNamespaces(
       SourceLocation InstantiationLoc, ArrayRef<Expr *> Args,
       AssociatedNamespaceSet &AssociatedNamespaces,
       AssociatedClassSet &AssociatedClasses);
 
   /// Produce a diagnostic describing the ambiguity that resulted
   /// from name lookup.
   ///
   /// \param Result The result of the ambiguous lookup to be diagnosed.
   void DiagnoseAmbiguousLookup(LookupResult &Result);
 
   /// LookupLiteralOperator - Determine which literal operator should be used
   /// for a user-defined literal, per C++11 [lex.ext].
   ///
   /// Normal overload resolution is not used to select which literal operator to
   /// call for a user-defined literal. Look up the provided literal operator
   /// name, and filter the results to the appropriate set for the given argument
   /// types.
   LiteralOperatorLookupResult
   LookupLiteralOperator(Scope *S, LookupResult &R, ArrayRef<QualType> ArgTys,
                         bool AllowRaw, bool AllowTemplate,
                         bool AllowStringTemplate, bool DiagnoseMissing,
                         StringLiteral *StringLit = nullptr);
 
   void ArgumentDependentLookup(DeclarationName Name, SourceLocation Loc,
                                ArrayRef<Expr *> Args, ADLResult &Functions);
 
   void LookupVisibleDecls(Scope *S, LookupNameKind Kind,
                           VisibleDeclConsumer &Consumer,
                           bool IncludeGlobalScope = true,
                           bool LoadExternal = true);
   void LookupVisibleDecls(DeclContext *Ctx, LookupNameKind Kind,
                           VisibleDeclConsumer &Consumer,
                           bool IncludeGlobalScope = true,
                           bool IncludeDependentBases = false,
                           bool LoadExternal = true);
 
   enum CorrectTypoKind {
     CTK_NonError,     // CorrectTypo used in a non error recovery situation.
     CTK_ErrorRecovery // CorrectTypo used in normal error recovery.
   };
 
   /// Try to "correct" a typo in the source code by finding
   /// visible declarations whose names are similar to the name that was
   /// present in the source code.
   ///
   /// \param TypoName the \c DeclarationNameInfo structure that contains
   /// the name that was present in the source code along with its location.
   ///
   /// \param LookupKind the name-lookup criteria used to search for the name.
   ///
   /// \param S the scope in which name lookup occurs.
   ///
   /// \param SS the nested-name-specifier that precedes the name we're
   /// looking for, if present.
   ///
   /// \param CCC A CorrectionCandidateCallback object that provides further
   /// validation of typo correction candidates. It also provides flags for
   /// determining the set of keywords permitted.
   ///
   /// \param MemberContext if non-NULL, the context in which to look for
   /// a member access expression.
   ///
   /// \param EnteringContext whether we're entering the context described by
   /// the nested-name-specifier SS.
   ///
   /// \param OPT when non-NULL, the search for visible declarations will
   /// also walk the protocols in the qualified interfaces of \p OPT.
   ///
   /// \returns a \c TypoCorrection containing the corrected name if the typo
   /// along with information such as the \c NamedDecl where the corrected name
   /// was declared, and any additional \c NestedNameSpecifier needed to access
   /// it (C++ only). The \c TypoCorrection is empty if there is no correction.
   TypoCorrection CorrectTypo(const DeclarationNameInfo &Typo,
                              Sema::LookupNameKind LookupKind, Scope *S,
                              CXXScopeSpec *SS, CorrectionCandidateCallback &CCC,
                              CorrectTypoKind Mode,
                              DeclContext *MemberContext = nullptr,
                              bool EnteringContext = false,
                              const ObjCObjectPointerType *OPT = nullptr,
                              bool RecordFailure = true);
 
   /// Try to "correct" a typo in the source code by finding
   /// visible declarations whose names are similar to the name that was
   /// present in the source code.
   ///
   /// \param TypoName the \c DeclarationNameInfo structure that contains
   /// the name that was present in the source code along with its location.
   ///
   /// \param LookupKind the name-lookup criteria used to search for the name.
   ///
   /// \param S the scope in which name lookup occurs.
   ///
   /// \param SS the nested-name-specifier that precedes the name we're
   /// looking for, if present.
   ///
   /// \param CCC A CorrectionCandidateCallback object that provides further
   /// validation of typo correction candidates. It also provides flags for
   /// determining the set of keywords permitted.
   ///
   /// \param TDG A TypoDiagnosticGenerator functor that will be used to print
   /// diagnostics when the actual typo correction is attempted.
   ///
   /// \param TRC A TypoRecoveryCallback functor that will be used to build an
   /// Expr from a typo correction candidate.
   ///
   /// \param MemberContext if non-NULL, the context in which to look for
   /// a member access expression.
   ///
   /// \param EnteringContext whether we're entering the context described by
   /// the nested-name-specifier SS.
   ///
   /// \param OPT when non-NULL, the search for visible declarations will
   /// also walk the protocols in the qualified interfaces of \p OPT.
   ///
   /// \returns a new \c TypoExpr that will later be replaced in the AST with an
   /// Expr representing the result of performing typo correction, or nullptr if
   /// typo correction is not possible. If nullptr is returned, no diagnostics
   /// will be emitted and it is the responsibility of the caller to emit any
   /// that are needed.
   TypoExpr *CorrectTypoDelayed(
       const DeclarationNameInfo &Typo, Sema::LookupNameKind LookupKind,
       Scope *S, CXXScopeSpec *SS, CorrectionCandidateCallback &CCC,
       TypoDiagnosticGenerator TDG, TypoRecoveryCallback TRC,
       CorrectTypoKind Mode, DeclContext *MemberContext = nullptr,
       bool EnteringContext = false, const ObjCObjectPointerType *OPT = nullptr);
 
   /// Kinds of missing import. Note, the values of these enumerators correspond
   /// to %select values in diagnostics.
   enum class MissingImportKind {
     Declaration,
     Definition,
     DefaultArgument,
     ExplicitSpecialization,
     PartialSpecialization
   };
 
   /// Diagnose that the specified declaration needs to be visible but
   /// isn't, and suggest a module import that would resolve the problem.
   void diagnoseMissingImport(SourceLocation Loc, const NamedDecl *Decl,
                              MissingImportKind MIK, bool Recover = true);
   void diagnoseMissingImport(SourceLocation Loc, const NamedDecl *Decl,
                              SourceLocation DeclLoc, ArrayRef<Module *> Modules,
                              MissingImportKind MIK, bool Recover);
 
   struct TypoExprState {
     std::unique_ptr<TypoCorrectionConsumer> Consumer;
     TypoDiagnosticGenerator DiagHandler;
     TypoRecoveryCallback RecoveryHandler;
     TypoExprState();
     TypoExprState(TypoExprState &&other) noexcept;
     TypoExprState &operator=(TypoExprState &&other) noexcept;
   };
 
   const TypoExprState &getTypoExprState(TypoExpr *TE) const;
 
   /// Clears the state of the given TypoExpr.
   void clearDelayedTypo(TypoExpr *TE);
 
   /// Called on #pragma clang __debug dump II
   void ActOnPragmaDump(Scope *S, SourceLocation Loc, IdentifierInfo *II);
 
   /// Called on #pragma clang __debug dump E
   void ActOnPragmaDump(Expr *E);
 
 private:
   // The set of known/encountered (unique, canonicalized) NamespaceDecls.
   //
   // The boolean value will be true to indicate that the namespace was loaded
   // from an AST/PCH file, or false otherwise.
   llvm::MapVector<NamespaceDecl *, bool> KnownNamespaces;
 
   /// Whether we have already loaded known namespaces from an extenal
   /// source.
   bool LoadedExternalKnownNamespaces;
 
   bool CppLookupName(LookupResult &R, Scope *S);
 
   /// Determine if we could use all the declarations in the module.
   bool isUsableModule(const Module *M);
 
   /// Helper for CorrectTypo and CorrectTypoDelayed used to create and
   /// populate a new TypoCorrectionConsumer. Returns nullptr if typo correction
   /// should be skipped entirely.
   std::unique_ptr<TypoCorrectionConsumer> makeTypoCorrectionConsumer(
       const DeclarationNameInfo &Typo, Sema::LookupNameKind LookupKind,
       Scope *S, CXXScopeSpec *SS, CorrectionCandidateCallback &CCC,
       DeclContext *MemberContext, bool EnteringContext,
       const ObjCObjectPointerType *OPT, bool ErrorRecovery);
 
   /// The set of unhandled TypoExprs and their associated state.
   llvm::MapVector<TypoExpr *, TypoExprState> DelayedTypos;
 
   /// Creates a new TypoExpr AST node.
   TypoExpr *createDelayedTypo(std::unique_ptr<TypoCorrectionConsumer> TCC,
                               TypoDiagnosticGenerator TDG,
                               TypoRecoveryCallback TRC, SourceLocation TypoLoc);
 
   /// Cache for module units which is usable for current module.
   llvm::DenseSet<const Module *> UsableModuleUnitsCache;
 
   /// Record the typo correction failure and return an empty correction.
   TypoCorrection FailedCorrection(IdentifierInfo *Typo, SourceLocation TypoLoc,
                                   bool RecordFailure = true) {
     if (RecordFailure)
       TypoCorrectionFailures[Typo].insert(TypoLoc);
     return TypoCorrection();
   }
 
   bool isAcceptableSlow(const NamedDecl *D, AcceptableKind Kind);
 
   /// Determine whether two declarations should be linked together, given that
   /// the old declaration might not be visible and the new declaration might
   /// not have external linkage.
   bool shouldLinkPossiblyHiddenDecl(const NamedDecl *Old,
                                     const NamedDecl *New) {
     if (isVisible(Old))
       return true;
     // See comment in below overload for why it's safe to compute the linkage
     // of the new declaration here.
     if (New->isExternallyDeclarable()) {
       assert(Old->isExternallyDeclarable() &&
              "should not have found a non-externally-declarable previous decl");
       return true;
     }
     return false;
   }
   bool shouldLinkPossiblyHiddenDecl(LookupResult &Old, const NamedDecl *New);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Modules
   /// Implementations are in SemaModule.cpp
   ///@{
 
 public:
   /// Get the module unit whose scope we are currently within.
   Module *getCurrentModule() const {
     return ModuleScopes.empty() ? nullptr : ModuleScopes.back().Module;
   }
 
   /// Is the module scope we are an implementation unit?
   bool currentModuleIsImplementation() const {
     return ModuleScopes.empty()
                ? false
                : ModuleScopes.back().Module->isModuleImplementation();
   }
 
   // When loading a non-modular PCH files, this is used to restore module
   // visibility.
   void makeModuleVisible(Module *Mod, SourceLocation ImportLoc) {
     VisibleModules.setVisible(Mod, ImportLoc);
   }
 
   enum class ModuleDeclKind {
     Interface,               ///< 'export module X;'
     Implementation,          ///< 'module X;'
     PartitionInterface,      ///< 'export module X:Y;'
     PartitionImplementation, ///< 'module X:Y;'
   };
 
   /// An enumeration to represent the transition of states in parsing module
   /// fragments and imports.  If we are not parsing a C++20 TU, or we find
   /// an error in state transition, the state is set to NotACXX20Module.
   enum class ModuleImportState {
     FirstDecl,      ///< Parsing the first decl in a TU.
     GlobalFragment, ///< after 'module;' but before 'module X;'
     ImportAllowed,  ///< after 'module X;' but before any non-import decl.
     ImportFinished, ///< after any non-import decl.
     PrivateFragmentImportAllowed,  ///< after 'module :private;' but before any
                                    ///< non-import decl.
     PrivateFragmentImportFinished, ///< after 'module :private;' but a
                                    ///< non-import decl has already been seen.
     NotACXX20Module ///< Not a C++20 TU, or an invalid state was found.
   };
 
   /// The parser has processed a module-declaration that begins the definition
   /// of a module interface or implementation.
   DeclGroupPtrTy ActOnModuleDecl(SourceLocation StartLoc,
                                  SourceLocation ModuleLoc, ModuleDeclKind MDK,
                                  ModuleIdPath Path, ModuleIdPath Partition,
                                  ModuleImportState &ImportState);
 
   /// The parser has processed a global-module-fragment declaration that begins
   /// the definition of the global module fragment of the current module unit.
   /// \param ModuleLoc The location of the 'module' keyword.
   DeclGroupPtrTy ActOnGlobalModuleFragmentDecl(SourceLocation ModuleLoc);
 
   /// The parser has processed a private-module-fragment declaration that begins
   /// the definition of the private module fragment of the current module unit.
   /// \param ModuleLoc The location of the 'module' keyword.
   /// \param PrivateLoc The location of the 'private' keyword.
   DeclGroupPtrTy ActOnPrivateModuleFragmentDecl(SourceLocation ModuleLoc,
                                                 SourceLocation PrivateLoc);
 
   /// The parser has processed a module import declaration.
   ///
   /// \param StartLoc The location of the first token in the declaration. This
   ///        could be the location of an '@', 'export', or 'import'.
   /// \param ExportLoc The location of the 'export' keyword, if any.
   /// \param ImportLoc The location of the 'import' keyword.
   /// \param Path The module toplevel name as an access path.
   /// \param IsPartition If the name is for a partition.
   DeclResult ActOnModuleImport(SourceLocation StartLoc,
                                SourceLocation ExportLoc,
                                SourceLocation ImportLoc, ModuleIdPath Path,
                                bool IsPartition = false);
   DeclResult ActOnModuleImport(SourceLocation StartLoc,
                                SourceLocation ExportLoc,
                                SourceLocation ImportLoc, Module *M,
                                ModuleIdPath Path = {});
 
   /// The parser has processed a module import translated from a
   /// #include or similar preprocessing directive.
   void ActOnAnnotModuleInclude(SourceLocation DirectiveLoc, Module *Mod);
   void BuildModuleInclude(SourceLocation DirectiveLoc, Module *Mod);
 
   /// The parsed has entered a submodule.
   void ActOnAnnotModuleBegin(SourceLocation DirectiveLoc, Module *Mod);
   /// The parser has left a submodule.
   void ActOnAnnotModuleEnd(SourceLocation DirectiveLoc, Module *Mod);
 
   /// Create an implicit import of the given module at the given
   /// source location, for error recovery, if possible.
   ///
   /// This routine is typically used when an entity found by name lookup
   /// is actually hidden within a module that we know about but the user
   /// has forgotten to import.
   void createImplicitModuleImportForErrorRecovery(SourceLocation Loc,
                                                   Module *Mod);
 
   /// We have parsed the start of an export declaration, including the '{'
   /// (if present).
   Decl *ActOnStartExportDecl(Scope *S, SourceLocation ExportLoc,
                              SourceLocation LBraceLoc);
 
   /// Complete the definition of an export declaration.
   Decl *ActOnFinishExportDecl(Scope *S, Decl *ExportDecl,
                               SourceLocation RBraceLoc);
 
 private:
   /// The parser has begun a translation unit to be compiled as a C++20
   /// Header Unit, helper for ActOnStartOfTranslationUnit() only.
   void HandleStartOfHeaderUnit();
 
   struct ModuleScope {
     SourceLocation BeginLoc;
     clang::Module *Module = nullptr;
     VisibleModuleSet OuterVisibleModules;
   };
   /// The modules we're currently parsing.
   llvm::SmallVector<ModuleScope, 16> ModuleScopes;
 
   /// For an interface unit, this is the implicitly imported interface unit.
   clang::Module *ThePrimaryInterface = nullptr;
 
   /// The explicit global module fragment of the current translation unit.
   /// The explicit Global Module Fragment, as specified in C++
   /// [module.global.frag].
   clang::Module *TheGlobalModuleFragment = nullptr;
 
   /// The implicit global module fragments of the current translation unit.
   ///
   /// The contents in the implicit global module fragment can't be discarded.
   clang::Module *TheImplicitGlobalModuleFragment = nullptr;
 
   /// Namespace definitions that we will export when they finish.
   llvm::SmallPtrSet<const NamespaceDecl *, 8> DeferredExportedNamespaces;
 
   /// In a C++ standard module, inline declarations require a definition to be
   /// present at the end of a definition domain.  This set holds the decls to
   /// be checked at the end of the TU.
   llvm::SmallPtrSet<const FunctionDecl *, 8> PendingInlineFuncDecls;
 
   /// Helper function to judge if we are in module purview.
   /// Return false if we are not in a module.
   bool isCurrentModulePurview() const;
 
   /// Enter the scope of the explicit global module fragment.
   Module *PushGlobalModuleFragment(SourceLocation BeginLoc);
   /// Leave the scope of the explicit global module fragment.
   void PopGlobalModuleFragment();
 
   /// Enter the scope of an implicit global module fragment.
   Module *PushImplicitGlobalModuleFragment(SourceLocation BeginLoc);
   /// Leave the scope of an implicit global module fragment.
   void PopImplicitGlobalModuleFragment();
 
   VisibleModuleSet VisibleModules;
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Overloading
   /// Implementations are in SemaOverload.cpp
   ///@{
 
 public:
   /// Whether deferrable diagnostics should be deferred.
   bool DeferDiags = false;
 
   /// RAII class to control scope of DeferDiags.
   class DeferDiagsRAII {
     Sema &S;
     bool SavedDeferDiags = false;
 
   public:
     DeferDiagsRAII(Sema &S, bool DeferDiags)
         : S(S), SavedDeferDiags(S.DeferDiags) {
       S.DeferDiags = DeferDiags;
     }
     ~DeferDiagsRAII() { S.DeferDiags = SavedDeferDiags; }
   };
 
   /// Flag indicating if Sema is building a recovery call expression.
   ///
   /// This flag is used to avoid building recovery call expressions
   /// if Sema is already doing so, which would cause infinite recursions.
   bool IsBuildingRecoveryCallExpr;
 
   enum OverloadKind {
     /// This is a legitimate overload: the existing declarations are
     /// functions or function templates with different signatures.
     Ovl_Overload,
 
     /// This is not an overload because the signature exactly matches
     /// an existing declaration.
     Ovl_Match,
 
     /// This is not an overload because the lookup results contain a
     /// non-function.
     Ovl_NonFunction
   };
 
   /// Determine whether the given New declaration is an overload of the
   /// declarations in Old. This routine returns Ovl_Match or Ovl_NonFunction if
   /// New and Old cannot be overloaded, e.g., if New has the same signature as
   /// some function in Old (C++ 1.3.10) or if the Old declarations aren't
   /// functions (or function templates) at all. When it does return Ovl_Match or
   /// Ovl_NonFunction, MatchedDecl will point to the decl that New cannot be
   /// overloaded with. This decl may be a UsingShadowDecl on top of the
   /// underlying declaration.
   ///
   /// Example: Given the following input:
   ///
   ///   void f(int, float); // #1
   ///   void f(int, int); // #2
   ///   int f(int, int); // #3
   ///
   /// When we process #1, there is no previous declaration of "f", so IsOverload
   /// will not be used.
   ///
   /// When we process #2, Old contains only the FunctionDecl for #1. By
   /// comparing the parameter types, we see that #1 and #2 are overloaded (since
   /// they have different signatures), so this routine returns Ovl_Overload;
   /// MatchedDecl is unchanged.
   ///
   /// When we process #3, Old is an overload set containing #1 and #2. We
   /// compare the signatures of #3 to #1 (they're overloaded, so we do nothing)
   /// and then #3 to #2. Since the signatures of #3 and #2 are identical (return
   /// types of functions are not part of the signature), IsOverload returns
   /// Ovl_Match and MatchedDecl will be set to point to the FunctionDecl for #2.
   ///
   /// 'NewIsUsingShadowDecl' indicates that 'New' is being introduced into a
   /// class by a using declaration. The rules for whether to hide shadow
   /// declarations ignore some properties which otherwise figure into a function
   /// template's signature.
   OverloadKind CheckOverload(Scope *S, FunctionDecl *New,
                              const LookupResult &OldDecls, NamedDecl *&OldDecl,
                              bool UseMemberUsingDeclRules);
   bool IsOverload(FunctionDecl *New, FunctionDecl *Old,
                   bool UseMemberUsingDeclRules, bool ConsiderCudaAttrs = true);
 
   // Checks whether MD constitutes an override the base class method BaseMD.
   // When checking for overrides, the object object members are ignored.
   bool IsOverride(FunctionDecl *MD, FunctionDecl *BaseMD,
                   bool UseMemberUsingDeclRules, bool ConsiderCudaAttrs = true);
 
   enum class AllowedExplicit {
     /// Allow no explicit functions to be used.
     None,
     /// Allow explicit conversion functions but not explicit constructors.
     Conversions,
     /// Allow both explicit conversion functions and explicit constructors.
     All
   };
 
   ImplicitConversionSequence TryImplicitConversion(
       Expr *From, QualType ToType, bool SuppressUserConversions,
       AllowedExplicit AllowExplicit, bool InOverloadResolution, bool CStyle,
       bool AllowObjCWritebackConversion);
 
   /// PerformImplicitConversion - Perform an implicit conversion of the
   /// expression From to the type ToType. Returns the
   /// converted expression. Flavor is the kind of conversion we're
   /// performing, used in the error message. If @p AllowExplicit,
   /// explicit user-defined conversions are permitted.
   ExprResult PerformImplicitConversion(Expr *From, QualType ToType,
                                        AssignmentAction Action,
                                        bool AllowExplicit = false);
 
   /// IsIntegralPromotion - Determines whether the conversion from the
   /// expression From (whose potentially-adjusted type is FromType) to
   /// ToType is an integral promotion (C++ 4.5). If so, returns true and
   /// sets PromotedType to the promoted type.
   bool IsIntegralPromotion(Expr *From, QualType FromType, QualType ToType);
 
   /// IsFloatingPointPromotion - Determines whether the conversion from
   /// FromType to ToType is a floating point promotion (C++ 4.6). If so,
   /// returns true and sets PromotedType to the promoted type.
   bool IsFloatingPointPromotion(QualType FromType, QualType ToType);
 
   /// Determine if a conversion is a complex promotion.
   ///
   /// A complex promotion is defined as a complex -> complex conversion
   /// where the conversion between the underlying real types is a
   /// floating-point or integral promotion.
   bool IsComplexPromotion(QualType FromType, QualType ToType);
 
   /// IsPointerConversion - Determines whether the conversion of the
   /// expression From, which has the (possibly adjusted) type FromType,
   /// can be converted to the type ToType via a pointer conversion (C++
   /// 4.10). If so, returns true and places the converted type (that
   /// might differ from ToType in its cv-qualifiers at some level) into
   /// ConvertedType.
   ///
   /// This routine also supports conversions to and from block pointers
   /// and conversions with Objective-C's 'id', 'id<protocols...>', and
   /// pointers to interfaces. FIXME: Once we've determined the
   /// appropriate overloading rules for Objective-C, we may want to
   /// split the Objective-C checks into a different routine; however,
   /// GCC seems to consider all of these conversions to be pointer
   /// conversions, so for now they live here. IncompatibleObjC will be
   /// set if the conversion is an allowed Objective-C conversion that
   /// should result in a warning.
   bool IsPointerConversion(Expr *From, QualType FromType, QualType ToType,
                            bool InOverloadResolution, QualType &ConvertedType,
                            bool &IncompatibleObjC);
 
   /// isObjCPointerConversion - Determines whether this is an
   /// Objective-C pointer conversion. Subroutine of IsPointerConversion,
   /// with the same arguments and return values.
   bool isObjCPointerConversion(QualType FromType, QualType ToType,
                                QualType &ConvertedType, bool &IncompatibleObjC);
   bool IsBlockPointerConversion(QualType FromType, QualType ToType,
                                 QualType &ConvertedType);
 
   /// FunctionParamTypesAreEqual - This routine checks two function proto types
   /// for equality of their parameter types. Caller has already checked that
   /// they have same number of parameters.  If the parameters are different,
   /// ArgPos will have the parameter index of the first different parameter.
   /// If `Reversed` is true, the parameters of `NewType` will be compared in
   /// reverse order. That's useful if one of the functions is being used as a
   /// C++20 synthesized operator overload with a reversed parameter order.
   bool FunctionParamTypesAreEqual(ArrayRef<QualType> Old,
                                   ArrayRef<QualType> New,
                                   unsigned *ArgPos = nullptr,
                                   bool Reversed = false);
 
   bool FunctionParamTypesAreEqual(const FunctionProtoType *OldType,
                                   const FunctionProtoType *NewType,
                                   unsigned *ArgPos = nullptr,
                                   bool Reversed = false);
 
   bool FunctionNonObjectParamTypesAreEqual(const FunctionDecl *OldFunction,
                                            const FunctionDecl *NewFunction,
                                            unsigned *ArgPos = nullptr,
                                            bool Reversed = false);
 
   /// HandleFunctionTypeMismatch - Gives diagnostic information for differeing
   /// function types.  Catches different number of parameter, mismatch in
   /// parameter types, and different return types.
   void HandleFunctionTypeMismatch(PartialDiagnostic &PDiag, QualType FromType,
                                   QualType ToType);
 
   /// CheckPointerConversion - Check the pointer conversion from the
   /// expression From to the type ToType. This routine checks for
   /// ambiguous or inaccessible derived-to-base pointer
   /// conversions for which IsPointerConversion has already returned
   /// true. It returns true and produces a diagnostic if there was an
   /// error, or returns false otherwise.
   bool CheckPointerConversion(Expr *From, QualType ToType, CastKind &Kind,
                               CXXCastPath &BasePath, bool IgnoreBaseAccess,
                               bool Diagnose = true);
 
   /// IsMemberPointerConversion - Determines whether the conversion of the
   /// expression From, which has the (possibly adjusted) type FromType, can be
   /// converted to the type ToType via a member pointer conversion (C++ 4.11).
   /// If so, returns true and places the converted type (that might differ from
   /// ToType in its cv-qualifiers at some level) into ConvertedType.
   bool IsMemberPointerConversion(Expr *From, QualType FromType, QualType ToType,
                                  bool InOverloadResolution,
                                  QualType &ConvertedType);
 
   /// CheckMemberPointerConversion - Check the member pointer conversion from
   /// the expression From to the type ToType. This routine checks for ambiguous
   /// or virtual or inaccessible base-to-derived member pointer conversions for
   /// which IsMemberPointerConversion has already returned true. It returns true
   /// and produces a diagnostic if there was an error, or returns false
   /// otherwise.
   bool CheckMemberPointerConversion(Expr *From, QualType ToType, CastKind &Kind,
                                     CXXCastPath &BasePath,
                                     bool IgnoreBaseAccess);
 
   /// IsQualificationConversion - Determines whether the conversion from
   /// an rvalue of type FromType to ToType is a qualification conversion
   /// (C++ 4.4).
   ///
   /// \param ObjCLifetimeConversion Output parameter that will be set to
   /// indicate when the qualification conversion involves a change in the
   /// Objective-C object lifetime.
   bool IsQualificationConversion(QualType FromType, QualType ToType,
                                  bool CStyle, bool &ObjCLifetimeConversion);
 
   /// Determine whether the conversion from FromType to ToType is a valid
   /// conversion that strips "noexcept" or "noreturn" off the nested function
   /// type.
   bool IsFunctionConversion(QualType FromType, QualType ToType,
                             QualType &ResultTy);
   bool DiagnoseMultipleUserDefinedConversion(Expr *From, QualType ToType);
   void DiagnoseUseOfDeletedFunction(SourceLocation Loc, SourceRange Range,
                                     DeclarationName Name,
                                     OverloadCandidateSet &CandidateSet,
                                     FunctionDecl *Fn, MultiExprArg Args,
                                     bool IsMember = false);
 
   ExprResult InitializeExplicitObjectArgument(Sema &S, Expr *Obj,
                                               FunctionDecl *Fun);
   ExprResult PerformImplicitObjectArgumentInitialization(
       Expr *From, NestedNameSpecifier *Qualifier, NamedDecl *FoundDecl,
       CXXMethodDecl *Method);
 
   /// PerformContextuallyConvertToBool - Perform a contextual conversion
   /// of the expression From to bool (C++0x [conv]p3).
   ExprResult PerformContextuallyConvertToBool(Expr *From);
 
   /// PerformContextuallyConvertToObjCPointer - Perform a contextual
   /// conversion of the expression From to an Objective-C pointer type.
   /// Returns a valid but null ExprResult if no conversion sequence exists.
   ExprResult PerformContextuallyConvertToObjCPointer(Expr *From);
 
   /// Contexts in which a converted constant expression is required.
   enum CCEKind {
     CCEK_CaseValue,    ///< Expression in a case label.
     CCEK_Enumerator,   ///< Enumerator value with fixed underlying type.
     CCEK_TemplateArg,  ///< Value of a non-type template parameter.
     CCEK_InjectedTTP,  ///< Injected parameter of a template template parameter.
     CCEK_ArrayBound,   ///< Array bound in array declarator or new-expression.
     CCEK_ExplicitBool, ///< Condition in an explicit(bool) specifier.
     CCEK_Noexcept,     ///< Condition in a noexcept(bool) specifier.
     CCEK_StaticAssertMessageSize, ///< Call to size() in a static assert
                                   ///< message.
     CCEK_StaticAssertMessageData, ///< Call to data() in a static assert
                                   ///< message.
   };
 
   ExprResult BuildConvertedConstantExpression(Expr *From, QualType T,
                                               CCEKind CCE,
                                               NamedDecl *Dest = nullptr);
 
   ExprResult CheckConvertedConstantExpression(Expr *From, QualType T,
                                               llvm::APSInt &Value, CCEKind CCE);
   ExprResult CheckConvertedConstantExpression(Expr *From, QualType T,
                                               APValue &Value, CCEKind CCE,
                                               NamedDecl *Dest = nullptr);
 
   /// EvaluateConvertedConstantExpression - Evaluate an Expression
   /// That is a converted constant expression
   /// (which was built with BuildConvertedConstantExpression)
   ExprResult
   EvaluateConvertedConstantExpression(Expr *E, QualType T, APValue &Value,
                                       CCEKind CCE, bool RequireInt,
                                       const APValue &PreNarrowingValue);
 
   /// Abstract base class used to perform a contextual implicit
   /// conversion from an expression to any type passing a filter.
   class ContextualImplicitConverter {
   public:
     bool Suppress;
     bool SuppressConversion;
 
     ContextualImplicitConverter(bool Suppress = false,
                                 bool SuppressConversion = false)
         : Suppress(Suppress), SuppressConversion(SuppressConversion) {}
 
     /// Determine whether the specified type is a valid destination type
     /// for this conversion.
     virtual bool match(QualType T) = 0;
 
     /// Emits a diagnostic complaining that the expression does not have
     /// integral or enumeration type.
     virtual SemaDiagnosticBuilder diagnoseNoMatch(Sema &S, SourceLocation Loc,
                                                   QualType T) = 0;
 
     /// Emits a diagnostic when the expression has incomplete class type.
     virtual SemaDiagnosticBuilder
     diagnoseIncomplete(Sema &S, SourceLocation Loc, QualType T) = 0;
 
     /// Emits a diagnostic when the only matching conversion function
     /// is explicit.
     virtual SemaDiagnosticBuilder diagnoseExplicitConv(Sema &S,
                                                        SourceLocation Loc,
                                                        QualType T,
                                                        QualType ConvTy) = 0;
 
     /// Emits a note for the explicit conversion function.
     virtual SemaDiagnosticBuilder
     noteExplicitConv(Sema &S, CXXConversionDecl *Conv, QualType ConvTy) = 0;
 
     /// Emits a diagnostic when there are multiple possible conversion
     /// functions.
     virtual SemaDiagnosticBuilder diagnoseAmbiguous(Sema &S, SourceLocation Loc,
                                                     QualType T) = 0;
 
     /// Emits a note for one of the candidate conversions.
     virtual SemaDiagnosticBuilder
     noteAmbiguous(Sema &S, CXXConversionDecl *Conv, QualType ConvTy) = 0;
 
     /// Emits a diagnostic when we picked a conversion function
     /// (for cases when we are not allowed to pick a conversion function).
     virtual SemaDiagnosticBuilder diagnoseConversion(Sema &S,
                                                      SourceLocation Loc,
                                                      QualType T,
                                                      QualType ConvTy) = 0;
 
     virtual ~ContextualImplicitConverter() {}
   };
 
   class ICEConvertDiagnoser : public ContextualImplicitConverter {
     bool AllowScopedEnumerations;
 
   public:
     ICEConvertDiagnoser(bool AllowScopedEnumerations, bool Suppress,
                         bool SuppressConversion)
         : ContextualImplicitConverter(Suppress, SuppressConversion),
           AllowScopedEnumerations(AllowScopedEnumerations) {}
 
     /// Match an integral or (possibly scoped) enumeration type.
     bool match(QualType T) override;
 
     SemaDiagnosticBuilder diagnoseNoMatch(Sema &S, SourceLocation Loc,
                                           QualType T) override {
       return diagnoseNotInt(S, Loc, T);
     }
 
     /// Emits a diagnostic complaining that the expression does not have
     /// integral or enumeration type.
     virtual SemaDiagnosticBuilder diagnoseNotInt(Sema &S, SourceLocation Loc,
                                                  QualType T) = 0;
   };
 
   /// Perform a contextual implicit conversion.
   ExprResult
   PerformContextualImplicitConversion(SourceLocation Loc, Expr *FromE,
                                       ContextualImplicitConverter &Converter);
 
   /// ReferenceCompareResult - Expresses the result of comparing two
   /// types (cv1 T1 and cv2 T2) to determine their compatibility for the
   /// purposes of initialization by reference (C++ [dcl.init.ref]p4).
   enum ReferenceCompareResult {
     /// Ref_Incompatible - The two types are incompatible, so direct
     /// reference binding is not possible.
     Ref_Incompatible = 0,
     /// Ref_Related - The two types are reference-related, which means
     /// that their unqualified forms (T1 and T2) are either the same
     /// or T1 is a base class of T2.
     Ref_Related,
     /// Ref_Compatible - The two types are reference-compatible.
     Ref_Compatible
   };
 
   // Fake up a scoped enumeration that still contextually converts to bool.
   struct ReferenceConversionsScope {
     /// The conversions that would be performed on an lvalue of type T2 when
     /// binding a reference of type T1 to it, as determined when evaluating
     /// whether T1 is reference-compatible with T2.
     enum ReferenceConversions {
       Qualification = 0x1,
       NestedQualification = 0x2,
       Function = 0x4,
       DerivedToBase = 0x8,
       ObjC = 0x10,
       ObjCLifetime = 0x20,
 
       LLVM_MARK_AS_BITMASK_ENUM(/*LargestValue=*/ObjCLifetime)
     };
   };
   using ReferenceConversions = ReferenceConversionsScope::ReferenceConversions;
 
   /// CompareReferenceRelationship - Compare the two types T1 and T2 to
   /// determine whether they are reference-compatible,
   /// reference-related, or incompatible, for use in C++ initialization by
   /// reference (C++ [dcl.ref.init]p4). Neither type can be a reference
   /// type, and the first type (T1) is the pointee type of the reference
   /// type being initialized.
   ReferenceCompareResult
   CompareReferenceRelationship(SourceLocation Loc, QualType T1, QualType T2,
                                ReferenceConversions *Conv = nullptr);
 
   /// AddOverloadCandidate - Adds the given function to the set of
   /// candidate functions, using the given function call arguments.  If
   /// @p SuppressUserConversions, then don't allow user-defined
   /// conversions via constructors or conversion operators.
   ///
   /// \param PartialOverloading true if we are performing "partial" overloading
   /// based on an incomplete set of function arguments. This feature is used by
   /// code completion.
   void AddOverloadCandidate(FunctionDecl *Function, DeclAccessPair FoundDecl,
                             ArrayRef<Expr *> Args,
                             OverloadCandidateSet &CandidateSet,
                             bool SuppressUserConversions = false,
                             bool PartialOverloading = false,
                             bool AllowExplicit = true,
                             bool AllowExplicitConversion = false,
                             ADLCallKind IsADLCandidate = ADLCallKind::NotADL,
                             ConversionSequenceList EarlyConversions = {},
                             OverloadCandidateParamOrder PO = {},
                             bool AggregateCandidateDeduction = false,
                             bool HasMatchedPackOnParmToNonPackOnArg = false);
 
   /// Add all of the function declarations in the given function set to
   /// the overload candidate set.
   void AddFunctionCandidates(
       const UnresolvedSetImpl &Functions, ArrayRef<Expr *> Args,
       OverloadCandidateSet &CandidateSet,
       TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr,
       bool SuppressUserConversions = false, bool PartialOverloading = false,
       bool FirstArgumentIsBase = false);
 
   /// AddMethodCandidate - Adds a named decl (which is some kind of
   /// method) as a method candidate to the given overload set.
   void AddMethodCandidate(DeclAccessPair FoundDecl, QualType ObjectType,
                           Expr::Classification ObjectClassification,
                           ArrayRef<Expr *> Args,
                           OverloadCandidateSet &CandidateSet,
                           bool SuppressUserConversion = false,
                           OverloadCandidateParamOrder PO = {});
 
   /// AddMethodCandidate - Adds the given C++ member function to the set
   /// of candidate functions, using the given function call arguments
   /// and the object argument (@c Object). For example, in a call
   /// @c o.f(a1,a2), @c Object will contain @c o and @c Args will contain
   /// both @c a1 and @c a2. If @p SuppressUserConversions, then don't
   /// allow user-defined conversions via constructors or conversion
   /// operators.
   void AddMethodCandidate(CXXMethodDecl *Method, DeclAccessPair FoundDecl,
                           CXXRecordDecl *ActingContext, QualType ObjectType,
                           Expr::Classification ObjectClassification,
                           ArrayRef<Expr *> Args,
                           OverloadCandidateSet &CandidateSet,
                           bool SuppressUserConversions = false,
                           bool PartialOverloading = false,
                           ConversionSequenceList EarlyConversions = {},
                           OverloadCandidateParamOrder PO = {},
                           bool HasMatchedPackOnParmToNonPackOnArg = false);
 
   /// Add a C++ member function template as a candidate to the candidate
   /// set, using template argument deduction to produce an appropriate member
   /// function template specialization.
   void AddMethodTemplateCandidate(
       FunctionTemplateDecl *MethodTmpl, DeclAccessPair FoundDecl,
       CXXRecordDecl *ActingContext,
       TemplateArgumentListInfo *ExplicitTemplateArgs, QualType ObjectType,
       Expr::Classification ObjectClassification, ArrayRef<Expr *> Args,
       OverloadCandidateSet &CandidateSet, bool SuppressUserConversions = false,
       bool PartialOverloading = false, OverloadCandidateParamOrder PO = {});
 
   /// Add a C++ function template specialization as a candidate
   /// in the candidate set, using template argument deduction to produce
   /// an appropriate function template specialization.
   void AddTemplateOverloadCandidate(
       FunctionTemplateDecl *FunctionTemplate, DeclAccessPair FoundDecl,
       TemplateArgumentListInfo *ExplicitTemplateArgs, ArrayRef<Expr *> Args,
       OverloadCandidateSet &CandidateSet, bool SuppressUserConversions = false,
       bool PartialOverloading = false, bool AllowExplicit = true,
       ADLCallKind IsADLCandidate = ADLCallKind::NotADL,
       OverloadCandidateParamOrder PO = {},
       bool AggregateCandidateDeduction = false);
 
   /// Check that implicit conversion sequences can be formed for each argument
   /// whose corresponding parameter has a non-dependent type, per DR1391's
   /// [temp.deduct.call]p10.
   bool CheckNonDependentConversions(
       FunctionTemplateDecl *FunctionTemplate, ArrayRef<QualType> ParamTypes,
       ArrayRef<Expr *> Args, OverloadCandidateSet &CandidateSet,
       ConversionSequenceList &Conversions, bool SuppressUserConversions,
       CXXRecordDecl *ActingContext = nullptr, QualType ObjectType = QualType(),
       Expr::Classification ObjectClassification = {},
       OverloadCandidateParamOrder PO = {});
 
   /// AddConversionCandidate - Add a C++ conversion function as a
   /// candidate in the candidate set (C++ [over.match.conv],
   /// C++ [over.match.copy]). From is the expression we're converting from,
   /// and ToType is the type that we're eventually trying to convert to
   /// (which may or may not be the same type as the type that the
   /// conversion function produces).
   void AddConversionCandidate(
       CXXConversionDecl *Conversion, DeclAccessPair FoundDecl,
       CXXRecordDecl *ActingContext, Expr *From, QualType ToType,
       OverloadCandidateSet &CandidateSet, bool AllowObjCConversionOnExplicit,
       bool AllowExplicit, bool AllowResultConversion = true,
       bool HasMatchedPackOnParmToNonPackOnArg = false);
 
   /// Adds a conversion function template specialization
   /// candidate to the overload set, using template argument deduction
   /// to deduce the template arguments of the conversion function
   /// template from the type that we are converting to (C++
   /// [temp.deduct.conv]).
   void AddTemplateConversionCandidate(
       FunctionTemplateDecl *FunctionTemplate, DeclAccessPair FoundDecl,
       CXXRecordDecl *ActingContext, Expr *From, QualType ToType,
       OverloadCandidateSet &CandidateSet, bool AllowObjCConversionOnExplicit,
       bool AllowExplicit, bool AllowResultConversion = true);
 
   /// AddSurrogateCandidate - Adds a "surrogate" candidate function that
   /// converts the given @c Object to a function pointer via the
   /// conversion function @c Conversion, and then attempts to call it
   /// with the given arguments (C++ [over.call.object]p2-4). Proto is
   /// the type of function that we'll eventually be calling.
   void AddSurrogateCandidate(CXXConversionDecl *Conversion,
                              DeclAccessPair FoundDecl,
                              CXXRecordDecl *ActingContext,
                              const FunctionProtoType *Proto, Expr *Object,
                              ArrayRef<Expr *> Args,
                              OverloadCandidateSet &CandidateSet);
 
   /// Add all of the non-member operator function declarations in the given
   /// function set to the overload candidate set.
   void AddNonMemberOperatorCandidates(
       const UnresolvedSetImpl &Functions, ArrayRef<Expr *> Args,
       OverloadCandidateSet &CandidateSet,
       TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr);
 
   /// Add overload candidates for overloaded operators that are
   /// member functions.
   ///
   /// Add the overloaded operator candidates that are member functions
   /// for the operator Op that was used in an operator expression such
   /// as "x Op y". , Args/NumArgs provides the operator arguments, and
   /// CandidateSet will store the added overload candidates. (C++
   /// [over.match.oper]).
   void AddMemberOperatorCandidates(OverloadedOperatorKind Op,
                                    SourceLocation OpLoc, ArrayRef<Expr *> Args,
                                    OverloadCandidateSet &CandidateSet,
                                    OverloadCandidateParamOrder PO = {});
 
   /// AddBuiltinCandidate - Add a candidate for a built-in
   /// operator. ResultTy and ParamTys are the result and parameter types
   /// of the built-in candidate, respectively. Args and NumArgs are the
   /// arguments being passed to the candidate. IsAssignmentOperator
   /// should be true when this built-in candidate is an assignment
   /// operator. NumContextualBoolArguments is the number of arguments
   /// (at the beginning of the argument list) that will be contextually
   /// converted to bool.
   void AddBuiltinCandidate(QualType *ParamTys, ArrayRef<Expr *> Args,
                            OverloadCandidateSet &CandidateSet,
                            bool IsAssignmentOperator = false,
                            unsigned NumContextualBoolArguments = 0);
 
   /// AddBuiltinOperatorCandidates - Add the appropriate built-in
   /// operator overloads to the candidate set (C++ [over.built]), based
   /// on the operator @p Op and the arguments given. For example, if the
   /// operator is a binary '+', this routine might add "int
   /// operator+(int, int)" to cover integer addition.
   void AddBuiltinOperatorCandidates(OverloadedOperatorKind Op,
                                     SourceLocation OpLoc, ArrayRef<Expr *> Args,
                                     OverloadCandidateSet &CandidateSet);
 
   /// Add function candidates found via argument-dependent lookup
   /// to the set of overloading candidates.
   ///
   /// This routine performs argument-dependent name lookup based on the
   /// given function name (which may also be an operator name) and adds
   /// all of the overload candidates found by ADL to the overload
   /// candidate set (C++ [basic.lookup.argdep]).
   void AddArgumentDependentLookupCandidates(
       DeclarationName Name, SourceLocation Loc, ArrayRef<Expr *> Args,
       TemplateArgumentListInfo *ExplicitTemplateArgs,
       OverloadCandidateSet &CandidateSet, bool PartialOverloading = false);
 
   /// Check the enable_if expressions on the given function. Returns the first
   /// failing attribute, or NULL if they were all successful.
   EnableIfAttr *CheckEnableIf(FunctionDecl *Function, SourceLocation CallLoc,
                               ArrayRef<Expr *> Args,
                               bool MissingImplicitThis = false);
 
   /// Emit diagnostics for the diagnose_if attributes on Function, ignoring any
   /// non-ArgDependent DiagnoseIfAttrs.
   ///
   /// Argument-dependent diagnose_if attributes should be checked each time a
   /// function is used as a direct callee of a function call.
   ///
   /// Returns true if any errors were emitted.
   bool diagnoseArgDependentDiagnoseIfAttrs(const FunctionDecl *Function,
                                            const Expr *ThisArg,
                                            ArrayRef<const Expr *> Args,
                                            SourceLocation Loc);
 
   /// Emit diagnostics for the diagnose_if attributes on Function, ignoring any
   /// ArgDependent DiagnoseIfAttrs.
   ///
   /// Argument-independent diagnose_if attributes should be checked on every use
   /// of a function.
   ///
   /// Returns true if any errors were emitted.
   bool diagnoseArgIndependentDiagnoseIfAttrs(const NamedDecl *ND,
                                              SourceLocation Loc);
 
   /// Determine if \p A and \p B are equivalent internal linkage declarations
   /// from different modules, and thus an ambiguity error can be downgraded to
   /// an extension warning.
   bool isEquivalentInternalLinkageDeclaration(const NamedDecl *A,
                                               const NamedDecl *B);
   void diagnoseEquivalentInternalLinkageDeclarations(
       SourceLocation Loc, const NamedDecl *D,
       ArrayRef<const NamedDecl *> Equiv);
 
   // Emit as a 'note' the specific overload candidate
   void NoteOverloadCandidate(
       const NamedDecl *Found, const FunctionDecl *Fn,
       OverloadCandidateRewriteKind RewriteKind = OverloadCandidateRewriteKind(),
       QualType DestType = QualType(), bool TakingAddress = false);
 
   // Emit as a series of 'note's all template and non-templates identified by
   // the expression Expr
   void NoteAllOverloadCandidates(Expr *E, QualType DestType = QualType(),
                                  bool TakingAddress = false);
 
   /// Returns whether the given function's address can be taken or not,
   /// optionally emitting a diagnostic if the address can't be taken.
   ///
   /// Returns false if taking the address of the function is illegal.
   bool checkAddressOfFunctionIsAvailable(const FunctionDecl *Function,
                                          bool Complain = false,
                                          SourceLocation Loc = SourceLocation());
 
   // [PossiblyAFunctionType]  -->   [Return]
   // NonFunctionType --> NonFunctionType
   // R (A) --> R(A)
   // R (*)(A) --> R (A)
   // R (&)(A) --> R (A)
   // R (S::*)(A) --> R (A)
   QualType ExtractUnqualifiedFunctionType(QualType PossiblyAFunctionType);
 
   /// ResolveAddressOfOverloadedFunction - Try to resolve the address of
   /// an overloaded function (C++ [over.over]), where @p From is an
   /// expression with overloaded function type and @p ToType is the type
   /// we're trying to resolve to. For example:
   ///
   /// @code
   /// int f(double);
   /// int f(int);
   ///
   /// int (*pfd)(double) = f; // selects f(double)
   /// @endcode
   ///
   /// This routine returns the resulting FunctionDecl if it could be
   /// resolved, and NULL otherwise. When @p Complain is true, this
   /// routine will emit diagnostics if there is an error.
   FunctionDecl *
   ResolveAddressOfOverloadedFunction(Expr *AddressOfExpr, QualType TargetType,
                                      bool Complain, DeclAccessPair &Found,
                                      bool *pHadMultipleCandidates = nullptr);
 
   /// Given an expression that refers to an overloaded function, try to
   /// resolve that function to a single function that can have its address
   /// taken. This will modify `Pair` iff it returns non-null.
   ///
   /// This routine can only succeed if from all of the candidates in the
   /// overload set for SrcExpr that can have their addresses taken, there is one
   /// candidate that is more constrained than the rest.
   FunctionDecl *
   resolveAddressOfSingleOverloadCandidate(Expr *E, DeclAccessPair &FoundResult);
 
   /// Given an overloaded function, tries to turn it into a non-overloaded
   /// function reference using resolveAddressOfSingleOverloadCandidate. This
   /// will perform access checks, diagnose the use of the resultant decl, and,
   /// if requested, potentially perform a function-to-pointer decay.
   ///
   /// Returns false if resolveAddressOfSingleOverloadCandidate fails.
   /// Otherwise, returns true. This may emit diagnostics and return true.
   bool resolveAndFixAddressOfSingleOverloadCandidate(
       ExprResult &SrcExpr, bool DoFunctionPointerConversion = false);
 
   /// Given an expression that refers to an overloaded function, try to
   /// resolve that overloaded function expression down to a single function.
   ///
   /// This routine can only resolve template-ids that refer to a single function
   /// template, where that template-id refers to a single template whose
   /// template arguments are either provided by the template-id or have
   /// defaults, as described in C++0x [temp.arg.explicit]p3.
   ///
   /// If no template-ids are found, no diagnostics are emitted and NULL is
   /// returned.
   FunctionDecl *ResolveSingleFunctionTemplateSpecialization(
       OverloadExpr *ovl, bool Complain = false, DeclAccessPair *Found = nullptr,
       TemplateSpecCandidateSet *FailedTSC = nullptr);
 
   // Resolve and fix an overloaded expression that can be resolved
   // because it identifies a single function template specialization.
   //
   // Last three arguments should only be supplied if Complain = true
   //
   // Return true if it was logically possible to so resolve the
   // expression, regardless of whether or not it succeeded.  Always
   // returns true if 'complain' is set.
   bool ResolveAndFixSingleFunctionTemplateSpecialization(
       ExprResult &SrcExpr, bool DoFunctionPointerConversion = false,
       bool Complain = false, SourceRange OpRangeForComplaining = SourceRange(),
       QualType DestTypeForComplaining = QualType(),
       unsigned DiagIDForComplaining = 0);
 
   /// Add the overload candidates named by callee and/or found by argument
   /// dependent lookup to the given overload set.
   void AddOverloadedCallCandidates(UnresolvedLookupExpr *ULE,
                                    ArrayRef<Expr *> Args,
                                    OverloadCandidateSet &CandidateSet,
                                    bool PartialOverloading = false);
 
   /// Add the call candidates from the given set of lookup results to the given
   /// overload set. Non-function lookup results are ignored.
   void AddOverloadedCallCandidates(
       LookupResult &R, TemplateArgumentListInfo *ExplicitTemplateArgs,
       ArrayRef<Expr *> Args, OverloadCandidateSet &CandidateSet);
 
   // An enum used to represent the different possible results of building a
   // range-based for loop.
   enum ForRangeStatus {
     FRS_Success,
     FRS_NoViableFunction,
     FRS_DiagnosticIssued
   };
 
   /// Build a call to 'begin' or 'end' for a C++11 for-range statement. If the
   /// given LookupResult is non-empty, it is assumed to describe a member which
   /// will be invoked. Otherwise, the function will be found via argument
   /// dependent lookup.
   /// CallExpr is set to a valid expression and FRS_Success returned on success,
   /// otherwise CallExpr is set to ExprError() and some non-success value
   /// is returned.
   ForRangeStatus BuildForRangeBeginEndCall(SourceLocation Loc,
                                            SourceLocation RangeLoc,
                                            const DeclarationNameInfo &NameInfo,
                                            LookupResult &MemberLookup,
                                            OverloadCandidateSet *CandidateSet,
                                            Expr *Range, ExprResult *CallExpr);
 
   /// BuildOverloadedCallExpr - Given the call expression that calls Fn
   /// (which eventually refers to the declaration Func) and the call
   /// arguments Args/NumArgs, attempt to resolve the function call down
   /// to a specific function. If overload resolution succeeds, returns
   /// the call expression produced by overload resolution.
   /// Otherwise, emits diagnostics and returns ExprError.
   ExprResult BuildOverloadedCallExpr(
       Scope *S, Expr *Fn, UnresolvedLookupExpr *ULE, SourceLocation LParenLoc,
       MultiExprArg Args, SourceLocation RParenLoc, Expr *ExecConfig,
       bool AllowTypoCorrection = true, bool CalleesAddressIsTaken = false);
 
   /// Constructs and populates an OverloadedCandidateSet from
   /// the given function.
   /// \returns true when an the ExprResult output parameter has been set.
   bool buildOverloadedCallSet(Scope *S, Expr *Fn, UnresolvedLookupExpr *ULE,
                               MultiExprArg Args, SourceLocation RParenLoc,
                               OverloadCandidateSet *CandidateSet,
                               ExprResult *Result);
 
   ExprResult CreateUnresolvedLookupExpr(CXXRecordDecl *NamingClass,
                                         NestedNameSpecifierLoc NNSLoc,
                                         DeclarationNameInfo DNI,
                                         const UnresolvedSetImpl &Fns,
                                         bool PerformADL = true);
 
   /// Create a unary operation that may resolve to an overloaded
   /// operator.
   ///
   /// \param OpLoc The location of the operator itself (e.g., '*').
   ///
   /// \param Opc The UnaryOperatorKind that describes this operator.
   ///
   /// \param Fns The set of non-member functions that will be
   /// considered by overload resolution. The caller needs to build this
   /// set based on the context using, e.g.,
   /// LookupOverloadedOperatorName() and ArgumentDependentLookup(). This
   /// set should not contain any member functions; those will be added
   /// by CreateOverloadedUnaryOp().
   ///
   /// \param Input The input argument.
   ExprResult CreateOverloadedUnaryOp(SourceLocation OpLoc,
                                      UnaryOperatorKind Opc,
                                      const UnresolvedSetImpl &Fns, Expr *input,
                                      bool RequiresADL = true);
 
   /// Perform lookup for an overloaded binary operator.
   void LookupOverloadedBinOp(OverloadCandidateSet &CandidateSet,
                              OverloadedOperatorKind Op,
                              const UnresolvedSetImpl &Fns,
                              ArrayRef<Expr *> Args, bool RequiresADL = true);
 
   /// Create a binary operation that may resolve to an overloaded
   /// operator.
   ///
   /// \param OpLoc The location of the operator itself (e.g., '+').
   ///
   /// \param Opc The BinaryOperatorKind that describes this operator.
   ///
   /// \param Fns The set of non-member functions that will be
   /// considered by overload resolution. The caller needs to build this
   /// set based on the context using, e.g.,
   /// LookupOverloadedOperatorName() and ArgumentDependentLookup(). This
   /// set should not contain any member functions; those will be added
   /// by CreateOverloadedBinOp().
   ///
   /// \param LHS Left-hand argument.
   /// \param RHS Right-hand argument.
   /// \param PerformADL Whether to consider operator candidates found by ADL.
   /// \param AllowRewrittenCandidates Whether to consider candidates found by
   ///        C++20 operator rewrites.
   /// \param DefaultedFn If we are synthesizing a defaulted operator function,
   ///        the function in question. Such a function is never a candidate in
   ///        our overload resolution. This also enables synthesizing a three-way
   ///        comparison from < and == as described in C++20 [class.spaceship]p1.
   ExprResult CreateOverloadedBinOp(SourceLocation OpLoc, BinaryOperatorKind Opc,
                                    const UnresolvedSetImpl &Fns, Expr *LHS,
                                    Expr *RHS, bool RequiresADL = true,
                                    bool AllowRewrittenCandidates = true,
                                    FunctionDecl *DefaultedFn = nullptr);
   ExprResult BuildSynthesizedThreeWayComparison(SourceLocation OpLoc,
                                                 const UnresolvedSetImpl &Fns,
                                                 Expr *LHS, Expr *RHS,
                                                 FunctionDecl *DefaultedFn);
 
   ExprResult CreateOverloadedArraySubscriptExpr(SourceLocation LLoc,
                                                 SourceLocation RLoc, Expr *Base,
                                                 MultiExprArg Args);
 
   /// BuildCallToMemberFunction - Build a call to a member
   /// function. MemExpr is the expression that refers to the member
   /// function (and includes the object parameter), Args/NumArgs are the
   /// arguments to the function call (not including the object
   /// parameter). The caller needs to validate that the member
   /// expression refers to a non-static member function or an overloaded
   /// member function.
   ExprResult BuildCallToMemberFunction(
       Scope *S, Expr *MemExpr, SourceLocation LParenLoc, MultiExprArg Args,
       SourceLocation RParenLoc, Expr *ExecConfig = nullptr,
       bool IsExecConfig = false, bool AllowRecovery = false);
 
   /// BuildCallToObjectOfClassType - Build a call to an object of class
   /// type (C++ [over.call.object]), which can end up invoking an
   /// overloaded function call operator (@c operator()) or performing a
   /// user-defined conversion on the object argument.
   ExprResult BuildCallToObjectOfClassType(Scope *S, Expr *Object,
                                           SourceLocation LParenLoc,
                                           MultiExprArg Args,
                                           SourceLocation RParenLoc);
 
   /// BuildOverloadedArrowExpr - Build a call to an overloaded @c operator->
   ///  (if one exists), where @c Base is an expression of class type and
   /// @c Member is the name of the member we're trying to find.
   ExprResult BuildOverloadedArrowExpr(Scope *S, Expr *Base,
                                       SourceLocation OpLoc,
                                       bool *NoArrowOperatorFound = nullptr);
 
   ExprResult BuildCXXMemberCallExpr(Expr *Exp, NamedDecl *FoundDecl,
                                     CXXConversionDecl *Method,
                                     bool HadMultipleCandidates);
 
   /// BuildLiteralOperatorCall - Build a UserDefinedLiteral by creating a call
   /// to a literal operator described by the provided lookup results.
   ExprResult BuildLiteralOperatorCall(
       LookupResult &R, DeclarationNameInfo &SuffixInfo, ArrayRef<Expr *> Args,
       SourceLocation LitEndLoc,
       TemplateArgumentListInfo *ExplicitTemplateArgs = nullptr);
 
   /// FixOverloadedFunctionReference - E is an expression that refers to
   /// a C++ overloaded function (possibly with some parentheses and
   /// perhaps a '&' around it). We have resolved the overloaded function
   /// to the function declaration Fn, so patch up the expression E to
   /// refer (possibly indirectly) to Fn. Returns the new expr.
   ExprResult FixOverloadedFunctionReference(Expr *E, DeclAccessPair FoundDecl,
                                             FunctionDecl *Fn);
   ExprResult FixOverloadedFunctionReference(ExprResult,
                                             DeclAccessPair FoundDecl,
                                             FunctionDecl *Fn);
 
   /// - Returns a selector which best matches given argument list or
   /// nullptr if none could be found
   ObjCMethodDecl *SelectBestMethod(Selector Sel, MultiExprArg Args,
                                    bool IsInstance,
                                    SmallVectorImpl<ObjCMethodDecl *> &Methods);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Statements
   /// Implementations are in SemaStmt.cpp
   ///@{
 
 public:
   /// Stack of active SEH __finally scopes.  Can be empty.
   SmallVector<Scope *, 2> CurrentSEHFinally;
 
   StmtResult ActOnExprStmt(ExprResult Arg, bool DiscardedValue = true);
   StmtResult ActOnExprStmtError();
 
   StmtResult ActOnNullStmt(SourceLocation SemiLoc,
                            bool HasLeadingEmptyMacro = false);
 
   StmtResult ActOnDeclStmt(DeclGroupPtrTy Decl, SourceLocation StartLoc,
                            SourceLocation EndLoc);
   void ActOnForEachDeclStmt(DeclGroupPtrTy Decl);
 
 
   // Unused, kept in Clang 20 for ABI stability.
   void DiagnoseDiscardedExprMarkedNodiscard(const Expr *E);
 
   /// DiagnoseUnusedExprResult - If the statement passed in is an expression
   /// whose result is unused, warn.
   void DiagnoseUnusedExprResult(const Stmt *S, unsigned DiagID);
 
   void ActOnStartOfCompoundStmt(bool IsStmtExpr);
   void ActOnAfterCompoundStatementLeadingPragmas();
   void ActOnFinishOfCompoundStmt();
   StmtResult ActOnCompoundStmt(SourceLocation L, SourceLocation R,
                                ArrayRef<Stmt *> Elts, bool isStmtExpr);
 
   sema::CompoundScopeInfo &getCurCompoundScope() const;
 
   ExprResult ActOnCaseExpr(SourceLocation CaseLoc, ExprResult Val);
   StmtResult ActOnCaseStmt(SourceLocation CaseLoc, ExprResult LHS,
                            SourceLocation DotDotDotLoc, ExprResult RHS,
                            SourceLocation ColonLoc);
 
   /// ActOnCaseStmtBody - This installs a statement as the body of a case.
   void ActOnCaseStmtBody(Stmt *CaseStmt, Stmt *SubStmt);
 
   StmtResult ActOnDefaultStmt(SourceLocation DefaultLoc,
                               SourceLocation ColonLoc, Stmt *SubStmt,
                               Scope *CurScope);
   StmtResult ActOnLabelStmt(SourceLocation IdentLoc, LabelDecl *TheDecl,
                             SourceLocation ColonLoc, Stmt *SubStmt);
 
   StmtResult BuildAttributedStmt(SourceLocation AttrsLoc,
                                  ArrayRef<const Attr *> Attrs, Stmt *SubStmt);
   StmtResult ActOnAttributedStmt(const ParsedAttributes &AttrList,
                                  Stmt *SubStmt);
 
   /// Check whether the given statement can have musttail applied to it,
   /// issuing a diagnostic and returning false if not. In the success case,
   /// the statement is rewritten to remove implicit nodes from the return
   /// value.
   bool checkAndRewriteMustTailAttr(Stmt *St, const Attr &MTA);
 
   StmtResult ActOnIfStmt(SourceLocation IfLoc, IfStatementKind StatementKind,
                          SourceLocation LParenLoc, Stmt *InitStmt,
                          ConditionResult Cond, SourceLocation RParenLoc,
                          Stmt *ThenVal, SourceLocation ElseLoc, Stmt *ElseVal);
   StmtResult BuildIfStmt(SourceLocation IfLoc, IfStatementKind StatementKind,
                          SourceLocation LParenLoc, Stmt *InitStmt,
                          ConditionResult Cond, SourceLocation RParenLoc,
                          Stmt *ThenVal, SourceLocation ElseLoc, Stmt *ElseVal);
 
   ExprResult CheckSwitchCondition(SourceLocation SwitchLoc, Expr *Cond);
 
   StmtResult ActOnStartOfSwitchStmt(SourceLocation SwitchLoc,
                                     SourceLocation LParenLoc, Stmt *InitStmt,
                                     ConditionResult Cond,
                                     SourceLocation RParenLoc);
   StmtResult ActOnFinishSwitchStmt(SourceLocation SwitchLoc, Stmt *Switch,
                                    Stmt *Body);
 
   /// DiagnoseAssignmentEnum - Warn if assignment to enum is a constant
   /// integer not in the range of enum values.
   void DiagnoseAssignmentEnum(QualType DstType, QualType SrcType,
                               Expr *SrcExpr);
 
   StmtResult ActOnWhileStmt(SourceLocation WhileLoc, SourceLocation LParenLoc,
                             ConditionResult Cond, SourceLocation RParenLoc,
                             Stmt *Body);
   StmtResult ActOnDoStmt(SourceLocation DoLoc, Stmt *Body,
                          SourceLocation WhileLoc, SourceLocation CondLParen,
                          Expr *Cond, SourceLocation CondRParen);
 
   StmtResult ActOnForStmt(SourceLocation ForLoc, SourceLocation LParenLoc,
                           Stmt *First, ConditionResult Second,
                           FullExprArg Third, SourceLocation RParenLoc,
                           Stmt *Body);
 
   /// In an Objective C collection iteration statement:
   ///   for (x in y)
   /// x can be an arbitrary l-value expression.  Bind it up as a
   /// full-expression.
   StmtResult ActOnForEachLValueExpr(Expr *E);
 
   enum BuildForRangeKind {
     /// Initial building of a for-range statement.
     BFRK_Build,
     /// Instantiation or recovery rebuild of a for-range statement. Don't
     /// attempt any typo-correction.
     BFRK_Rebuild,
     /// Determining whether a for-range statement could be built. Avoid any
     /// unnecessary or irreversible actions.
     BFRK_Check
   };
 
   /// ActOnCXXForRangeStmt - Check and build a C++11 for-range statement.
   ///
   /// C++11 [stmt.ranged]:
   ///   A range-based for statement is equivalent to
   ///
   ///   {
   ///     auto && __range = range-init;
   ///     for ( auto __begin = begin-expr,
   ///           __end = end-expr;
   ///           __begin != __end;
   ///           ++__begin ) {
   ///       for-range-declaration = *__begin;
   ///       statement
   ///     }
   ///   }
   ///
   /// The body of the loop is not available yet, since it cannot be analysed
   /// until we have determined the type of the for-range-declaration.
   StmtResult ActOnCXXForRangeStmt(
       Scope *S, SourceLocation ForLoc, SourceLocation CoawaitLoc,
       Stmt *InitStmt, Stmt *LoopVar, SourceLocation ColonLoc, Expr *Collection,
       SourceLocation RParenLoc, BuildForRangeKind Kind,
       ArrayRef<MaterializeTemporaryExpr *> LifetimeExtendTemps = {});
 
   /// BuildCXXForRangeStmt - Build or instantiate a C++11 for-range statement.
   StmtResult BuildCXXForRangeStmt(
       SourceLocation ForLoc, SourceLocation CoawaitLoc, Stmt *InitStmt,
       SourceLocation ColonLoc, Stmt *RangeDecl, Stmt *Begin, Stmt *End,
       Expr *Cond, Expr *Inc, Stmt *LoopVarDecl, SourceLocation RParenLoc,
       BuildForRangeKind Kind,
       ArrayRef<MaterializeTemporaryExpr *> LifetimeExtendTemps = {});
 
   /// FinishCXXForRangeStmt - Attach the body to a C++0x for-range statement.
   /// This is a separate step from ActOnCXXForRangeStmt because analysis of the
   /// body cannot be performed until after the type of the range variable is
   /// determined.
   StmtResult FinishCXXForRangeStmt(Stmt *ForRange, Stmt *Body);
 
   StmtResult ActOnGotoStmt(SourceLocation GotoLoc, SourceLocation LabelLoc,
                            LabelDecl *TheDecl);
   StmtResult ActOnIndirectGotoStmt(SourceLocation GotoLoc,
                                    SourceLocation StarLoc, Expr *DestExp);
   StmtResult ActOnContinueStmt(SourceLocation ContinueLoc, Scope *CurScope);
   StmtResult ActOnBreakStmt(SourceLocation BreakLoc, Scope *CurScope);
 
   struct NamedReturnInfo {
     const VarDecl *Candidate;
 
     enum Status : uint8_t { None, MoveEligible, MoveEligibleAndCopyElidable };
     Status S;
 
     bool isMoveEligible() const { return S != None; };
     bool isCopyElidable() const { return S == MoveEligibleAndCopyElidable; }
   };
   enum class SimplerImplicitMoveMode { ForceOff, Normal, ForceOn };
 
   /// Determine whether the given expression might be move-eligible or
   /// copy-elidable in either a (co_)return statement or throw expression,
   /// without considering function return type, if applicable.
   ///
   /// \param E The expression being returned from the function or block,
   /// being thrown, or being co_returned from a coroutine. This expression
   /// might be modified by the implementation.
   ///
   /// \param Mode Overrides detection of current language mode
   /// and uses the rules for C++23.
   ///
   /// \returns An aggregate which contains the Candidate and isMoveEligible
   /// and isCopyElidable methods. If Candidate is non-null, it means
   /// isMoveEligible() would be true under the most permissive language
   /// standard.
   NamedReturnInfo getNamedReturnInfo(
       Expr *&E, SimplerImplicitMoveMode Mode = SimplerImplicitMoveMode::Normal);
 
   /// Determine whether the given NRVO candidate variable is move-eligible or
   /// copy-elidable, without considering function return type.
   ///
   /// \param VD The NRVO candidate variable.
   ///
   /// \returns An aggregate which contains the Candidate and isMoveEligible
   /// and isCopyElidable methods. If Candidate is non-null, it means
   /// isMoveEligible() would be true under the most permissive language
   /// standard.
   NamedReturnInfo getNamedReturnInfo(const VarDecl *VD);
 
   /// Updates given NamedReturnInfo's move-eligible and
   /// copy-elidable statuses, considering the function
   /// return type criteria as applicable to return statements.
   ///
   /// \param Info The NamedReturnInfo object to update.
   ///
   /// \param ReturnType This is the return type of the function.
   /// \returns The copy elision candidate, in case the initial return expression
   /// was copy elidable, or nullptr otherwise.
   const VarDecl *getCopyElisionCandidate(NamedReturnInfo &Info,
                                          QualType ReturnType);
 
   /// Perform the initialization of a potentially-movable value, which
   /// is the result of return value.
   ///
   /// This routine implements C++20 [class.copy.elision]p3, which attempts to
   /// treat returned lvalues as rvalues in certain cases (to prefer move
   /// construction), then falls back to treating them as lvalues if that failed.
   ExprResult
   PerformMoveOrCopyInitialization(const InitializedEntity &Entity,
                                   const NamedReturnInfo &NRInfo, Expr *Value,
                                   bool SupressSimplerImplicitMoves = false);
 
   TypeLoc getReturnTypeLoc(FunctionDecl *FD) const;
 
   /// Deduce the return type for a function from a returned expression, per
   /// C++1y [dcl.spec.auto]p6.
   bool DeduceFunctionTypeFromReturnExpr(FunctionDecl *FD,
                                         SourceLocation ReturnLoc, Expr *RetExpr,
                                         const AutoType *AT);
 
   StmtResult ActOnReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
                              Scope *CurScope);
   StmtResult BuildReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
                              bool AllowRecovery = false);
 
   /// ActOnCapScopeReturnStmt - Utility routine to type-check return statements
   /// for capturing scopes.
   StmtResult ActOnCapScopeReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
                                      NamedReturnInfo &NRInfo,
                                      bool SupressSimplerImplicitMoves);
 
   /// ActOnCXXCatchBlock - Takes an exception declaration and a handler block
   /// and creates a proper catch handler from them.
   StmtResult ActOnCXXCatchBlock(SourceLocation CatchLoc, Decl *ExDecl,
                                 Stmt *HandlerBlock);
 
   /// ActOnCXXTryBlock - Takes a try compound-statement and a number of
   /// handlers and creates a try statement from them.
   StmtResult ActOnCXXTryBlock(SourceLocation TryLoc, Stmt *TryBlock,
                               ArrayRef<Stmt *> Handlers);
 
   StmtResult ActOnSEHTryBlock(bool IsCXXTry, // try (true) or __try (false) ?
                               SourceLocation TryLoc, Stmt *TryBlock,
                               Stmt *Handler);
   StmtResult ActOnSEHExceptBlock(SourceLocation Loc, Expr *FilterExpr,
                                  Stmt *Block);
   void ActOnStartSEHFinallyBlock();
   void ActOnAbortSEHFinallyBlock();
   StmtResult ActOnFinishSEHFinallyBlock(SourceLocation Loc, Stmt *Block);
   StmtResult ActOnSEHLeaveStmt(SourceLocation Loc, Scope *CurScope);
 
   StmtResult BuildMSDependentExistsStmt(SourceLocation KeywordLoc,
                                         bool IsIfExists,
                                         NestedNameSpecifierLoc QualifierLoc,
                                         DeclarationNameInfo NameInfo,
                                         Stmt *Nested);
   StmtResult ActOnMSDependentExistsStmt(SourceLocation KeywordLoc,
                                         bool IsIfExists, CXXScopeSpec &SS,
                                         UnqualifiedId &Name, Stmt *Nested);
 
   void ActOnCapturedRegionStart(SourceLocation Loc, Scope *CurScope,
                                 CapturedRegionKind Kind, unsigned NumParams);
   typedef std::pair<StringRef, QualType> CapturedParamNameType;
   void ActOnCapturedRegionStart(SourceLocation Loc, Scope *CurScope,
                                 CapturedRegionKind Kind,
                                 ArrayRef<CapturedParamNameType> Params,
                                 unsigned OpenMPCaptureLevel = 0);
   StmtResult ActOnCapturedRegionEnd(Stmt *S);
   void ActOnCapturedRegionError();
   RecordDecl *CreateCapturedStmtRecordDecl(CapturedDecl *&CD,
                                            SourceLocation Loc,
                                            unsigned NumParams);
 
 private:
   /// Check whether the given statement can have musttail applied to it,
   /// issuing a diagnostic and returning false if not.
   bool checkMustTailAttr(const Stmt *St, const Attr &MTA);
 
   /// Check if the given expression contains 'break' or 'continue'
   /// statement that produces control flow different from GCC.
   void CheckBreakContinueBinding(Expr *E);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name `inline asm` Statement
   /// Implementations are in SemaStmtAsm.cpp
   ///@{
 
 public:
   StmtResult ActOnGCCAsmStmt(SourceLocation AsmLoc, bool IsSimple,
                              bool IsVolatile, unsigned NumOutputs,
                              unsigned NumInputs, IdentifierInfo **Names,
                              MultiExprArg Constraints, MultiExprArg Exprs,
                              Expr *AsmString, MultiExprArg Clobbers,
                              unsigned NumLabels, SourceLocation RParenLoc);
 
   void FillInlineAsmIdentifierInfo(Expr *Res,
                                    llvm::InlineAsmIdentifierInfo &Info);
   ExprResult LookupInlineAsmIdentifier(CXXScopeSpec &SS,
                                        SourceLocation TemplateKWLoc,
                                        UnqualifiedId &Id,
                                        bool IsUnevaluatedContext);
   bool LookupInlineAsmField(StringRef Base, StringRef Member, unsigned &Offset,
                             SourceLocation AsmLoc);
   ExprResult LookupInlineAsmVarDeclField(Expr *RefExpr, StringRef Member,
                                          SourceLocation AsmLoc);
   StmtResult ActOnMSAsmStmt(SourceLocation AsmLoc, SourceLocation LBraceLoc,
                             ArrayRef<Token> AsmToks, StringRef AsmString,
                             unsigned NumOutputs, unsigned NumInputs,
                             ArrayRef<StringRef> Constraints,
                             ArrayRef<StringRef> Clobbers,
                             ArrayRef<Expr *> Exprs, SourceLocation EndLoc);
   LabelDecl *GetOrCreateMSAsmLabel(StringRef ExternalLabelName,
                                    SourceLocation Location, bool AlwaysCreate);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Statement Attribute Handling
   /// Implementations are in SemaStmtAttr.cpp
   ///@{
 
 public:
   bool CheckNoInlineAttr(const Stmt *OrigSt, const Stmt *CurSt,
                          const AttributeCommonInfo &A);
   bool CheckAlwaysInlineAttr(const Stmt *OrigSt, const Stmt *CurSt,
                              const AttributeCommonInfo &A);
 
   CodeAlignAttr *BuildCodeAlignAttr(const AttributeCommonInfo &CI, Expr *E);
   bool CheckRebuiltStmtAttributes(ArrayRef<const Attr *> Attrs);
 
   /// Process the attributes before creating an attributed statement. Returns
   /// the semantic attributes that have been processed.
   void ProcessStmtAttributes(Stmt *Stmt, const ParsedAttributes &InAttrs,
                              SmallVectorImpl<const Attr *> &OutAttrs);
 
   ExprResult ActOnCXXAssumeAttr(Stmt *St, const ParsedAttr &A,
                                 SourceRange Range);
   ExprResult BuildCXXAssumeExpr(Expr *Assumption,
                                 const IdentifierInfo *AttrName,
                                 SourceRange Range);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Templates
   /// Implementations are in SemaTemplate.cpp
   ///@{
 
 public:
   // Saves the current floating-point pragma stack and clear it in this Sema.
   class FpPragmaStackSaveRAII {
   public:
     FpPragmaStackSaveRAII(Sema &S)
         : S(S), SavedStack(std::move(S.FpPragmaStack)) {
       S.FpPragmaStack.Stack.clear();
     }
     ~FpPragmaStackSaveRAII() { S.FpPragmaStack = std::move(SavedStack); }
 
   private:
     Sema &S;
     PragmaStack<FPOptionsOverride> SavedStack;
   };
 
   void resetFPOptions(FPOptions FPO) {
     CurFPFeatures = FPO;
     FpPragmaStack.CurrentValue = FPO.getChangesFrom(FPOptions(LangOpts));
   }
 
   ArrayRef<InventedTemplateParameterInfo> getInventedParameterInfos() const {
     return llvm::ArrayRef(InventedParameterInfos.begin() +
                               InventedParameterInfosStart,
                           InventedParameterInfos.end());
   }
 
   /// The number of SFINAE diagnostics that have been trapped.
   unsigned NumSFINAEErrors;
 
   ArrayRef<sema::FunctionScopeInfo *> getFunctionScopes() const {
     return llvm::ArrayRef(FunctionScopes.begin() + FunctionScopesStart,
                           FunctionScopes.end());
   }
 
   typedef llvm::MapVector<const FunctionDecl *,
                           std::unique_ptr<LateParsedTemplate>>
       LateParsedTemplateMapT;
   LateParsedTemplateMapT LateParsedTemplateMap;
 
   /// Determine the number of levels of enclosing template parameters. This is
   /// only usable while parsing. Note that this does not include dependent
   /// contexts in which no template parameters have yet been declared, such as
   /// in a terse function template or generic lambda before the first 'auto' is
   /// encountered.
   unsigned getTemplateDepth(Scope *S) const;
 
   void FilterAcceptableTemplateNames(LookupResult &R,
                                      bool AllowFunctionTemplates = true,
                                      bool AllowDependent = true);
   bool hasAnyAcceptableTemplateNames(LookupResult &R,
                                      bool AllowFunctionTemplates = true,
                                      bool AllowDependent = true,
                                      bool AllowNonTemplateFunctions = false);
   /// Try to interpret the lookup result D as a template-name.
   ///
   /// \param D A declaration found by name lookup.
   /// \param AllowFunctionTemplates Whether function templates should be
   ///        considered valid results.
   /// \param AllowDependent Whether unresolved using declarations (that might
   ///        name templates) should be considered valid results.
   static NamedDecl *getAsTemplateNameDecl(NamedDecl *D,
                                           bool AllowFunctionTemplates = true,
                                           bool AllowDependent = true);
 
   enum TemplateNameIsRequiredTag { TemplateNameIsRequired };
   /// Whether and why a template name is required in this lookup.
   class RequiredTemplateKind {
   public:
     /// Template name is required if TemplateKWLoc is valid.
     RequiredTemplateKind(SourceLocation TemplateKWLoc = SourceLocation())
         : TemplateKW(TemplateKWLoc) {}
     /// Template name is unconditionally required.
     RequiredTemplateKind(TemplateNameIsRequiredTag) {}
 
     SourceLocation getTemplateKeywordLoc() const {
       return TemplateKW.value_or(SourceLocation());
     }
     bool hasTemplateKeyword() const {
       return getTemplateKeywordLoc().isValid();
     }
     bool isRequired() const { return TemplateKW != SourceLocation(); }
     explicit operator bool() const { return isRequired(); }
 
   private:
     std::optional<SourceLocation> TemplateKW;
   };
 
   enum class AssumedTemplateKind {
     /// This is not assumed to be a template name.
     None,
     /// This is assumed to be a template name because lookup found nothing.
     FoundNothing,
     /// This is assumed to be a template name because lookup found one or more
     /// functions (but no function templates).
     FoundFunctions,
   };
 
   bool
   LookupTemplateName(LookupResult &R, Scope *S, CXXScopeSpec &SS,
                      QualType ObjectType, bool EnteringContext,
                      RequiredTemplateKind RequiredTemplate = SourceLocation(),
                      AssumedTemplateKind *ATK = nullptr,
                      bool AllowTypoCorrection = true);
 
   TemplateNameKind isTemplateName(Scope *S, CXXScopeSpec &SS,
                                   bool hasTemplateKeyword,
                                   const UnqualifiedId &Name,
                                   ParsedType ObjectType, bool EnteringContext,
                                   TemplateTy &Template,
                                   bool &MemberOfUnknownSpecialization,
                                   bool Disambiguation = false);
 
   /// Try to resolve an undeclared template name as a type template.
   ///
   /// Sets II to the identifier corresponding to the template name, and updates
   /// Name to a corresponding (typo-corrected) type template name and TNK to
   /// the corresponding kind, if possible.
   void ActOnUndeclaredTypeTemplateName(Scope *S, TemplateTy &Name,
                                        TemplateNameKind &TNK,
                                        SourceLocation NameLoc,
                                        IdentifierInfo *&II);
 
   bool resolveAssumedTemplateNameAsType(Scope *S, TemplateName &Name,
                                         SourceLocation NameLoc,
                                         bool Diagnose = true);
 
   /// Determine whether a particular identifier might be the name in a C++1z
   /// deduction-guide declaration.
   bool isDeductionGuideName(Scope *S, const IdentifierInfo &Name,
                             SourceLocation NameLoc, CXXScopeSpec &SS,
                             ParsedTemplateTy *Template = nullptr);
 
   bool DiagnoseUnknownTemplateName(const IdentifierInfo &II,
                                    SourceLocation IILoc, Scope *S,
                                    const CXXScopeSpec *SS,
                                    TemplateTy &SuggestedTemplate,
                                    TemplateNameKind &SuggestedKind);
 
   /// Determine whether we would be unable to instantiate this template (because
   /// it either has no definition, or is in the process of being instantiated).
   bool DiagnoseUninstantiableTemplate(SourceLocation PointOfInstantiation,
                                       NamedDecl *Instantiation,
                                       bool InstantiatedFromMember,
                                       const NamedDecl *Pattern,
                                       const NamedDecl *PatternDef,
                                       TemplateSpecializationKind TSK,
                                       bool Complain = true);
 
   /// DiagnoseTemplateParameterShadow - Produce a diagnostic complaining
   /// that the template parameter 'PrevDecl' is being shadowed by a new
   /// declaration at location Loc. Returns true to indicate that this is
   /// an error, and false otherwise.
   ///
   /// \param Loc The location of the declaration that shadows a template
   ///            parameter.
   ///
   /// \param PrevDecl The template parameter that the declaration shadows.
   ///
   /// \param SupportedForCompatibility Whether to issue the diagnostic as
   ///        a warning for compatibility with older versions of clang.
   ///        Ignored when MSVC compatibility is enabled.
   void DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl,
                                        bool SupportedForCompatibility = false);
 
   /// AdjustDeclIfTemplate - If the given decl happens to be a template, reset
   /// the parameter D to reference the templated declaration and return a
   /// pointer to the template declaration. Otherwise, do nothing to D and return
   /// null.
   TemplateDecl *AdjustDeclIfTemplate(Decl *&Decl);
 
   /// ActOnTypeParameter - Called when a C++ template type parameter
   /// (e.g., "typename T") has been parsed. Typename specifies whether
   /// the keyword "typename" was used to declare the type parameter
   /// (otherwise, "class" was used), and KeyLoc is the location of the
   /// "class" or "typename" keyword. ParamName is the name of the
   /// parameter (NULL indicates an unnamed template parameter) and
   /// ParamNameLoc is the location of the parameter name (if any).
   /// If the type parameter has a default argument, it will be added
   /// later via ActOnTypeParameterDefault.
   NamedDecl *ActOnTypeParameter(Scope *S, bool Typename,
                                 SourceLocation EllipsisLoc,
                                 SourceLocation KeyLoc,
                                 IdentifierInfo *ParamName,
                                 SourceLocation ParamNameLoc, unsigned Depth,
                                 unsigned Position, SourceLocation EqualLoc,
                                 ParsedType DefaultArg, bool HasTypeConstraint);
 
   bool CheckTypeConstraint(TemplateIdAnnotation *TypeConstraint);
 
   bool ActOnTypeConstraint(const CXXScopeSpec &SS,
                            TemplateIdAnnotation *TypeConstraint,
                            TemplateTypeParmDecl *ConstrainedParameter,
                            SourceLocation EllipsisLoc);
   bool BuildTypeConstraint(const CXXScopeSpec &SS,
                            TemplateIdAnnotation *TypeConstraint,
                            TemplateTypeParmDecl *ConstrainedParameter,
                            SourceLocation EllipsisLoc,
                            bool AllowUnexpandedPack);
 
   /// Attach a type-constraint to a template parameter.
   /// \returns true if an error occurred. This can happen if the
   /// immediately-declared constraint could not be formed (e.g. incorrect number
   /// of arguments for the named concept).
   bool AttachTypeConstraint(NestedNameSpecifierLoc NS,
                             DeclarationNameInfo NameInfo,
                             ConceptDecl *NamedConcept, NamedDecl *FoundDecl,
                             const TemplateArgumentListInfo *TemplateArgs,
                             TemplateTypeParmDecl *ConstrainedParameter,
                             QualType ConstrainedType,
                             SourceLocation EllipsisLoc);
 
   bool AttachTypeConstraint(AutoTypeLoc TL,
                             NonTypeTemplateParmDecl *NewConstrainedParm,
                             NonTypeTemplateParmDecl *OrigConstrainedParm,
                             SourceLocation EllipsisLoc);
 
   /// Require the given type to be a structural type, and diagnose if it is not.
   ///
   /// \return \c true if an error was produced.
   bool RequireStructuralType(QualType T, SourceLocation Loc);
 
   /// Check that the type of a non-type template parameter is
   /// well-formed.
   ///
   /// \returns the (possibly-promoted) parameter type if valid;
   /// otherwise, produces a diagnostic and returns a NULL type.
   QualType CheckNonTypeTemplateParameterType(TypeSourceInfo *&TSI,
                                              SourceLocation Loc);
   QualType CheckNonTypeTemplateParameterType(QualType T, SourceLocation Loc);
 
   NamedDecl *ActOnNonTypeTemplateParameter(Scope *S, Declarator &D,
                                            unsigned Depth, unsigned Position,
                                            SourceLocation EqualLoc,
                                            Expr *DefaultArg);
 
   /// ActOnTemplateTemplateParameter - Called when a C++ template template
   /// parameter (e.g. T in template <template \<typename> class T> class array)
   /// has been parsed. S is the current scope.
   NamedDecl *ActOnTemplateTemplateParameter(
       Scope *S, SourceLocation TmpLoc, TemplateParameterList *Params,
       bool Typename, SourceLocation EllipsisLoc, IdentifierInfo *ParamName,
       SourceLocation ParamNameLoc, unsigned Depth, unsigned Position,
       SourceLocation EqualLoc, ParsedTemplateArgument DefaultArg);
 
   /// ActOnTemplateParameterList - Builds a TemplateParameterList, optionally
   /// constrained by RequiresClause, that contains the template parameters in
   /// Params.
   TemplateParameterList *ActOnTemplateParameterList(
       unsigned Depth, SourceLocation ExportLoc, SourceLocation TemplateLoc,
       SourceLocation LAngleLoc, ArrayRef<NamedDecl *> Params,
       SourceLocation RAngleLoc, Expr *RequiresClause);
 
   /// The context in which we are checking a template parameter list.
   enum TemplateParamListContext {
     // For this context, Class, Variable, TypeAlias, and non-pack Template
     // Template Parameters are treated uniformly.
     TPC_Other,
 
     TPC_FunctionTemplate,
     TPC_ClassTemplateMember,
     TPC_FriendClassTemplate,
     TPC_FriendFunctionTemplate,
     TPC_FriendFunctionTemplateDefinition,
     TPC_TemplateTemplateParameterPack,
   };
 
   /// Checks the validity of a template parameter list, possibly
   /// considering the template parameter list from a previous
   /// declaration.
   ///
   /// If an "old" template parameter list is provided, it must be
   /// equivalent (per TemplateParameterListsAreEqual) to the "new"
   /// template parameter list.
   ///
   /// \param NewParams Template parameter list for a new template
   /// declaration. This template parameter list will be updated with any
   /// default arguments that are carried through from the previous
   /// template parameter list.
   ///
   /// \param OldParams If provided, template parameter list from a
   /// previous declaration of the same template. Default template
   /// arguments will be merged from the old template parameter list to
   /// the new template parameter list.
   ///
   /// \param TPC Describes the context in which we are checking the given
   /// template parameter list.
   ///
   /// \param SkipBody If we might have already made a prior merged definition
   /// of this template visible, the corresponding body-skipping information.
   /// Default argument redefinition is not an error when skipping such a body,
   /// because (under the ODR) we can assume the default arguments are the same
   /// as the prior merged definition.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CheckTemplateParameterList(TemplateParameterList *NewParams,
                                   TemplateParameterList *OldParams,
                                   TemplateParamListContext TPC,
                                   SkipBodyInfo *SkipBody = nullptr);
 
   /// Match the given template parameter lists to the given scope
   /// specifier, returning the template parameter list that applies to the
   /// name.
   ///
   /// \param DeclStartLoc the start of the declaration that has a scope
   /// specifier or a template parameter list.
   ///
   /// \param DeclLoc The location of the declaration itself.
   ///
   /// \param SS the scope specifier that will be matched to the given template
   /// parameter lists. This scope specifier precedes a qualified name that is
   /// being declared.
   ///
   /// \param TemplateId The template-id following the scope specifier, if there
   /// is one. Used to check for a missing 'template<>'.
   ///
   /// \param ParamLists the template parameter lists, from the outermost to the
   /// innermost template parameter lists.
   ///
   /// \param IsFriend Whether to apply the slightly different rules for
   /// matching template parameters to scope specifiers in friend
   /// declarations.
   ///
   /// \param IsMemberSpecialization will be set true if the scope specifier
   /// denotes a fully-specialized type, and therefore this is a declaration of
   /// a member specialization.
   ///
   /// \returns the template parameter list, if any, that corresponds to the
   /// name that is preceded by the scope specifier @p SS. This template
   /// parameter list may have template parameters (if we're declaring a
   /// template) or may have no template parameters (if we're declaring a
   /// template specialization), or may be NULL (if what we're declaring isn't
   /// itself a template).
   TemplateParameterList *MatchTemplateParametersToScopeSpecifier(
       SourceLocation DeclStartLoc, SourceLocation DeclLoc,
       const CXXScopeSpec &SS, TemplateIdAnnotation *TemplateId,
       ArrayRef<TemplateParameterList *> ParamLists, bool IsFriend,
       bool &IsMemberSpecialization, bool &Invalid,
       bool SuppressDiagnostic = false);
 
   /// Returns the template parameter list with all default template argument
   /// information.
   TemplateParameterList *GetTemplateParameterList(TemplateDecl *TD);
 
   DeclResult CheckClassTemplate(
       Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
       CXXScopeSpec &SS, IdentifierInfo *Name, SourceLocation NameLoc,
       const ParsedAttributesView &Attr, TemplateParameterList *TemplateParams,
       AccessSpecifier AS, SourceLocation ModulePrivateLoc,
       SourceLocation FriendLoc, unsigned NumOuterTemplateParamLists,
       TemplateParameterList **OuterTemplateParamLists,
       SkipBodyInfo *SkipBody = nullptr);
 
   /// Translates template arguments as provided by the parser
   /// into template arguments used by semantic analysis.
   void translateTemplateArguments(const ASTTemplateArgsPtr &In,
                                   TemplateArgumentListInfo &Out);
 
   /// Convert a parsed type into a parsed template argument. This is mostly
   /// trivial, except that we may have parsed a C++17 deduced class template
   /// specialization type, in which case we should form a template template
   /// argument instead of a type template argument.
   ParsedTemplateArgument ActOnTemplateTypeArgument(TypeResult ParsedType);
 
   void NoteAllFoundTemplates(TemplateName Name);
 
   QualType CheckTemplateIdType(TemplateName Template,
                                SourceLocation TemplateLoc,
                                TemplateArgumentListInfo &TemplateArgs);
 
   TypeResult
   ActOnTemplateIdType(Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                       TemplateTy Template, const IdentifierInfo *TemplateII,
                       SourceLocation TemplateIILoc, SourceLocation LAngleLoc,
                       ASTTemplateArgsPtr TemplateArgs, SourceLocation RAngleLoc,
                       bool IsCtorOrDtorName = false, bool IsClassName = false,
                       ImplicitTypenameContext AllowImplicitTypename =
                           ImplicitTypenameContext::No);
 
   /// Parsed an elaborated-type-specifier that refers to a template-id,
   /// such as \c class T::template apply<U>.
   TypeResult ActOnTagTemplateIdType(
       TagUseKind TUK, TypeSpecifierType TagSpec, SourceLocation TagLoc,
       CXXScopeSpec &SS, SourceLocation TemplateKWLoc, TemplateTy TemplateD,
       SourceLocation TemplateLoc, SourceLocation LAngleLoc,
       ASTTemplateArgsPtr TemplateArgsIn, SourceLocation RAngleLoc);
 
   DeclResult ActOnVarTemplateSpecialization(
       Scope *S, Declarator &D, TypeSourceInfo *DI, LookupResult &Previous,
       SourceLocation TemplateKWLoc, TemplateParameterList *TemplateParams,
       StorageClass SC, bool IsPartialSpecialization);
 
   /// Get the specialization of the given variable template corresponding to
   /// the specified argument list, or a null-but-valid result if the arguments
   /// are dependent.
   DeclResult CheckVarTemplateId(VarTemplateDecl *Template,
                                 SourceLocation TemplateLoc,
                                 SourceLocation TemplateNameLoc,
                                 const TemplateArgumentListInfo &TemplateArgs);
 
   /// Form a reference to the specialization of the given variable template
   /// corresponding to the specified argument list, or a null-but-valid result
   /// if the arguments are dependent.
   ExprResult CheckVarTemplateId(const CXXScopeSpec &SS,
                                 const DeclarationNameInfo &NameInfo,
                                 VarTemplateDecl *Template, NamedDecl *FoundD,
                                 SourceLocation TemplateLoc,
                                 const TemplateArgumentListInfo *TemplateArgs);
 
   ExprResult
   CheckConceptTemplateId(const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                          const DeclarationNameInfo &ConceptNameInfo,
                          NamedDecl *FoundDecl, ConceptDecl *NamedConcept,
                          const TemplateArgumentListInfo *TemplateArgs);
 
   void diagnoseMissingTemplateArguments(TemplateName Name, SourceLocation Loc);
   void diagnoseMissingTemplateArguments(const CXXScopeSpec &SS,
                                         bool TemplateKeyword, TemplateDecl *TD,
                                         SourceLocation Loc);
 
   ExprResult BuildTemplateIdExpr(const CXXScopeSpec &SS,
                                  SourceLocation TemplateKWLoc, LookupResult &R,
                                  bool RequiresADL,
                                  const TemplateArgumentListInfo *TemplateArgs);
 
   // We actually only call this from template instantiation.
   ExprResult
   BuildQualifiedTemplateIdExpr(CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                                const DeclarationNameInfo &NameInfo,
                                const TemplateArgumentListInfo *TemplateArgs,
                                bool IsAddressOfOperand);
 
   /// Form a template name from a name that is syntactically required to name a
   /// template, either due to use of the 'template' keyword or because a name in
   /// this syntactic context is assumed to name a template (C++
   /// [temp.names]p2-4).
   ///
   /// This action forms a template name given the name of the template and its
   /// optional scope specifier. This is used when the 'template' keyword is used
   /// or when the parsing context unambiguously treats a following '<' as
   /// introducing a template argument list. Note that this may produce a
   /// non-dependent template name if we can perform the lookup now and identify
   /// the named template.
   ///
   /// For example, given "x.MetaFun::template apply", the scope specifier
   /// \p SS will be "MetaFun::", \p TemplateKWLoc contains the location
   /// of the "template" keyword, and "apply" is the \p Name.
   TemplateNameKind ActOnTemplateName(Scope *S, CXXScopeSpec &SS,
                                      SourceLocation TemplateKWLoc,
                                      const UnqualifiedId &Name,
                                      ParsedType ObjectType,
                                      bool EnteringContext, TemplateTy &Template,
                                      bool AllowInjectedClassName = false);
 
   DeclResult ActOnClassTemplateSpecialization(
       Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,
       SourceLocation ModulePrivateLoc, CXXScopeSpec &SS,
       TemplateIdAnnotation &TemplateId, const ParsedAttributesView &Attr,
       MultiTemplateParamsArg TemplateParameterLists,
       SkipBodyInfo *SkipBody = nullptr);
 
   /// Check the non-type template arguments of a class template
   /// partial specialization according to C++ [temp.class.spec]p9.
   ///
   /// \param TemplateNameLoc the location of the template name.
   /// \param PrimaryTemplate the template parameters of the primary class
   ///        template.
   /// \param NumExplicit the number of explicitly-specified template arguments.
   /// \param TemplateArgs the template arguments of the class template
   ///        partial specialization.
   ///
   /// \returns \c true if there was an error, \c false otherwise.
   bool CheckTemplatePartialSpecializationArgs(SourceLocation Loc,
                                               TemplateDecl *PrimaryTemplate,
                                               unsigned NumExplicitArgs,
                                               ArrayRef<TemplateArgument> Args);
   void CheckTemplatePartialSpecialization(
       ClassTemplatePartialSpecializationDecl *Partial);
   void CheckTemplatePartialSpecialization(
       VarTemplatePartialSpecializationDecl *Partial);
 
   Decl *ActOnTemplateDeclarator(Scope *S,
                                 MultiTemplateParamsArg TemplateParameterLists,
                                 Declarator &D);
 
   /// Diagnose cases where we have an explicit template specialization
   /// before/after an explicit template instantiation, producing diagnostics
   /// for those cases where they are required and determining whether the
   /// new specialization/instantiation will have any effect.
   ///
   /// \param NewLoc the location of the new explicit specialization or
   /// instantiation.
   ///
   /// \param NewTSK the kind of the new explicit specialization or
   /// instantiation.
   ///
   /// \param PrevDecl the previous declaration of the entity.
   ///
   /// \param PrevTSK the kind of the old explicit specialization or
   /// instantiatin.
   ///
   /// \param PrevPointOfInstantiation if valid, indicates where the previous
   /// declaration was instantiated (either implicitly or explicitly).
   ///
   /// \param HasNoEffect will be set to true to indicate that the new
   /// specialization or instantiation has no effect and should be ignored.
   ///
   /// \returns true if there was an error that should prevent the introduction
   /// of the new declaration into the AST, false otherwise.
   bool CheckSpecializationInstantiationRedecl(
       SourceLocation NewLoc,
       TemplateSpecializationKind ActOnExplicitInstantiationNewTSK,
       NamedDecl *PrevDecl, TemplateSpecializationKind PrevTSK,
       SourceLocation PrevPtOfInstantiation, bool &SuppressNew);
 
   /// Perform semantic analysis for the given dependent function
   /// template specialization.
   ///
   /// The only possible way to get a dependent function template specialization
   /// is with a friend declaration, like so:
   ///
   /// \code
   ///   template \<class T> void foo(T);
   ///   template \<class T> class A {
   ///     friend void foo<>(T);
   ///   };
   /// \endcode
   ///
   /// There really isn't any useful analysis we can do here, so we
   /// just store the information.
   bool CheckDependentFunctionTemplateSpecialization(
       FunctionDecl *FD, const TemplateArgumentListInfo *ExplicitTemplateArgs,
       LookupResult &Previous);
 
   /// Perform semantic analysis for the given function template
   /// specialization.
   ///
   /// This routine performs all of the semantic analysis required for an
   /// explicit function template specialization. On successful completion,
   /// the function declaration \p FD will become a function template
   /// specialization.
   ///
   /// \param FD the function declaration, which will be updated to become a
   /// function template specialization.
   ///
   /// \param ExplicitTemplateArgs the explicitly-provided template arguments,
   /// if any. Note that this may be valid info even when 0 arguments are
   /// explicitly provided as in, e.g., \c void sort<>(char*, char*);
   /// as it anyway contains info on the angle brackets locations.
   ///
   /// \param Previous the set of declarations that may be specialized by
   /// this function specialization.
   ///
   /// \param QualifiedFriend whether this is a lookup for a qualified friend
   /// declaration with no explicit template argument list that might be
   /// befriending a function template specialization.
   bool CheckFunctionTemplateSpecialization(
       FunctionDecl *FD, TemplateArgumentListInfo *ExplicitTemplateArgs,
       LookupResult &Previous, bool QualifiedFriend = false);
 
   /// Perform semantic analysis for the given non-template member
   /// specialization.
   ///
   /// This routine performs all of the semantic analysis required for an
   /// explicit member function specialization. On successful completion,
   /// the function declaration \p FD will become a member function
   /// specialization.
   ///
   /// \param Member the member declaration, which will be updated to become a
   /// specialization.
   ///
   /// \param Previous the set of declarations, one of which may be specialized
   /// by this function specialization;  the set will be modified to contain the
   /// redeclared member.
   bool CheckMemberSpecialization(NamedDecl *Member, LookupResult &Previous);
   void CompleteMemberSpecialization(NamedDecl *Member, LookupResult &Previous);
 
   // Explicit instantiation of a class template specialization
   DeclResult ActOnExplicitInstantiation(
       Scope *S, SourceLocation ExternLoc, SourceLocation TemplateLoc,
       unsigned TagSpec, SourceLocation KWLoc, const CXXScopeSpec &SS,
       TemplateTy Template, SourceLocation TemplateNameLoc,
       SourceLocation LAngleLoc, ASTTemplateArgsPtr TemplateArgs,
       SourceLocation RAngleLoc, const ParsedAttributesView &Attr);
 
   // Explicit instantiation of a member class of a class template.
   DeclResult ActOnExplicitInstantiation(Scope *S, SourceLocation ExternLoc,
                                         SourceLocation TemplateLoc,
                                         unsigned TagSpec, SourceLocation KWLoc,
                                         CXXScopeSpec &SS, IdentifierInfo *Name,
                                         SourceLocation NameLoc,
                                         const ParsedAttributesView &Attr);
 
   DeclResult ActOnExplicitInstantiation(Scope *S, SourceLocation ExternLoc,
                                         SourceLocation TemplateLoc,
                                         Declarator &D);
 
   /// If the given template parameter has a default template
   /// argument, substitute into that default template argument and
   /// return the corresponding template argument.
   TemplateArgumentLoc SubstDefaultTemplateArgumentIfAvailable(
       TemplateDecl *Template, SourceLocation TemplateLoc,
       SourceLocation RAngleLoc, Decl *Param,
       ArrayRef<TemplateArgument> SugaredConverted,
       ArrayRef<TemplateArgument> CanonicalConverted, bool &HasDefaultArg);
 
   /// Returns the top most location responsible for the definition of \p N.
   /// If \p N is a a template specialization, this is the location
   /// of the top of the instantiation stack.
   /// Otherwise, the location of \p N is returned.
   SourceLocation getTopMostPointOfInstantiation(const NamedDecl *) const;
 
   /// Specifies the context in which a particular template
   /// argument is being checked.
   enum CheckTemplateArgumentKind {
     /// The template argument was specified in the code or was
     /// instantiated with some deduced template arguments.
     CTAK_Specified,
 
     /// The template argument was deduced via template argument
     /// deduction.
     CTAK_Deduced,
 
     /// The template argument was deduced from an array bound
     /// via template argument deduction.
     CTAK_DeducedFromArrayBound
   };
 
   struct CheckTemplateArgumentInfo {
     explicit CheckTemplateArgumentInfo(bool PartialOrdering = false,
                                        bool MatchingTTP = false)
         : PartialOrdering(PartialOrdering), MatchingTTP(MatchingTTP) {}
     CheckTemplateArgumentInfo(const CheckTemplateArgumentInfo &) = delete;
     CheckTemplateArgumentInfo &
     operator=(const CheckTemplateArgumentInfo &) = delete;
 
     /// The checked, converted argument will be added to the
     /// end of these vectors.
     SmallVector<TemplateArgument, 4> SugaredConverted, CanonicalConverted;
 
     /// The check is being performed in the context of partial ordering.
     bool PartialOrdering;
 
     /// If true, assume these template arguments are
     /// the injected template arguments for a template template parameter.
     /// This will relax the requirement that all its possible uses are valid:
     /// TTP checking is loose, and assumes that invalid uses will be diagnosed
     /// during instantiation.
     bool MatchingTTP;
 
     /// Is set to true when, in the context of TTP matching, a pack parameter
     /// matches non-pack arguments.
     bool MatchedPackOnParmToNonPackOnArg = false;
   };
 
   /// Check that the given template argument corresponds to the given
   /// template parameter.
   ///
   /// \param Param The template parameter against which the argument will be
   /// checked.
   ///
   /// \param Arg The template argument, which may be updated due to conversions.
   ///
   /// \param Template The template in which the template argument resides.
   ///
   /// \param TemplateLoc The location of the template name for the template
   /// whose argument list we're matching.
   ///
   /// \param RAngleLoc The location of the right angle bracket ('>') that closes
   /// the template argument list.
   ///
   /// \param ArgumentPackIndex The index into the argument pack where this
   /// argument will be placed. Only valid if the parameter is a parameter pack.
   ///
   /// \param CTAK Describes how we arrived at this particular template argument:
   /// explicitly written, deduced, etc.
   ///
   /// \returns true on error, false otherwise.
   bool CheckTemplateArgument(NamedDecl *Param, TemplateArgumentLoc &Arg,
                              NamedDecl *Template, SourceLocation TemplateLoc,
                              SourceLocation RAngleLoc,
                              unsigned ArgumentPackIndex,
                              CheckTemplateArgumentInfo &CTAI,
                              CheckTemplateArgumentKind CTAK);
 
   /// Check that the given template arguments can be provided to
   /// the given template, converting the arguments along the way.
   ///
   /// \param Template The template to which the template arguments are being
   /// provided.
   ///
   /// \param TemplateLoc The location of the template name in the source.
   ///
   /// \param TemplateArgs The list of template arguments. If the template is
   /// a template template parameter, this function may extend the set of
   /// template arguments to also include substituted, defaulted template
   /// arguments.
   ///
   /// \param PartialTemplateArgs True if the list of template arguments is
   /// intentionally partial, e.g., because we're checking just the initial
   /// set of template arguments.
   ///
   /// \param Converted Will receive the converted, canonicalized template
   /// arguments.
   ///
   /// \param UpdateArgsWithConversions If \c true, update \p TemplateArgs to
   /// contain the converted forms of the template arguments as written.
   /// Otherwise, \p TemplateArgs will not be modified.
   ///
   /// \param ConstraintsNotSatisfied If provided, and an error occurred, will
   /// receive true if the cause for the error is the associated constraints of
   /// the template not being satisfied by the template arguments.
   ///
   /// \param DefaultArgs any default arguments from template specialization
   /// deduction.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CheckTemplateArgumentList(TemplateDecl *Template,
                                  SourceLocation TemplateLoc,
                                  TemplateArgumentListInfo &TemplateArgs,
                                  const DefaultArguments &DefaultArgs,
                                  bool PartialTemplateArgs,
                                  CheckTemplateArgumentInfo &CTAI,
                                  bool UpdateArgsWithConversions = true,
                                  bool *ConstraintsNotSatisfied = nullptr);
 
   bool CheckTemplateTypeArgument(
       TemplateTypeParmDecl *Param, TemplateArgumentLoc &Arg,
       SmallVectorImpl<TemplateArgument> &SugaredConverted,
       SmallVectorImpl<TemplateArgument> &CanonicalConverted);
 
   /// Check a template argument against its corresponding
   /// template type parameter.
   ///
   /// This routine implements the semantics of C++ [temp.arg.type]. It
   /// returns true if an error occurred, and false otherwise.
   bool CheckTemplateArgument(TypeSourceInfo *Arg);
 
   /// Check a template argument against its corresponding
   /// non-type template parameter.
   ///
   /// This routine implements the semantics of C++ [temp.arg.nontype].
   /// If an error occurred, it returns ExprError(); otherwise, it
   /// returns the converted template argument. \p ParamType is the
   /// type of the non-type template parameter after it has been instantiated.
   ExprResult CheckTemplateArgument(NonTypeTemplateParmDecl *Param,
                                    QualType InstantiatedParamType, Expr *Arg,
                                    TemplateArgument &SugaredConverted,
                                    TemplateArgument &CanonicalConverted,
                                    bool MatchingTTP,
                                    CheckTemplateArgumentKind CTAK);
 
   /// Check a template argument against its corresponding
   /// template template parameter.
   ///
   /// This routine implements the semantics of C++ [temp.arg.template].
   /// It returns true if an error occurred, and false otherwise.
   bool CheckTemplateTemplateArgument(TemplateTemplateParmDecl *Param,
                                      TemplateParameterList *Params,
                                      TemplateArgumentLoc &Arg,
                                      bool PartialOrdering,
                                      bool *MatchedPackOnParmToNonPackOnArg);
 
   void NoteTemplateLocation(const NamedDecl &Decl,
                             std::optional<SourceRange> ParamRange = {});
   void NoteTemplateParameterLocation(const NamedDecl &Decl);
 
   /// Given a non-type template argument that refers to a
   /// declaration and the type of its corresponding non-type template
   /// parameter, produce an expression that properly refers to that
   /// declaration.
   /// FIXME: This is used in some contexts where the resulting expression
   /// doesn't need to live too long. It would be useful if this function
   /// could return a temporary expression.
   ExprResult BuildExpressionFromDeclTemplateArgument(
       const TemplateArgument &Arg, QualType ParamType, SourceLocation Loc,
       NamedDecl *TemplateParam = nullptr);
   ExprResult
   BuildExpressionFromNonTypeTemplateArgument(const TemplateArgument &Arg,
                                              SourceLocation Loc);
 
   /// Enumeration describing how template parameter lists are compared
   /// for equality.
   enum TemplateParameterListEqualKind {
     /// We are matching the template parameter lists of two templates
     /// that might be redeclarations.
     ///
     /// \code
     /// template<typename T> struct X;
     /// template<typename T> struct X;
     /// \endcode
     TPL_TemplateMatch,
 
     /// We are matching the template parameter lists of two template
     /// template parameters as part of matching the template parameter lists
     /// of two templates that might be redeclarations.
     ///
     /// \code
     /// template<template<int I> class TT> struct X;
     /// template<template<int Value> class Other> struct X;
     /// \endcode
     TPL_TemplateTemplateParmMatch,
 
     /// We are matching the template parameter lists of a template
     /// template argument against the template parameter lists of a template
     /// template parameter.
     ///
     /// \code
     /// template<template<int Value> class Metafun> struct X;
     /// template<int Value> struct integer_c;
     /// X<integer_c> xic;
     /// \endcode
     TPL_TemplateTemplateArgumentMatch,
 
     /// We are determining whether the template-parameters are equivalent
     /// according to C++ [temp.over.link]/6. This comparison does not consider
     /// constraints.
     ///
     /// \code
     /// template<C1 T> void f(T);
     /// template<C2 T> void f(T);
     /// \endcode
     TPL_TemplateParamsEquivalent,
   };
 
   // A struct to represent the 'new' declaration, which is either itself just
   // the named decl, or the important information we need about it in order to
   // do constraint comparisons.
   class TemplateCompareNewDeclInfo {
     const NamedDecl *ND = nullptr;
     const DeclContext *DC = nullptr;
     const DeclContext *LexicalDC = nullptr;
     SourceLocation Loc;
 
   public:
     TemplateCompareNewDeclInfo(const NamedDecl *ND) : ND(ND) {}
     TemplateCompareNewDeclInfo(const DeclContext *DeclCtx,
                                const DeclContext *LexicalDeclCtx,
                                SourceLocation Loc)
 
         : DC(DeclCtx), LexicalDC(LexicalDeclCtx), Loc(Loc) {
       assert(DC && LexicalDC &&
              "Constructor only for cases where we have the information to put "
              "in here");
     }
 
     // If this was constructed with no information, we cannot do substitution
     // for constraint comparison, so make sure we can check that.
     bool isInvalid() const { return !ND && !DC; }
 
     const NamedDecl *getDecl() const { return ND; }
 
     bool ContainsDecl(const NamedDecl *ND) const { return this->ND == ND; }
 
     const DeclContext *getLexicalDeclContext() const {
       return ND ? ND->getLexicalDeclContext() : LexicalDC;
     }
 
     const DeclContext *getDeclContext() const {
       return ND ? ND->getDeclContext() : DC;
     }
 
     SourceLocation getLocation() const { return ND ? ND->getLocation() : Loc; }
   };
 
   /// Determine whether the given template parameter lists are
   /// equivalent.
   ///
   /// \param New  The new template parameter list, typically written in the
   /// source code as part of a new template declaration.
   ///
   /// \param Old  The old template parameter list, typically found via
   /// name lookup of the template declared with this template parameter
   /// list.
   ///
   /// \param Complain  If true, this routine will produce a diagnostic if
   /// the template parameter lists are not equivalent.
   ///
   /// \param Kind describes how we are to match the template parameter lists.
   ///
   /// \param TemplateArgLoc If this source location is valid, then we
   /// are actually checking the template parameter list of a template
   /// argument (New) against the template parameter list of its
   /// corresponding template template parameter (Old). We produce
   /// slightly different diagnostics in this scenario.
   ///
   /// \returns True if the template parameter lists are equal, false
   /// otherwise.
   bool TemplateParameterListsAreEqual(
       const TemplateCompareNewDeclInfo &NewInstFrom, TemplateParameterList *New,
       const NamedDecl *OldInstFrom, TemplateParameterList *Old, bool Complain,
       TemplateParameterListEqualKind Kind,
       SourceLocation TemplateArgLoc = SourceLocation());
 
   bool TemplateParameterListsAreEqual(
       TemplateParameterList *New, TemplateParameterList *Old, bool Complain,
       TemplateParameterListEqualKind Kind,
       SourceLocation TemplateArgLoc = SourceLocation()) {
     return TemplateParameterListsAreEqual(nullptr, New, nullptr, Old, Complain,
                                           Kind, TemplateArgLoc);
   }
 
   /// Check whether a template can be declared within this scope.
   ///
   /// If the template declaration is valid in this scope, returns
   /// false. Otherwise, issues a diagnostic and returns true.
   bool CheckTemplateDeclScope(Scope *S, TemplateParameterList *TemplateParams);
 
   /// Called when the parser has parsed a C++ typename
   /// specifier, e.g., "typename T::type".
   ///
   /// \param S The scope in which this typename type occurs.
   /// \param TypenameLoc the location of the 'typename' keyword
   /// \param SS the nested-name-specifier following the typename (e.g., 'T::').
   /// \param II the identifier we're retrieving (e.g., 'type' in the example).
   /// \param IdLoc the location of the identifier.
   /// \param IsImplicitTypename context where T::type refers to a type.
   TypeResult ActOnTypenameType(
       Scope *S, SourceLocation TypenameLoc, const CXXScopeSpec &SS,
       const IdentifierInfo &II, SourceLocation IdLoc,
       ImplicitTypenameContext IsImplicitTypename = ImplicitTypenameContext::No);
 
   /// Called when the parser has parsed a C++ typename
   /// specifier that ends in a template-id, e.g.,
   /// "typename MetaFun::template apply<T1, T2>".
   ///
   /// \param S The scope in which this typename type occurs.
   /// \param TypenameLoc the location of the 'typename' keyword
   /// \param SS the nested-name-specifier following the typename (e.g., 'T::').
   /// \param TemplateLoc the location of the 'template' keyword, if any.
   /// \param TemplateName The template name.
   /// \param TemplateII The identifier used to name the template.
   /// \param TemplateIILoc The location of the template name.
   /// \param LAngleLoc The location of the opening angle bracket  ('<').
   /// \param TemplateArgs The template arguments.
   /// \param RAngleLoc The location of the closing angle bracket  ('>').
   TypeResult
   ActOnTypenameType(Scope *S, SourceLocation TypenameLoc,
                     const CXXScopeSpec &SS, SourceLocation TemplateLoc,
                     TemplateTy TemplateName, const IdentifierInfo *TemplateII,
                     SourceLocation TemplateIILoc, SourceLocation LAngleLoc,
                     ASTTemplateArgsPtr TemplateArgs, SourceLocation RAngleLoc);
 
   QualType CheckTypenameType(ElaboratedTypeKeyword Keyword,
                              SourceLocation KeywordLoc,
                              NestedNameSpecifierLoc QualifierLoc,
                              const IdentifierInfo &II, SourceLocation IILoc,
                              TypeSourceInfo **TSI, bool DeducedTSTContext);
 
   QualType CheckTypenameType(ElaboratedTypeKeyword Keyword,
                              SourceLocation KeywordLoc,
                              NestedNameSpecifierLoc QualifierLoc,
                              const IdentifierInfo &II, SourceLocation IILoc,
                              bool DeducedTSTContext = true);
 
   /// Rebuilds a type within the context of the current instantiation.
   ///
   /// The type \p T is part of the type of an out-of-line member definition of
   /// a class template (or class template partial specialization) that was
   /// parsed and constructed before we entered the scope of the class template
   /// (or partial specialization thereof). This routine will rebuild that type
   /// now that we have entered the declarator's scope, which may produce
   /// different canonical types, e.g.,
   ///
   /// \code
   /// template<typename T>
   /// struct X {
   ///   typedef T* pointer;
   ///   pointer data();
   /// };
   ///
   /// template<typename T>
   /// typename X<T>::pointer X<T>::data() { ... }
   /// \endcode
   ///
   /// Here, the type "typename X<T>::pointer" will be created as a
   /// DependentNameType, since we do not know that we can look into X<T> when we
   /// parsed the type. This function will rebuild the type, performing the
   /// lookup of "pointer" in X<T> and returning an ElaboratedType whose
   /// canonical type is the same as the canonical type of T*, allowing the
   /// return types of the out-of-line definition and the declaration to match.
   TypeSourceInfo *RebuildTypeInCurrentInstantiation(TypeSourceInfo *T,
                                                     SourceLocation Loc,
                                                     DeclarationName Name);
   bool RebuildNestedNameSpecifierInCurrentInstantiation(CXXScopeSpec &SS);
 
   ExprResult RebuildExprInCurrentInstantiation(Expr *E);
 
   /// Rebuild the template parameters now that we know we're in a current
   /// instantiation.
   bool
   RebuildTemplateParamsInCurrentInstantiation(TemplateParameterList *Params);
 
   /// Produces a formatted string that describes the binding of
   /// template parameters to template arguments.
   std::string
   getTemplateArgumentBindingsText(const TemplateParameterList *Params,
                                   const TemplateArgumentList &Args);
 
   std::string
   getTemplateArgumentBindingsText(const TemplateParameterList *Params,
                                   const TemplateArgument *Args,
                                   unsigned NumArgs);
 
   void diagnoseExprIntendedAsTemplateName(Scope *S, ExprResult TemplateName,
                                           SourceLocation Less,
                                           SourceLocation Greater);
 
   /// ActOnDependentIdExpression - Handle a dependent id-expression that
   /// was just parsed.  This is only possible with an explicit scope
   /// specifier naming a dependent type.
   ExprResult ActOnDependentIdExpression(
       const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
       const DeclarationNameInfo &NameInfo, bool isAddressOfOperand,
       const TemplateArgumentListInfo *TemplateArgs);
 
   ExprResult
   BuildDependentDeclRefExpr(const CXXScopeSpec &SS,
                             SourceLocation TemplateKWLoc,
                             const DeclarationNameInfo &NameInfo,
                             const TemplateArgumentListInfo *TemplateArgs);
 
   // Calculates whether the expression Constraint depends on an enclosing
   // template, for the purposes of [temp.friend] p9.
   // TemplateDepth is the 'depth' of the friend function, which is used to
   // compare whether a declaration reference is referring to a containing
   // template, or just the current friend function. A 'lower' TemplateDepth in
   // the AST refers to a 'containing' template. As the constraint is
   // uninstantiated, this is relative to the 'top' of the TU.
   bool
   ConstraintExpressionDependsOnEnclosingTemplate(const FunctionDecl *Friend,
                                                  unsigned TemplateDepth,
                                                  const Expr *Constraint);
 
   /// Find the failed Boolean condition within a given Boolean
   /// constant expression, and describe it with a string.
   std::pair<Expr *, std::string> findFailedBooleanCondition(Expr *Cond);
 
   void CheckDeductionGuideTemplate(FunctionTemplateDecl *TD);
 
   ConceptDecl *ActOnStartConceptDefinition(
       Scope *S, MultiTemplateParamsArg TemplateParameterLists,
       const IdentifierInfo *Name, SourceLocation NameLoc);
 
   ConceptDecl *ActOnFinishConceptDefinition(Scope *S, ConceptDecl *C,
                                             Expr *ConstraintExpr,
                                             const ParsedAttributesView &Attrs);
 
   void CheckConceptRedefinition(ConceptDecl *NewDecl, LookupResult &Previous,
                                 bool &AddToScope);
   bool CheckConceptUseInDefinition(ConceptDecl *Concept, SourceLocation Loc);
 
   TypeResult ActOnDependentTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                                const CXXScopeSpec &SS,
                                const IdentifierInfo *Name,
                                SourceLocation TagLoc, SourceLocation NameLoc);
 
   void MarkAsLateParsedTemplate(FunctionDecl *FD, Decl *FnD,
                                 CachedTokens &Toks);
   void UnmarkAsLateParsedTemplate(FunctionDecl *FD);
   bool IsInsideALocalClassWithinATemplateFunction();
 
   /// We've found a use of a templated declaration that would trigger an
   /// implicit instantiation. Check that any relevant explicit specializations
   /// and partial specializations are visible/reachable, and diagnose if not.
   void checkSpecializationVisibility(SourceLocation Loc, NamedDecl *Spec);
   void checkSpecializationReachability(SourceLocation Loc, NamedDecl *Spec);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Template Argument Deduction
   /// Implementations are in SemaTemplateDeduction.cpp
   ///@{
 
 public:
   /// When true, access checking violations are treated as SFINAE
   /// failures rather than hard errors.
   bool AccessCheckingSFINAE;
 
   /// RAII class used to determine whether SFINAE has
   /// trapped any errors that occur during template argument
   /// deduction.
   class SFINAETrap {
     Sema &SemaRef;
     unsigned PrevSFINAEErrors;
     bool PrevInNonInstantiationSFINAEContext;
     bool PrevAccessCheckingSFINAE;
     bool PrevLastDiagnosticIgnored;
 
   public:
     explicit SFINAETrap(Sema &SemaRef, bool AccessCheckingSFINAE = false)
         : SemaRef(SemaRef), PrevSFINAEErrors(SemaRef.NumSFINAEErrors),
           PrevInNonInstantiationSFINAEContext(
               SemaRef.InNonInstantiationSFINAEContext),
           PrevAccessCheckingSFINAE(SemaRef.AccessCheckingSFINAE),
           PrevLastDiagnosticIgnored(
               SemaRef.getDiagnostics().isLastDiagnosticIgnored()) {
       if (!SemaRef.isSFINAEContext())
         SemaRef.InNonInstantiationSFINAEContext = true;
       SemaRef.AccessCheckingSFINAE = AccessCheckingSFINAE;
     }
 
     ~SFINAETrap() {
       SemaRef.NumSFINAEErrors = PrevSFINAEErrors;
       SemaRef.InNonInstantiationSFINAEContext =
           PrevInNonInstantiationSFINAEContext;
       SemaRef.AccessCheckingSFINAE = PrevAccessCheckingSFINAE;
       SemaRef.getDiagnostics().setLastDiagnosticIgnored(
           PrevLastDiagnosticIgnored);
     }
 
     /// Determine whether any SFINAE errors have been trapped.
     bool hasErrorOccurred() const {
       return SemaRef.NumSFINAEErrors > PrevSFINAEErrors;
     }
   };
 
   /// RAII class used to indicate that we are performing provisional
   /// semantic analysis to determine the validity of a construct, so
   /// typo-correction and diagnostics in the immediate context (not within
   /// implicitly-instantiated templates) should be suppressed.
   class TentativeAnalysisScope {
     Sema &SemaRef;
     // FIXME: Using a SFINAETrap for this is a hack.
     SFINAETrap Trap;
     bool PrevDisableTypoCorrection;
 
   public:
     explicit TentativeAnalysisScope(Sema &SemaRef)
         : SemaRef(SemaRef), Trap(SemaRef, true),
           PrevDisableTypoCorrection(SemaRef.DisableTypoCorrection) {
       SemaRef.DisableTypoCorrection = true;
     }
     ~TentativeAnalysisScope() {
       SemaRef.DisableTypoCorrection = PrevDisableTypoCorrection;
     }
   };
 
   /// For each declaration that involved template argument deduction, the
   /// set of diagnostics that were suppressed during that template argument
   /// deduction.
   ///
   /// FIXME: Serialize this structure to the AST file.
   typedef llvm::DenseMap<Decl *, SmallVector<PartialDiagnosticAt, 1>>
       SuppressedDiagnosticsMap;
   SuppressedDiagnosticsMap SuppressedDiagnostics;
 
   /// Compare types for equality with respect to possibly compatible
   /// function types (noreturn adjustment, implicit calling conventions). If any
   /// of parameter and argument is not a function, just perform type comparison.
   ///
   /// \param P the template parameter type.
   ///
   /// \param A the argument type.
   bool isSameOrCompatibleFunctionType(QualType Param, QualType Arg);
 
   /// Allocate a TemplateArgumentLoc where all locations have
   /// been initialized to the given location.
   ///
   /// \param Arg The template argument we are producing template argument
   /// location information for.
   ///
   /// \param NTTPType For a declaration template argument, the type of
   /// the non-type template parameter that corresponds to this template
   /// argument. Can be null if no type sugar is available to add to the
   /// type from the template argument.
   ///
   /// \param Loc The source location to use for the resulting template
   /// argument.
   TemplateArgumentLoc
   getTrivialTemplateArgumentLoc(const TemplateArgument &Arg, QualType NTTPType,
                                 SourceLocation Loc,
                                 NamedDecl *TemplateParam = nullptr);
 
   /// Get a template argument mapping the given template parameter to itself,
   /// e.g. for X in \c template<int X>, this would return an expression template
   /// argument referencing X.
   TemplateArgumentLoc getIdentityTemplateArgumentLoc(NamedDecl *Param,
                                                      SourceLocation Location);
 
   /// Adjust the type \p ArgFunctionType to match the calling convention,
   /// noreturn, and optionally the exception specification of \p FunctionType.
   /// Deduction often wants to ignore these properties when matching function
   /// types.
   QualType adjustCCAndNoReturn(QualType ArgFunctionType, QualType FunctionType,
                                bool AdjustExceptionSpec = false);
 
   TemplateDeductionResult
   DeduceTemplateArguments(ClassTemplatePartialSpecializationDecl *Partial,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &Info);
 
   TemplateDeductionResult
   DeduceTemplateArguments(VarTemplatePartialSpecializationDecl *Partial,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &Info);
 
   /// Deduce the template arguments of the given template from \p FromType.
   /// Used to implement the IsDeducible constraint for alias CTAD per C++
   /// [over.match.class.deduct]p4.
   ///
   /// It only supports class or type alias templates.
   TemplateDeductionResult
   DeduceTemplateArgumentsFromType(TemplateDecl *TD, QualType FromType,
                                   sema::TemplateDeductionInfo &Info);
 
   TemplateDeductionResult DeduceTemplateArguments(
       TemplateParameterList *TemplateParams, ArrayRef<TemplateArgument> Ps,
       ArrayRef<TemplateArgument> As, sema::TemplateDeductionInfo &Info,
       SmallVectorImpl<DeducedTemplateArgument> &Deduced,
       bool NumberOfArgumentsMustMatch);
 
   /// Substitute the explicitly-provided template arguments into the
   /// given function template according to C++ [temp.arg.explicit].
   ///
   /// \param FunctionTemplate the function template into which the explicit
   /// template arguments will be substituted.
   ///
   /// \param ExplicitTemplateArgs the explicitly-specified template
   /// arguments.
   ///
   /// \param Deduced the deduced template arguments, which will be populated
   /// with the converted and checked explicit template arguments.
   ///
   /// \param ParamTypes will be populated with the instantiated function
   /// parameters.
   ///
   /// \param FunctionType if non-NULL, the result type of the function template
   /// will also be instantiated and the pointed-to value will be updated with
   /// the instantiated function type.
   ///
   /// \param Info if substitution fails for any reason, this object will be
   /// populated with more information about the failure.
   ///
   /// \returns TemplateDeductionResult::Success if substitution was successful,
   /// or some failure condition.
   TemplateDeductionResult SubstituteExplicitTemplateArguments(
       FunctionTemplateDecl *FunctionTemplate,
       TemplateArgumentListInfo &ExplicitTemplateArgs,
       SmallVectorImpl<DeducedTemplateArgument> &Deduced,
       SmallVectorImpl<QualType> &ParamTypes, QualType *FunctionType,
       sema::TemplateDeductionInfo &Info);
 
   /// brief A function argument from which we performed template argument
   // deduction for a call.
   struct OriginalCallArg {
     OriginalCallArg(QualType OriginalParamType, bool DecomposedParam,
                     unsigned ArgIdx, QualType OriginalArgType)
         : OriginalParamType(OriginalParamType),
           DecomposedParam(DecomposedParam), ArgIdx(ArgIdx),
           OriginalArgType(OriginalArgType) {}
 
     QualType OriginalParamType;
     bool DecomposedParam;
     unsigned ArgIdx;
     QualType OriginalArgType;
   };
 
   /// Finish template argument deduction for a function template,
   /// checking the deduced template arguments for completeness and forming
   /// the function template specialization.
   ///
   /// \param OriginalCallArgs If non-NULL, the original call arguments against
   /// which the deduced argument types should be compared.
   TemplateDeductionResult FinishTemplateArgumentDeduction(
       FunctionTemplateDecl *FunctionTemplate,
       SmallVectorImpl<DeducedTemplateArgument> &Deduced,
       unsigned NumExplicitlySpecified, FunctionDecl *&Specialization,
       sema::TemplateDeductionInfo &Info,
       SmallVectorImpl<OriginalCallArg> const *OriginalCallArgs,
       bool PartialOverloading, bool PartialOrdering,
       llvm::function_ref<bool()> CheckNonDependent = [] { return false; });
 
   /// Perform template argument deduction from a function call
   /// (C++ [temp.deduct.call]).
   ///
   /// \param FunctionTemplate the function template for which we are performing
   /// template argument deduction.
   ///
   /// \param ExplicitTemplateArgs the explicit template arguments provided
   /// for this call.
   ///
   /// \param Args the function call arguments
   ///
   /// \param Specialization if template argument deduction was successful,
   /// this will be set to the function template specialization produced by
   /// template argument deduction.
   ///
   /// \param Info the argument will be updated to provide additional information
   /// about template argument deduction.
   ///
   /// \param CheckNonDependent A callback to invoke to check conversions for
   /// non-dependent parameters, between deduction and substitution, per DR1391.
   /// If this returns true, substitution will be skipped and we return
   /// TemplateDeductionResult::NonDependentConversionFailure. The callback is
   /// passed the parameter types (after substituting explicit template
   /// arguments).
   ///
   /// \returns the result of template argument deduction.
   TemplateDeductionResult DeduceTemplateArguments(
       FunctionTemplateDecl *FunctionTemplate,
       TemplateArgumentListInfo *ExplicitTemplateArgs, ArrayRef<Expr *> Args,
       FunctionDecl *&Specialization, sema::TemplateDeductionInfo &Info,
       bool PartialOverloading, bool AggregateDeductionCandidate,
       bool PartialOrdering, QualType ObjectType,
       Expr::Classification ObjectClassification,
       llvm::function_ref<bool(ArrayRef<QualType>)> CheckNonDependent);
 
   /// Deduce template arguments when taking the address of a function
   /// template (C++ [temp.deduct.funcaddr]) or matching a specialization to
   /// a template.
   ///
   /// \param FunctionTemplate the function template for which we are performing
   /// template argument deduction.
   ///
   /// \param ExplicitTemplateArgs the explicitly-specified template
   /// arguments.
   ///
   /// \param ArgFunctionType the function type that will be used as the
   /// "argument" type (A) when performing template argument deduction from the
   /// function template's function type. This type may be NULL, if there is no
   /// argument type to compare against, in C++0x [temp.arg.explicit]p3.
   ///
   /// \param Specialization if template argument deduction was successful,
   /// this will be set to the function template specialization produced by
   /// template argument deduction.
   ///
   /// \param Info the argument will be updated to provide additional information
   /// about template argument deduction.
   ///
   /// \param IsAddressOfFunction If \c true, we are deducing as part of taking
   /// the address of a function template per [temp.deduct.funcaddr] and
   /// [over.over]. If \c false, we are looking up a function template
   /// specialization based on its signature, per [temp.deduct.decl].
   ///
   /// \returns the result of template argument deduction.
   TemplateDeductionResult DeduceTemplateArguments(
       FunctionTemplateDecl *FunctionTemplate,
       TemplateArgumentListInfo *ExplicitTemplateArgs, QualType ArgFunctionType,
       FunctionDecl *&Specialization, sema::TemplateDeductionInfo &Info,
       bool IsAddressOfFunction = false);
 
   /// Deduce template arguments for a templated conversion
   /// function (C++ [temp.deduct.conv]) and, if successful, produce a
   /// conversion function template specialization.
   TemplateDeductionResult DeduceTemplateArguments(
       FunctionTemplateDecl *FunctionTemplate, QualType ObjectType,
       Expr::Classification ObjectClassification, QualType ToType,
       CXXConversionDecl *&Specialization, sema::TemplateDeductionInfo &Info);
 
   /// Deduce template arguments for a function template when there is
   /// nothing to deduce against (C++0x [temp.arg.explicit]p3).
   ///
   /// \param FunctionTemplate the function template for which we are performing
   /// template argument deduction.
   ///
   /// \param ExplicitTemplateArgs the explicitly-specified template
   /// arguments.
   ///
   /// \param Specialization if template argument deduction was successful,
   /// this will be set to the function template specialization produced by
   /// template argument deduction.
   ///
   /// \param Info the argument will be updated to provide additional information
   /// about template argument deduction.
   ///
   /// \param IsAddressOfFunction If \c true, we are deducing as part of taking
   /// the address of a function template in a context where we do not have a
   /// target type, per [over.over]. If \c false, we are looking up a function
   /// template specialization based on its signature, which only happens when
   /// deducing a function parameter type from an argument that is a template-id
   /// naming a function template specialization.
   ///
   /// \returns the result of template argument deduction.
   TemplateDeductionResult
   DeduceTemplateArguments(FunctionTemplateDecl *FunctionTemplate,
                           TemplateArgumentListInfo *ExplicitTemplateArgs,
                           FunctionDecl *&Specialization,
                           sema::TemplateDeductionInfo &Info,
                           bool IsAddressOfFunction = false);
 
   /// Substitute Replacement for \p auto in \p TypeWithAuto
   QualType SubstAutoType(QualType TypeWithAuto, QualType Replacement);
   /// Substitute Replacement for auto in TypeWithAuto
   TypeSourceInfo *SubstAutoTypeSourceInfo(TypeSourceInfo *TypeWithAuto,
                                           QualType Replacement);
 
   // Substitute auto in TypeWithAuto for a Dependent auto type
   QualType SubstAutoTypeDependent(QualType TypeWithAuto);
 
   // Substitute auto in TypeWithAuto for a Dependent auto type
   TypeSourceInfo *
   SubstAutoTypeSourceInfoDependent(TypeSourceInfo *TypeWithAuto);
 
   /// Completely replace the \c auto in \p TypeWithAuto by
   /// \p Replacement. This does not retain any \c auto type sugar.
   QualType ReplaceAutoType(QualType TypeWithAuto, QualType Replacement);
   TypeSourceInfo *ReplaceAutoTypeSourceInfo(TypeSourceInfo *TypeWithAuto,
                                             QualType Replacement);
 
   /// Deduce the type for an auto type-specifier (C++11 [dcl.spec.auto]p6)
   ///
   /// Note that this is done even if the initializer is dependent. (This is
   /// necessary to support partial ordering of templates using 'auto'.)
   /// A dependent type will be produced when deducing from a dependent type.
   ///
   /// \param Type the type pattern using the auto type-specifier.
   /// \param Init the initializer for the variable whose type is to be deduced.
   /// \param Result if type deduction was successful, this will be set to the
   ///        deduced type.
   /// \param Info the argument will be updated to provide additional information
   ///        about template argument deduction.
   /// \param DependentDeduction Set if we should permit deduction in
   ///        dependent cases. This is necessary for template partial ordering
   ///        with 'auto' template parameters. The template parameter depth to be
   ///        used should be specified in the 'Info' parameter.
   /// \param IgnoreConstraints Set if we should not fail if the deduced type
   ///                          does not satisfy the type-constraint in the auto
   ///                          type.
   TemplateDeductionResult
   DeduceAutoType(TypeLoc AutoTypeLoc, Expr *Initializer, QualType &Result,
                  sema::TemplateDeductionInfo &Info,
                  bool DependentDeduction = false,
                  bool IgnoreConstraints = false,
                  TemplateSpecCandidateSet *FailedTSC = nullptr);
   void DiagnoseAutoDeductionFailure(const VarDecl *VDecl, const Expr *Init);
   bool DeduceReturnType(FunctionDecl *FD, SourceLocation Loc,
                         bool Diagnose = true);
 
   bool CheckIfFunctionSpecializationIsImmediate(FunctionDecl *FD,
                                                 SourceLocation Loc);
 
   /// Returns the more specialized class template partial specialization
   /// according to the rules of partial ordering of class template partial
   /// specializations (C++ [temp.class.order]).
   ///
   /// \param PS1 the first class template partial specialization
   ///
   /// \param PS2 the second class template partial specialization
   ///
   /// \returns the more specialized class template partial specialization. If
   /// neither partial specialization is more specialized, returns NULL.
   ClassTemplatePartialSpecializationDecl *
   getMoreSpecializedPartialSpecialization(
       ClassTemplatePartialSpecializationDecl *PS1,
       ClassTemplatePartialSpecializationDecl *PS2, SourceLocation Loc);
 
   bool isMoreSpecializedThanPrimary(ClassTemplatePartialSpecializationDecl *T,
                                     sema::TemplateDeductionInfo &Info);
 
   VarTemplatePartialSpecializationDecl *getMoreSpecializedPartialSpecialization(
       VarTemplatePartialSpecializationDecl *PS1,
       VarTemplatePartialSpecializationDecl *PS2, SourceLocation Loc);
 
   bool isMoreSpecializedThanPrimary(VarTemplatePartialSpecializationDecl *T,
                                     sema::TemplateDeductionInfo &Info);
 
   bool isTemplateTemplateParameterAtLeastAsSpecializedAs(
       TemplateParameterList *PParam, TemplateDecl *PArg, TemplateDecl *AArg,
       const DefaultArguments &DefaultArgs, SourceLocation ArgLoc,
       bool PartialOrdering, bool *MatchedPackOnParmToNonPackOnArg);
 
   /// Mark which template parameters are used in a given expression.
   ///
   /// \param E the expression from which template parameters will be deduced.
   ///
   /// \param Used a bit vector whose elements will be set to \c true
   /// to indicate when the corresponding template parameter will be
   /// deduced.
   void MarkUsedTemplateParameters(const Expr *E, bool OnlyDeduced,
                                   unsigned Depth, llvm::SmallBitVector &Used);
 
   /// Mark which template parameters can be deduced from a given
   /// template argument list.
   ///
   /// \param TemplateArgs the template argument list from which template
   /// parameters will be deduced.
   ///
   /// \param Used a bit vector whose elements will be set to \c true
   /// to indicate when the corresponding template parameter will be
   /// deduced.
   void MarkUsedTemplateParameters(const TemplateArgumentList &TemplateArgs,
                                   bool OnlyDeduced, unsigned Depth,
                                   llvm::SmallBitVector &Used);
   void
   MarkDeducedTemplateParameters(const FunctionTemplateDecl *FunctionTemplate,
                                 llvm::SmallBitVector &Deduced) {
     return MarkDeducedTemplateParameters(Context, FunctionTemplate, Deduced);
   }
 
   /// Marks all of the template parameters that will be deduced by a
   /// call to the given function template.
   static void
   MarkDeducedTemplateParameters(ASTContext &Ctx,
                                 const FunctionTemplateDecl *FunctionTemplate,
                                 llvm::SmallBitVector &Deduced);
 
   /// Returns the more specialized function template according
   /// to the rules of function template partial ordering (C++
   /// [temp.func.order]).
   ///
   /// \param FT1 the first function template
   ///
   /// \param FT2 the second function template
   ///
   /// \param TPOC the context in which we are performing partial ordering of
   /// function templates.
   ///
   /// \param NumCallArguments1 The number of arguments in the call to FT1, used
   /// only when \c TPOC is \c TPOC_Call. Does not include the object argument
   /// when calling a member function.
   ///
   /// \param RawObj1Ty The type of the object parameter of FT1 if a member
   /// function only used if \c TPOC is \c TPOC_Call and FT1 is a Function
   /// template from a member function
   ///
   /// \param RawObj2Ty The type of the object parameter of FT2 if a member
   /// function only used if \c TPOC is \c TPOC_Call and FT2 is a Function
   /// template from a member function
   ///
   /// \param Reversed If \c true, exactly one of FT1 and FT2 is an overload
   /// candidate with a reversed parameter order. In this case, the corresponding
   /// P/A pairs between FT1 and FT2 are reversed.
   ///
   /// \returns the more specialized function template. If neither
   /// template is more specialized, returns NULL.
   FunctionTemplateDecl *getMoreSpecializedTemplate(
       FunctionTemplateDecl *FT1, FunctionTemplateDecl *FT2, SourceLocation Loc,
       TemplatePartialOrderingContext TPOC, unsigned NumCallArguments1,
       QualType RawObj1Ty = {}, QualType RawObj2Ty = {}, bool Reversed = false);
 
   /// Retrieve the most specialized of the given function template
   /// specializations.
   ///
   /// \param SpecBegin the start iterator of the function template
   /// specializations that we will be comparing.
   ///
   /// \param SpecEnd the end iterator of the function template
   /// specializations, paired with \p SpecBegin.
   ///
   /// \param Loc the location where the ambiguity or no-specializations
   /// diagnostic should occur.
   ///
   /// \param NoneDiag partial diagnostic used to diagnose cases where there are
   /// no matching candidates.
   ///
   /// \param AmbigDiag partial diagnostic used to diagnose an ambiguity, if one
   /// occurs.
   ///
   /// \param CandidateDiag partial diagnostic used for each function template
   /// specialization that is a candidate in the ambiguous ordering. One
   /// parameter in this diagnostic should be unbound, which will correspond to
   /// the string describing the template arguments for the function template
   /// specialization.
   ///
   /// \returns the most specialized function template specialization, if
   /// found. Otherwise, returns SpecEnd.
   UnresolvedSetIterator
   getMostSpecialized(UnresolvedSetIterator SBegin, UnresolvedSetIterator SEnd,
                      TemplateSpecCandidateSet &FailedCandidates,
                      SourceLocation Loc, const PartialDiagnostic &NoneDiag,
                      const PartialDiagnostic &AmbigDiag,
                      const PartialDiagnostic &CandidateDiag,
                      bool Complain = true, QualType TargetType = QualType());
 
   /// Returns the more constrained function according to the rules of
   /// partial ordering by constraints (C++ [temp.constr.order]).
   ///
   /// \param FD1 the first function
   ///
   /// \param FD2 the second function
   ///
   /// \returns the more constrained function. If neither function is
   /// more constrained, returns NULL.
   FunctionDecl *getMoreConstrainedFunction(FunctionDecl *FD1,
                                            FunctionDecl *FD2);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Template Deduction Guide
   /// Implementations are in SemaTemplateDeductionGuide.cpp
   ///@{
 
   /// Declare implicit deduction guides for a class template if we've
   /// not already done so.
   void DeclareImplicitDeductionGuides(TemplateDecl *Template,
                                       SourceLocation Loc);
 
   FunctionTemplateDecl *DeclareAggregateDeductionGuideFromInitList(
       TemplateDecl *Template, MutableArrayRef<QualType> ParamTypes,
       SourceLocation Loc);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Template Instantiation
   /// Implementations are in SemaTemplateInstantiate.cpp
   ///@{
 
 public:
   /// A helper class for building up ExtParameterInfos.
   class ExtParameterInfoBuilder {
     SmallVector<FunctionProtoType::ExtParameterInfo, 16> Infos;
     bool HasInteresting = false;
 
   public:
     /// Set the ExtParameterInfo for the parameter at the given index,
     ///
     void set(unsigned index, FunctionProtoType::ExtParameterInfo info) {
       assert(Infos.size() <= index);
       Infos.resize(index);
       Infos.push_back(info);
 
       if (!HasInteresting)
         HasInteresting = (info != FunctionProtoType::ExtParameterInfo());
     }
 
     /// Return a pointer (suitable for setting in an ExtProtoInfo) to the
     /// ExtParameterInfo array we've built up.
     const FunctionProtoType::ExtParameterInfo *
     getPointerOrNull(unsigned numParams) {
       if (!HasInteresting)
         return nullptr;
       Infos.resize(numParams);
       return Infos.data();
     }
   };
 
   /// The current instantiation scope used to store local
   /// variables.
   LocalInstantiationScope *CurrentInstantiationScope;
 
   typedef llvm::DenseMap<ParmVarDecl *, llvm::TinyPtrVector<ParmVarDecl *>>
       UnparsedDefaultArgInstantiationsMap;
 
   /// A mapping from parameters with unparsed default arguments to the
   /// set of instantiations of each parameter.
   ///
   /// This mapping is a temporary data structure used when parsing
   /// nested class templates or nested classes of class templates,
   /// where we might end up instantiating an inner class before the
   /// default arguments of its methods have been parsed.
   UnparsedDefaultArgInstantiationsMap UnparsedDefaultArgInstantiations;
 
   /// A context in which code is being synthesized (where a source location
   /// alone is not sufficient to identify the context). This covers template
   /// instantiation and various forms of implicitly-generated functions.
   struct CodeSynthesisContext {
     /// The kind of template instantiation we are performing
     enum SynthesisKind {
       /// We are instantiating a template declaration. The entity is
       /// the declaration we're instantiating (e.g., a CXXRecordDecl).
       TemplateInstantiation,
 
       /// We are instantiating a default argument for a template
       /// parameter. The Entity is the template parameter whose argument is
       /// being instantiated, the Template is the template, and the
       /// TemplateArgs/NumTemplateArguments provide the template arguments as
       /// specified.
       DefaultTemplateArgumentInstantiation,
 
       /// We are instantiating a default argument for a function.
       /// The Entity is the ParmVarDecl, and TemplateArgs/NumTemplateArgs
       /// provides the template arguments as specified.
       DefaultFunctionArgumentInstantiation,
 
       /// We are substituting explicit template arguments provided for
       /// a function template. The entity is a FunctionTemplateDecl.
       ExplicitTemplateArgumentSubstitution,
 
       /// We are substituting template argument determined as part of
       /// template argument deduction for either a class template
       /// partial specialization or a function template. The
       /// Entity is either a {Class|Var}TemplatePartialSpecializationDecl or
       /// a TemplateDecl.
       DeducedTemplateArgumentSubstitution,
 
       /// We are substituting into a lambda expression.
       LambdaExpressionSubstitution,
 
       /// We are substituting prior template arguments into a new
       /// template parameter. The template parameter itself is either a
       /// NonTypeTemplateParmDecl or a TemplateTemplateParmDecl.
       PriorTemplateArgumentSubstitution,
 
       /// We are checking the validity of a default template argument that
       /// has been used when naming a template-id.
       DefaultTemplateArgumentChecking,
 
       /// We are computing the exception specification for a defaulted special
       /// member function.
       ExceptionSpecEvaluation,
 
       /// We are instantiating the exception specification for a function
       /// template which was deferred until it was needed.
       ExceptionSpecInstantiation,
 
       /// We are instantiating a requirement of a requires expression.
       RequirementInstantiation,
 
       /// We are checking the satisfaction of a nested requirement of a requires
       /// expression.
       NestedRequirementConstraintsCheck,
 
       /// We are declaring an implicit special member function.
       DeclaringSpecialMember,
 
       /// We are declaring an implicit 'operator==' for a defaulted
       /// 'operator<=>'.
       DeclaringImplicitEqualityComparison,
 
       /// We are defining a synthesized function (such as a defaulted special
       /// member).
       DefiningSynthesizedFunction,
 
       // We are checking the constraints associated with a constrained entity or
       // the constraint expression of a concept. This includes the checks that
       // atomic constraints have the type 'bool' and that they can be constant
       // evaluated.
       ConstraintsCheck,
 
       // We are substituting template arguments into a constraint expression.
       ConstraintSubstitution,
 
       // We are normalizing a constraint expression.
       ConstraintNormalization,
 
       // Instantiating a Requires Expression parameter clause.
       RequirementParameterInstantiation,
 
       // We are substituting into the parameter mapping of an atomic constraint
       // during normalization.
       ParameterMappingSubstitution,
 
       /// We are rewriting a comparison operator in terms of an operator<=>.
       RewritingOperatorAsSpaceship,
 
       /// We are initializing a structured binding.
       InitializingStructuredBinding,
 
       /// We are marking a class as __dllexport.
       MarkingClassDllexported,
 
       /// We are building an implied call from __builtin_dump_struct. The
       /// arguments are in CallArgs.
       BuildingBuiltinDumpStructCall,
 
       /// Added for Template instantiation observation.
       /// Memoization means we are _not_ instantiating a template because
       /// it is already instantiated (but we entered a context where we
       /// would have had to if it was not already instantiated).
       Memoization,
 
       /// We are building deduction guides for a class.
       BuildingDeductionGuides,
 
       /// We are instantiating a type alias template declaration.
       TypeAliasTemplateInstantiation,
 
       /// We are performing partial ordering for template template parameters.
       PartialOrderingTTP,
     } Kind;
 
     /// Was the enclosing context a non-instantiation SFINAE context?
     bool SavedInNonInstantiationSFINAEContext;
 
     /// The point of instantiation or synthesis within the source code.
     SourceLocation PointOfInstantiation;
 
     /// The entity that is being synthesized.
     Decl *Entity;
 
     /// The template (or partial specialization) in which we are
     /// performing the instantiation, for substitutions of prior template
     /// arguments.
     NamedDecl *Template;
 
     union {
       /// The list of template arguments we are substituting, if they
       /// are not part of the entity.
       const TemplateArgument *TemplateArgs;
 
       /// The list of argument expressions in a synthesized call.
       const Expr *const *CallArgs;
     };
 
     // FIXME: Wrap this union around more members, or perhaps store the
     // kind-specific members in the RAII object owning the context.
     union {
       /// The number of template arguments in TemplateArgs.
       unsigned NumTemplateArgs;
 
       /// The number of expressions in CallArgs.
       unsigned NumCallArgs;
 
       /// The special member being declared or defined.
       CXXSpecialMemberKind SpecialMember;
     };
 
     ArrayRef<TemplateArgument> template_arguments() const {
       assert(Kind != DeclaringSpecialMember);
       return {TemplateArgs, NumTemplateArgs};
     }
 
     /// The template deduction info object associated with the
     /// substitution or checking of explicit or deduced template arguments.
     sema::TemplateDeductionInfo *DeductionInfo;
 
     /// The source range that covers the construct that cause
     /// the instantiation, e.g., the template-id that causes a class
     /// template instantiation.
     SourceRange InstantiationRange;
 
     CodeSynthesisContext()
         : Kind(TemplateInstantiation),
           SavedInNonInstantiationSFINAEContext(false), Entity(nullptr),
           Template(nullptr), TemplateArgs(nullptr), NumTemplateArgs(0),
           DeductionInfo(nullptr) {}
 
     /// Determines whether this template is an actual instantiation
     /// that should be counted toward the maximum instantiation depth.
     bool isInstantiationRecord() const;
   };
 
   /// A stack object to be created when performing template
   /// instantiation.
   ///
   /// Construction of an object of type \c InstantiatingTemplate
   /// pushes the current instantiation onto the stack of active
   /// instantiations. If the size of this stack exceeds the maximum
   /// number of recursive template instantiations, construction
   /// produces an error and evaluates true.
   ///
   /// Destruction of this object will pop the named instantiation off
   /// the stack.
   struct InstantiatingTemplate {
     /// Note that we are instantiating a class template,
     /// function template, variable template, alias template,
     /// or a member thereof.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           Decl *Entity,
                           SourceRange InstantiationRange = SourceRange());
 
     struct ExceptionSpecification {};
     /// Note that we are instantiating an exception specification
     /// of a function template.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           FunctionDecl *Entity, ExceptionSpecification,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating a type alias template declaration.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TypeAliasTemplateDecl *Entity,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating a default argument in a
     /// template-id.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TemplateParameter Param, TemplateDecl *Template,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are substituting either explicitly-specified or
     /// deduced template arguments during function template argument deduction.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           FunctionTemplateDecl *FunctionTemplate,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           CodeSynthesisContext::SynthesisKind Kind,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating as part of template
     /// argument deduction for a class template declaration.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TemplateDecl *Template,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating as part of template
     /// argument deduction for a class template partial
     /// specialization.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ClassTemplatePartialSpecializationDecl *PartialSpec,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating as part of template
     /// argument deduction for a variable template partial
     /// specialization.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           VarTemplatePartialSpecializationDecl *PartialSpec,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are instantiating a default argument for a function
     /// parameter.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ParmVarDecl *Param,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we are substituting prior template arguments into a
     /// non-type parameter.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           NamedDecl *Template, NonTypeTemplateParmDecl *Param,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange);
 
     /// Note that we are substituting prior template arguments into a
     /// template template parameter.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           NamedDecl *Template, TemplateTemplateParmDecl *Param,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange);
 
     /// Note that we are checking the default template argument
     /// against the template parameter for a given template-id.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TemplateDecl *Template, NamedDecl *Param,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange);
 
     struct ConstraintsCheck {};
     /// \brief Note that we are checking the constraints associated with some
     /// constrained entity (a concept declaration or a template with associated
     /// constraints).
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ConstraintsCheck, NamedDecl *Template,
                           ArrayRef<TemplateArgument> TemplateArgs,
                           SourceRange InstantiationRange);
 
     struct ConstraintSubstitution {};
     /// \brief Note that we are checking a constraint expression associated
     /// with a template declaration or as part of the satisfaction check of a
     /// concept.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ConstraintSubstitution, NamedDecl *Template,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange);
 
     struct ConstraintNormalization {};
     /// \brief Note that we are normalizing a constraint expression.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ConstraintNormalization, NamedDecl *Template,
                           SourceRange InstantiationRange);
 
     struct ParameterMappingSubstitution {};
     /// \brief Note that we are subtituting into the parameter mapping of an
     /// atomic constraint during constraint normalization.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           ParameterMappingSubstitution, NamedDecl *Template,
                           SourceRange InstantiationRange);
 
     /// \brief Note that we are substituting template arguments into a part of
     /// a requirement of a requires expression.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           concepts::Requirement *Req,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange = SourceRange());
 
     /// \brief Note that we are checking the satisfaction of the constraint
     /// expression inside of a nested requirement.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           concepts::NestedRequirement *Req, ConstraintsCheck,
                           SourceRange InstantiationRange = SourceRange());
 
     /// \brief Note that we are checking a requires clause.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           const RequiresExpr *E,
                           sema::TemplateDeductionInfo &DeductionInfo,
                           SourceRange InstantiationRange);
 
     struct BuildingDeductionGuidesTag {};
     /// \brief Note that we are building deduction guides.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                           TemplateDecl *Entity, BuildingDeductionGuidesTag,
                           SourceRange InstantiationRange = SourceRange());
 
     struct PartialOrderingTTP {};
     /// \brief Note that we are partial ordering template template parameters.
     InstantiatingTemplate(Sema &SemaRef, SourceLocation ArgLoc,
                           PartialOrderingTTP, TemplateDecl *PArg,
                           SourceRange InstantiationRange = SourceRange());
 
     /// Note that we have finished instantiating this template.
     void Clear();
 
     ~InstantiatingTemplate() { Clear(); }
 
     /// Determines whether we have exceeded the maximum
     /// recursive template instantiations.
     bool isInvalid() const { return Invalid; }
 
     /// Determine whether we are already instantiating this
     /// specialization in some surrounding active instantiation.
     bool isAlreadyInstantiating() const { return AlreadyInstantiating; }
 
   private:
     Sema &SemaRef;
     bool Invalid;
     bool AlreadyInstantiating;
     bool CheckInstantiationDepth(SourceLocation PointOfInstantiation,
                                  SourceRange InstantiationRange);
 
     InstantiatingTemplate(Sema &SemaRef,
                           CodeSynthesisContext::SynthesisKind Kind,
                           SourceLocation PointOfInstantiation,
                           SourceRange InstantiationRange, Decl *Entity,
                           NamedDecl *Template = nullptr,
                           ArrayRef<TemplateArgument> TemplateArgs = {},
                           sema::TemplateDeductionInfo *DeductionInfo = nullptr);
 
     InstantiatingTemplate(const InstantiatingTemplate &) = delete;
 
     InstantiatingTemplate &operator=(const InstantiatingTemplate &) = delete;
   };
 
   bool SubstTemplateArgument(const TemplateArgumentLoc &Input,
                              const MultiLevelTemplateArgumentList &TemplateArgs,
                              TemplateArgumentLoc &Output,
                              SourceLocation Loc = {},
                              const DeclarationName &Entity = {});
   bool
   SubstTemplateArguments(ArrayRef<TemplateArgumentLoc> Args,
                          const MultiLevelTemplateArgumentList &TemplateArgs,
                          TemplateArgumentListInfo &Outputs);
 
   /// Retrieve the template argument list(s) that should be used to
   /// instantiate the definition of the given declaration.
   ///
   /// \param ND the declaration for which we are computing template
   /// instantiation arguments.
   ///
   /// \param DC In the event we don't HAVE a declaration yet, we instead provide
   ///  the decl context where it will be created.  In this case, the `Innermost`
   ///  should likely be provided.  If ND is non-null, this is ignored.
   ///
   /// \param Innermost if non-NULL, specifies a template argument list for the
   /// template declaration passed as ND.
   ///
   /// \param RelativeToPrimary true if we should get the template
   /// arguments relative to the primary template, even when we're
   /// dealing with a specialization. This is only relevant for function
   /// template specializations.
   ///
   /// \param Pattern If non-NULL, indicates the pattern from which we will be
   /// instantiating the definition of the given declaration, \p ND. This is
   /// used to determine the proper set of template instantiation arguments for
   /// friend function template specializations.
   ///
   /// \param ForConstraintInstantiation when collecting arguments,
   /// ForConstraintInstantiation indicates we should continue looking when
   /// encountering a lambda generic call operator, and continue looking for
   /// arguments on an enclosing class template.
   ///
   /// \param SkipForSpecialization when specified, any template specializations
   /// in a traversal would be ignored.
   /// \param ForDefaultArgumentSubstitution indicates we should continue looking
   /// when encountering a specialized member function template, rather than
   /// returning immediately.
   MultiLevelTemplateArgumentList getTemplateInstantiationArgs(
       const NamedDecl *D, const DeclContext *DC = nullptr, bool Final = false,
       std::optional<ArrayRef<TemplateArgument>> Innermost = std::nullopt,
       bool RelativeToPrimary = false, const FunctionDecl *Pattern = nullptr,
       bool ForConstraintInstantiation = false,
       bool SkipForSpecialization = false,
       bool ForDefaultArgumentSubstitution = false);
 
   /// RAII object to handle the state changes required to synthesize
   /// a function body.
   class SynthesizedFunctionScope {
     Sema &S;
     Sema::ContextRAII SavedContext;
     bool PushedCodeSynthesisContext = false;
 
   public:
     SynthesizedFunctionScope(Sema &S, DeclContext *DC)
         : S(S), SavedContext(S, DC) {
       auto *FD = dyn_cast<FunctionDecl>(DC);
       S.PushFunctionScope();
       S.PushExpressionEvaluationContext(
           (FD && FD->isImmediateFunction())
               ? ExpressionEvaluationContext::ImmediateFunctionContext
               : ExpressionEvaluationContext::PotentiallyEvaluated);
       if (FD) {
         auto &Current = S.currentEvaluationContext();
         const auto &Parent = S.parentEvaluationContext();
 
         FD->setWillHaveBody(true);
         Current.InImmediateFunctionContext =
             FD->isImmediateFunction() ||
             (isLambdaMethod(FD) && (Parent.isConstantEvaluated() ||
                                     Parent.isImmediateFunctionContext()));
 
         Current.InImmediateEscalatingFunctionContext =
             S.getLangOpts().CPlusPlus20 && FD->isImmediateEscalating();
       } else
         assert(isa<ObjCMethodDecl>(DC));
     }
 
     void addContextNote(SourceLocation UseLoc) {
       assert(!PushedCodeSynthesisContext);
 
       Sema::CodeSynthesisContext Ctx;
       Ctx.Kind = Sema::CodeSynthesisContext::DefiningSynthesizedFunction;
       Ctx.PointOfInstantiation = UseLoc;
       Ctx.Entity = cast<Decl>(S.CurContext);
       S.pushCodeSynthesisContext(Ctx);
 
       PushedCodeSynthesisContext = true;
     }
 
     ~SynthesizedFunctionScope() {
       if (PushedCodeSynthesisContext)
         S.popCodeSynthesisContext();
       if (auto *FD = dyn_cast<FunctionDecl>(S.CurContext)) {
         FD->setWillHaveBody(false);
         S.CheckImmediateEscalatingFunctionDefinition(FD, S.getCurFunction());
       }
       S.PopExpressionEvaluationContext();
       S.PopFunctionScopeInfo();
     }
   };
 
   /// List of active code synthesis contexts.
   ///
   /// This vector is treated as a stack. As synthesis of one entity requires
   /// synthesis of another, additional contexts are pushed onto the stack.
   SmallVector<CodeSynthesisContext, 16> CodeSynthesisContexts;
 
   /// Specializations whose definitions are currently being instantiated.
   llvm::DenseSet<std::pair<Decl *, unsigned>> InstantiatingSpecializations;
 
   /// Non-dependent types used in templates that have already been instantiated
   /// by some template instantiation.
   llvm::DenseSet<QualType> InstantiatedNonDependentTypes;
 
   /// Extra modules inspected when performing a lookup during a template
   /// instantiation. Computed lazily.
   SmallVector<Module *, 16> CodeSynthesisContextLookupModules;
 
   /// Cache of additional modules that should be used for name lookup
   /// within the current template instantiation. Computed lazily; use
   /// getLookupModules() to get a complete set.
   llvm::DenseSet<Module *> LookupModulesCache;
 
   /// Map from the most recent declaration of a namespace to the most
   /// recent visible declaration of that namespace.
   llvm::DenseMap<NamedDecl *, NamedDecl *> VisibleNamespaceCache;
 
   /// Whether we are in a SFINAE context that is not associated with
   /// template instantiation.
   ///
   /// This is used when setting up a SFINAE trap (\c see SFINAETrap) outside
   /// of a template instantiation or template argument deduction.
   bool InNonInstantiationSFINAEContext;
 
   /// The number of \p CodeSynthesisContexts that are not template
   /// instantiations and, therefore, should not be counted as part of the
   /// instantiation depth.
   ///
   /// When the instantiation depth reaches the user-configurable limit
   /// \p LangOptions::InstantiationDepth we will abort instantiation.
   // FIXME: Should we have a similar limit for other forms of synthesis?
   unsigned NonInstantiationEntries;
 
   /// The depth of the context stack at the point when the most recent
   /// error or warning was produced.
   ///
   /// This value is used to suppress printing of redundant context stacks
   /// when there are multiple errors or warnings in the same instantiation.
   // FIXME: Does this belong in Sema? It's tough to implement it anywhere else.
   unsigned LastEmittedCodeSynthesisContextDepth = 0;
 
   /// The template instantiation callbacks to trace or track
   /// instantiations (objects can be chained).
   ///
   /// This callbacks is used to print, trace or track template
   /// instantiations as they are being constructed.
   std::vector<std::unique_ptr<TemplateInstantiationCallback>>
       TemplateInstCallbacks;
 
   /// The current index into pack expansion arguments that will be
   /// used for substitution of parameter packs.
   ///
   /// The pack expansion index will be -1 to indicate that parameter packs
   /// should be instantiated as themselves. Otherwise, the index specifies
   /// which argument within the parameter pack will be used for substitution.
   int ArgumentPackSubstitutionIndex;
 
   /// RAII object used to change the argument pack substitution index
   /// within a \c Sema object.
   ///
   /// See \c ArgumentPackSubstitutionIndex for more information.
   class ArgumentPackSubstitutionIndexRAII {
     Sema &Self;
     int OldSubstitutionIndex;
 
   public:
     ArgumentPackSubstitutionIndexRAII(Sema &Self, int NewSubstitutionIndex)
         : Self(Self), OldSubstitutionIndex(Self.ArgumentPackSubstitutionIndex) {
       Self.ArgumentPackSubstitutionIndex = NewSubstitutionIndex;
     }
 
     ~ArgumentPackSubstitutionIndexRAII() {
       Self.ArgumentPackSubstitutionIndex = OldSubstitutionIndex;
     }
   };
 
   friend class ArgumentPackSubstitutionRAII;
 
   void pushCodeSynthesisContext(CodeSynthesisContext Ctx);
   void popCodeSynthesisContext();
 
   void PrintContextStack() {
     if (!CodeSynthesisContexts.empty() &&
         CodeSynthesisContexts.size() != LastEmittedCodeSynthesisContextDepth) {
       PrintInstantiationStack();
       LastEmittedCodeSynthesisContextDepth = CodeSynthesisContexts.size();
     }
     if (PragmaAttributeCurrentTargetDecl)
       PrintPragmaAttributeInstantiationPoint();
   }
   /// Prints the current instantiation stack through a series of
   /// notes.
   void PrintInstantiationStack();
 
   /// Determines whether we are currently in a context where
   /// template argument substitution failures are not considered
   /// errors.
   ///
   /// \returns An empty \c Optional if we're not in a SFINAE context.
   /// Otherwise, contains a pointer that, if non-NULL, contains the nearest
   /// template-deduction context object, which can be used to capture
   /// diagnostics that will be suppressed.
   std::optional<sema::TemplateDeductionInfo *> isSFINAEContext() const;
 
   /// Perform substitution on the type T with a given set of template
   /// arguments.
   ///
   /// This routine substitutes the given template arguments into the
   /// type T and produces the instantiated type.
   ///
   /// \param T the type into which the template arguments will be
   /// substituted. If this type is not dependent, it will be returned
   /// immediately.
   ///
   /// \param Args the template arguments that will be
   /// substituted for the top-level template parameters within T.
   ///
   /// \param Loc the location in the source code where this substitution
   /// is being performed. It will typically be the location of the
   /// declarator (if we're instantiating the type of some declaration)
   /// or the location of the type in the source code (if, e.g., we're
   /// instantiating the type of a cast expression).
   ///
   /// \param Entity the name of the entity associated with a declaration
   /// being instantiated (if any). May be empty to indicate that there
   /// is no such entity (if, e.g., this is a type that occurs as part of
   /// a cast expression) or that the entity has no name (e.g., an
   /// unnamed function parameter).
   ///
   /// \param AllowDeducedTST Whether a DeducedTemplateSpecializationType is
   /// acceptable as the top level type of the result.
   ///
   /// \param IsIncompleteSubstitution If provided, the pointee will be set
   /// whenever substitution would perform a replacement with a null or
   /// non-existent template argument.
   ///
   /// \returns If the instantiation succeeds, the instantiated
   /// type. Otherwise, produces diagnostics and returns a NULL type.
   TypeSourceInfo *SubstType(TypeSourceInfo *T,
                             const MultiLevelTemplateArgumentList &TemplateArgs,
                             SourceLocation Loc, DeclarationName Entity,
                             bool AllowDeducedTST = false);
 
   QualType SubstType(QualType T,
                      const MultiLevelTemplateArgumentList &TemplateArgs,
                      SourceLocation Loc, DeclarationName Entity,
                      bool *IsIncompleteSubstitution = nullptr);
 
   TypeSourceInfo *SubstType(TypeLoc TL,
                             const MultiLevelTemplateArgumentList &TemplateArgs,
                             SourceLocation Loc, DeclarationName Entity);
 
   /// A form of SubstType intended specifically for instantiating the
   /// type of a FunctionDecl.  Its purpose is solely to force the
   /// instantiation of default-argument expressions and to avoid
   /// instantiating an exception-specification.
   TypeSourceInfo *SubstFunctionDeclType(
       TypeSourceInfo *T, const MultiLevelTemplateArgumentList &TemplateArgs,
       SourceLocation Loc, DeclarationName Entity, CXXRecordDecl *ThisContext,
       Qualifiers ThisTypeQuals, bool EvaluateConstraints = true);
   void SubstExceptionSpec(FunctionDecl *New, const FunctionProtoType *Proto,
                           const MultiLevelTemplateArgumentList &Args);
   bool SubstExceptionSpec(SourceLocation Loc,
                           FunctionProtoType::ExceptionSpecInfo &ESI,
                           SmallVectorImpl<QualType> &ExceptionStorage,
                           const MultiLevelTemplateArgumentList &Args);
   ParmVarDecl *
   SubstParmVarDecl(ParmVarDecl *D,
                    const MultiLevelTemplateArgumentList &TemplateArgs,
                    int indexAdjustment, std::optional<unsigned> NumExpansions,
                    bool ExpectParameterPack, bool EvaluateConstraints = true);
 
   /// Substitute the given template arguments into the given set of
   /// parameters, producing the set of parameter types that would be generated
   /// from such a substitution.
   bool SubstParmTypes(SourceLocation Loc, ArrayRef<ParmVarDecl *> Params,
                       const FunctionProtoType::ExtParameterInfo *ExtParamInfos,
                       const MultiLevelTemplateArgumentList &TemplateArgs,
                       SmallVectorImpl<QualType> &ParamTypes,
                       SmallVectorImpl<ParmVarDecl *> *OutParams,
                       ExtParameterInfoBuilder &ParamInfos);
 
   /// Substitute the given template arguments into the default argument.
   bool SubstDefaultArgument(SourceLocation Loc, ParmVarDecl *Param,
                             const MultiLevelTemplateArgumentList &TemplateArgs,
                             bool ForCallExpr = false);
   ExprResult SubstExpr(Expr *E,
                        const MultiLevelTemplateArgumentList &TemplateArgs);
 
   // A RAII type used by the TemplateDeclInstantiator and TemplateInstantiator
   // to disable constraint evaluation, then restore the state.
   template <typename InstTy> struct ConstraintEvalRAII {
     InstTy &TI;
     bool OldValue;
 
     ConstraintEvalRAII(InstTy &TI)
         : TI(TI), OldValue(TI.getEvaluateConstraints()) {
       TI.setEvaluateConstraints(false);
     }
     ~ConstraintEvalRAII() { TI.setEvaluateConstraints(OldValue); }
   };
 
   // Must be used instead of SubstExpr at 'constraint checking' time.
   ExprResult
   SubstConstraintExpr(Expr *E,
                       const MultiLevelTemplateArgumentList &TemplateArgs);
   // Unlike the above, this does not evaluates constraints.
   ExprResult SubstConstraintExprWithoutSatisfaction(
       Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Substitute the given template arguments into a list of
   /// expressions, expanding pack expansions if required.
   ///
   /// \param Exprs The list of expressions to substitute into.
   ///
   /// \param IsCall Whether this is some form of call, in which case
   /// default arguments will be dropped.
   ///
   /// \param TemplateArgs The set of template arguments to substitute.
   ///
   /// \param Outputs Will receive all of the substituted arguments.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool SubstExprs(ArrayRef<Expr *> Exprs, bool IsCall,
                   const MultiLevelTemplateArgumentList &TemplateArgs,
                   SmallVectorImpl<Expr *> &Outputs);
 
   StmtResult SubstStmt(Stmt *S,
                        const MultiLevelTemplateArgumentList &TemplateArgs);
 
   ExprResult
   SubstInitializer(Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs,
                    bool CXXDirectInit);
 
   /// Perform substitution on the base class specifiers of the
   /// given class template specialization.
   ///
   /// Produces a diagnostic and returns true on error, returns false and
   /// attaches the instantiated base classes to the class template
   /// specialization if successful.
   bool SubstBaseSpecifiers(CXXRecordDecl *Instantiation, CXXRecordDecl *Pattern,
                            const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Instantiate the definition of a class from a given pattern.
   ///
   /// \param PointOfInstantiation The point of instantiation within the
   /// source code.
   ///
   /// \param Instantiation is the declaration whose definition is being
   /// instantiated. This will be either a class template specialization
   /// or a member class of a class template specialization.
   ///
   /// \param Pattern is the pattern from which the instantiation
   /// occurs. This will be either the declaration of a class template or
   /// the declaration of a member class of a class template.
   ///
   /// \param TemplateArgs The template arguments to be substituted into
   /// the pattern.
   ///
   /// \param TSK the kind of implicit or explicit instantiation to perform.
   ///
   /// \param Complain whether to complain if the class cannot be instantiated
   /// due to the lack of a definition.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool InstantiateClass(SourceLocation PointOfInstantiation,
                         CXXRecordDecl *Instantiation, CXXRecordDecl *Pattern,
                         const MultiLevelTemplateArgumentList &TemplateArgs,
                         TemplateSpecializationKind TSK, bool Complain = true);
 
   /// Instantiate the definition of an enum from a given pattern.
   ///
   /// \param PointOfInstantiation The point of instantiation within the
   ///        source code.
   /// \param Instantiation is the declaration whose definition is being
   ///        instantiated. This will be a member enumeration of a class
   ///        temploid specialization, or a local enumeration within a
   ///        function temploid specialization.
   /// \param Pattern The templated declaration from which the instantiation
   ///        occurs.
   /// \param TemplateArgs The template arguments to be substituted into
   ///        the pattern.
   /// \param TSK The kind of implicit or explicit instantiation to perform.
   ///
   /// \return \c true if an error occurred, \c false otherwise.
   bool InstantiateEnum(SourceLocation PointOfInstantiation,
                        EnumDecl *Instantiation, EnumDecl *Pattern,
                        const MultiLevelTemplateArgumentList &TemplateArgs,
                        TemplateSpecializationKind TSK);
 
   /// Instantiate the definition of a field from the given pattern.
   ///
   /// \param PointOfInstantiation The point of instantiation within the
   ///        source code.
   /// \param Instantiation is the declaration whose definition is being
   ///        instantiated. This will be a class of a class temploid
   ///        specialization, or a local enumeration within a function temploid
   ///        specialization.
   /// \param Pattern The templated declaration from which the instantiation
   ///        occurs.
   /// \param TemplateArgs The template arguments to be substituted into
   ///        the pattern.
   ///
   /// \return \c true if an error occurred, \c false otherwise.
   bool InstantiateInClassInitializer(
       SourceLocation PointOfInstantiation, FieldDecl *Instantiation,
       FieldDecl *Pattern, const MultiLevelTemplateArgumentList &TemplateArgs);
 
   bool usesPartialOrExplicitSpecialization(
       SourceLocation Loc, ClassTemplateSpecializationDecl *ClassTemplateSpec);
 
   bool InstantiateClassTemplateSpecialization(
       SourceLocation PointOfInstantiation,
       ClassTemplateSpecializationDecl *ClassTemplateSpec,
       TemplateSpecializationKind TSK, bool Complain,
       bool PrimaryHasMatchedPackOnParmToNonPackOnArg);
 
   /// Instantiates the definitions of all of the member
   /// of the given class, which is an instantiation of a class template
   /// or a member class of a template.
   void
   InstantiateClassMembers(SourceLocation PointOfInstantiation,
                           CXXRecordDecl *Instantiation,
                           const MultiLevelTemplateArgumentList &TemplateArgs,
                           TemplateSpecializationKind TSK);
 
   /// Instantiate the definitions of all of the members of the
   /// given class template specialization, which was named as part of an
   /// explicit instantiation.
   void InstantiateClassTemplateSpecializationMembers(
       SourceLocation PointOfInstantiation,
       ClassTemplateSpecializationDecl *ClassTemplateSpec,
       TemplateSpecializationKind TSK);
 
   NestedNameSpecifierLoc SubstNestedNameSpecifierLoc(
       NestedNameSpecifierLoc NNS,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Do template substitution on declaration name info.
   DeclarationNameInfo
   SubstDeclarationNameInfo(const DeclarationNameInfo &NameInfo,
                            const MultiLevelTemplateArgumentList &TemplateArgs);
   TemplateName
   SubstTemplateName(NestedNameSpecifierLoc QualifierLoc, TemplateName Name,
                     SourceLocation Loc,
                     const MultiLevelTemplateArgumentList &TemplateArgs);
 
   bool SubstTypeConstraint(TemplateTypeParmDecl *Inst, const TypeConstraint *TC,
                            const MultiLevelTemplateArgumentList &TemplateArgs,
                            bool EvaluateConstraint);
 
   /// Determine whether we are currently performing template instantiation.
   bool inTemplateInstantiation() const {
     return CodeSynthesisContexts.size() > NonInstantiationEntries;
   }
 
   using EntityPrinter = llvm::function_ref<void(llvm::raw_ostream &)>;
 
   /// \brief create a Requirement::SubstitutionDiagnostic with only a
   /// SubstitutedEntity and DiagLoc using ASTContext's allocator.
   concepts::Requirement::SubstitutionDiagnostic *
   createSubstDiagAt(SourceLocation Location, EntityPrinter Printer);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Template Declaration Instantiation
   /// Implementations are in SemaTemplateInstantiateDecl.cpp
   ///@{
 
 public:
   /// An entity for which implicit template instantiation is required.
   ///
   /// The source location associated with the declaration is the first place in
   /// the source code where the declaration was "used". It is not necessarily
   /// the point of instantiation (which will be either before or after the
   /// namespace-scope declaration that triggered this implicit instantiation),
   /// However, it is the location that diagnostics should generally refer to,
   /// because users will need to know what code triggered the instantiation.
   typedef std::pair<ValueDecl *, SourceLocation> PendingImplicitInstantiation;
 
   /// The queue of implicit template instantiations that are required
   /// but have not yet been performed.
   std::deque<PendingImplicitInstantiation> PendingInstantiations;
 
   /// Queue of implicit template instantiations that cannot be performed
   /// eagerly.
   SmallVector<PendingImplicitInstantiation, 1> LateParsedInstantiations;
 
   SmallVector<SmallVector<VTableUse, 16>, 8> SavedVTableUses;
   SmallVector<std::deque<PendingImplicitInstantiation>, 8>
       SavedPendingInstantiations;
 
   /// The queue of implicit template instantiations that are required
   /// and must be performed within the current local scope.
   ///
   /// This queue is only used for member functions of local classes in
   /// templates, which must be instantiated in the same scope as their
   /// enclosing function, so that they can reference function-local
   /// types, static variables, enumerators, etc.
   std::deque<PendingImplicitInstantiation> PendingLocalImplicitInstantiations;
 
   class LocalEagerInstantiationScope {
   public:
     LocalEagerInstantiationScope(Sema &S) : S(S) {
       SavedPendingLocalImplicitInstantiations.swap(
           S.PendingLocalImplicitInstantiations);
     }
 
     void perform() { S.PerformPendingInstantiations(/*LocalOnly=*/true); }
 
     ~LocalEagerInstantiationScope() {
       assert(S.PendingLocalImplicitInstantiations.empty() &&
              "there shouldn't be any pending local implicit instantiations");
       SavedPendingLocalImplicitInstantiations.swap(
           S.PendingLocalImplicitInstantiations);
     }
 
   private:
     Sema &S;
     std::deque<PendingImplicitInstantiation>
         SavedPendingLocalImplicitInstantiations;
   };
 
   /// Records and restores the CurFPFeatures state on entry/exit of compound
   /// statements.
   class FPFeaturesStateRAII {
   public:
     FPFeaturesStateRAII(Sema &S);
     ~FPFeaturesStateRAII();
     FPOptionsOverride getOverrides() { return OldOverrides; }
 
   private:
     Sema &S;
     FPOptions OldFPFeaturesState;
     FPOptionsOverride OldOverrides;
     LangOptions::FPEvalMethodKind OldEvalMethod;
     SourceLocation OldFPPragmaLocation;
   };
 
   class GlobalEagerInstantiationScope {
   public:
     GlobalEagerInstantiationScope(Sema &S, bool Enabled)
         : S(S), Enabled(Enabled) {
       if (!Enabled)
         return;
 
       S.SavedPendingInstantiations.emplace_back();
       S.SavedPendingInstantiations.back().swap(S.PendingInstantiations);
 
       S.SavedVTableUses.emplace_back();
       S.SavedVTableUses.back().swap(S.VTableUses);
     }
 
     void perform() {
       if (Enabled) {
         S.DefineUsedVTables();
         S.PerformPendingInstantiations();
       }
     }
 
     ~GlobalEagerInstantiationScope() {
       if (!Enabled)
         return;
 
       // Restore the set of pending vtables.
       assert(S.VTableUses.empty() &&
              "VTableUses should be empty before it is discarded.");
       S.VTableUses.swap(S.SavedVTableUses.back());
       S.SavedVTableUses.pop_back();
 
       // Restore the set of pending implicit instantiations.
       if (S.TUKind != TU_Prefix || !S.LangOpts.PCHInstantiateTemplates) {
         assert(S.PendingInstantiations.empty() &&
                "PendingInstantiations should be empty before it is discarded.");
         S.PendingInstantiations.swap(S.SavedPendingInstantiations.back());
         S.SavedPendingInstantiations.pop_back();
       } else {
         // Template instantiations in the PCH may be delayed until the TU.
         S.PendingInstantiations.swap(S.SavedPendingInstantiations.back());
         S.PendingInstantiations.insert(
             S.PendingInstantiations.end(),
             S.SavedPendingInstantiations.back().begin(),
             S.SavedPendingInstantiations.back().end());
         S.SavedPendingInstantiations.pop_back();
       }
     }
 
   private:
     Sema &S;
     bool Enabled;
   };
 
   ExplicitSpecifier instantiateExplicitSpecifier(
       const MultiLevelTemplateArgumentList &TemplateArgs, ExplicitSpecifier ES);
 
   struct LateInstantiatedAttribute {
     const Attr *TmplAttr;
     LocalInstantiationScope *Scope;
     Decl *NewDecl;
 
     LateInstantiatedAttribute(const Attr *A, LocalInstantiationScope *S,
                               Decl *D)
         : TmplAttr(A), Scope(S), NewDecl(D) {}
   };
   typedef SmallVector<LateInstantiatedAttribute, 16> LateInstantiatedAttrVec;
 
   void InstantiateAttrs(const MultiLevelTemplateArgumentList &TemplateArgs,
                         const Decl *Pattern, Decl *Inst,
                         LateInstantiatedAttrVec *LateAttrs = nullptr,
                         LocalInstantiationScope *OuterMostScope = nullptr);
 
   /// Update instantiation attributes after template was late parsed.
   ///
   /// Some attributes are evaluated based on the body of template. If it is
   /// late parsed, such attributes cannot be evaluated when declaration is
   /// instantiated. This function is used to update instantiation attributes
   /// when template definition is ready.
   void updateAttrsForLateParsedTemplate(const Decl *Pattern, Decl *Inst);
 
   void
   InstantiateAttrsForDecl(const MultiLevelTemplateArgumentList &TemplateArgs,
                           const Decl *Pattern, Decl *Inst,
                           LateInstantiatedAttrVec *LateAttrs = nullptr,
                           LocalInstantiationScope *OuterMostScope = nullptr);
 
   /// In the MS ABI, we need to instantiate default arguments of dllexported
   /// default constructors along with the constructor definition. This allows IR
   /// gen to emit a constructor closure which calls the default constructor with
   /// its default arguments.
   void InstantiateDefaultCtorDefaultArgs(CXXConstructorDecl *Ctor);
 
   bool InstantiateDefaultArgument(SourceLocation CallLoc, FunctionDecl *FD,
                                   ParmVarDecl *Param);
   void InstantiateExceptionSpec(SourceLocation PointOfInstantiation,
                                 FunctionDecl *Function);
 
   /// Instantiate (or find existing instantiation of) a function template with a
   /// given set of template arguments.
   ///
   /// Usually this should not be used, and template argument deduction should be
   /// used in its place.
   FunctionDecl *InstantiateFunctionDeclaration(
       FunctionTemplateDecl *FTD, const TemplateArgumentList *Args,
       SourceLocation Loc,
       CodeSynthesisContext::SynthesisKind CSC =
           CodeSynthesisContext::ExplicitTemplateArgumentSubstitution);
 
   /// Instantiate the definition of the given function from its
   /// template.
   ///
   /// \param PointOfInstantiation the point at which the instantiation was
   /// required. Note that this is not precisely a "point of instantiation"
   /// for the function, but it's close.
   ///
   /// \param Function the already-instantiated declaration of a
   /// function template specialization or member function of a class template
   /// specialization.
   ///
   /// \param Recursive if true, recursively instantiates any functions that
   /// are required by this instantiation.
   ///
   /// \param DefinitionRequired if true, then we are performing an explicit
   /// instantiation where the body of the function is required. Complain if
   /// there is no such body.
   void InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
                                      FunctionDecl *Function,
                                      bool Recursive = false,
                                      bool DefinitionRequired = false,
                                      bool AtEndOfTU = false);
   VarTemplateSpecializationDecl *BuildVarTemplateInstantiation(
       VarTemplateDecl *VarTemplate, VarDecl *FromVar,
       const TemplateArgumentList *PartialSpecArgs,
       const TemplateArgumentListInfo &TemplateArgsInfo,
       SmallVectorImpl<TemplateArgument> &Converted,
       SourceLocation PointOfInstantiation,
       LateInstantiatedAttrVec *LateAttrs = nullptr,
       LocalInstantiationScope *StartingScope = nullptr);
 
   /// Instantiates a variable template specialization by completing it
   /// with appropriate type information and initializer.
   VarTemplateSpecializationDecl *CompleteVarTemplateSpecializationDecl(
       VarTemplateSpecializationDecl *VarSpec, VarDecl *PatternDecl,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// BuildVariableInstantiation - Used after a new variable has been created.
   /// Sets basic variable data and decides whether to postpone the
   /// variable instantiation.
   void
   BuildVariableInstantiation(VarDecl *NewVar, VarDecl *OldVar,
                              const MultiLevelTemplateArgumentList &TemplateArgs,
                              LateInstantiatedAttrVec *LateAttrs,
                              DeclContext *Owner,
                              LocalInstantiationScope *StartingScope,
                              bool InstantiatingVarTemplate = false,
                              VarTemplateSpecializationDecl *PrevVTSD = nullptr);
 
   /// Instantiate the initializer of a variable.
   void InstantiateVariableInitializer(
       VarDecl *Var, VarDecl *OldVar,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Instantiate the definition of the given variable from its
   /// template.
   ///
   /// \param PointOfInstantiation the point at which the instantiation was
   /// required. Note that this is not precisely a "point of instantiation"
   /// for the variable, but it's close.
   ///
   /// \param Var the already-instantiated declaration of a templated variable.
   ///
   /// \param Recursive if true, recursively instantiates any functions that
   /// are required by this instantiation.
   ///
   /// \param DefinitionRequired if true, then we are performing an explicit
   /// instantiation where a definition of the variable is required. Complain
   /// if there is no such definition.
   void InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
                                      VarDecl *Var, bool Recursive = false,
                                      bool DefinitionRequired = false,
                                      bool AtEndOfTU = false);
 
   void InstantiateMemInitializers(
       CXXConstructorDecl *New, const CXXConstructorDecl *Tmpl,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Find the instantiation of the given declaration within the
   /// current instantiation.
   ///
   /// This routine is intended to be used when \p D is a declaration
   /// referenced from within a template, that needs to mapped into the
   /// corresponding declaration within an instantiation. For example,
   /// given:
   ///
   /// \code
   /// template<typename T>
   /// struct X {
   ///   enum Kind {
   ///     KnownValue = sizeof(T)
   ///   };
   ///
   ///   bool getKind() const { return KnownValue; }
   /// };
   ///
   /// template struct X<int>;
   /// \endcode
   ///
   /// In the instantiation of X<int>::getKind(), we need to map the \p
   /// EnumConstantDecl for \p KnownValue (which refers to
   /// X<T>::<Kind>::KnownValue) to its instantiation
   /// (X<int>::<Kind>::KnownValue).
   /// \p FindInstantiatedDecl performs this mapping from within the
   /// instantiation of X<int>.
   NamedDecl *
   FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
                        const MultiLevelTemplateArgumentList &TemplateArgs,
                        bool FindingInstantiatedContext = false);
 
   /// Finds the instantiation of the given declaration context
   /// within the current instantiation.
   ///
   /// \returns NULL if there was an error
   DeclContext *
   FindInstantiatedContext(SourceLocation Loc, DeclContext *DC,
                           const MultiLevelTemplateArgumentList &TemplateArgs);
 
   Decl *SubstDecl(Decl *D, DeclContext *Owner,
                   const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Substitute the name and return type of a defaulted 'operator<=>' to form
   /// an implicit 'operator=='.
   FunctionDecl *SubstSpaceshipAsEqualEqual(CXXRecordDecl *RD,
                                            FunctionDecl *Spaceship);
 
   /// Performs template instantiation for all implicit template
   /// instantiations we have seen until this point.
   void PerformPendingInstantiations(bool LocalOnly = false);
 
   TemplateParameterList *
   SubstTemplateParams(TemplateParameterList *Params, DeclContext *Owner,
                       const MultiLevelTemplateArgumentList &TemplateArgs,
                       bool EvaluateConstraints = true);
 
   void PerformDependentDiagnostics(
       const DeclContext *Pattern,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
 private:
   /// Introduce the instantiated local variables into the local
   /// instantiation scope.
   void addInstantiatedLocalVarsToScope(FunctionDecl *Function,
                                        const FunctionDecl *PatternDecl,
                                        LocalInstantiationScope &Scope);
   /// Introduce the instantiated function parameters into the local
   /// instantiation scope, and set the parameter names to those used
   /// in the template.
   bool addInstantiatedParametersToScope(
       FunctionDecl *Function, const FunctionDecl *PatternDecl,
       LocalInstantiationScope &Scope,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Introduce the instantiated captures of the lambda into the local
   /// instantiation scope.
   bool addInstantiatedCapturesToScope(
       FunctionDecl *Function, const FunctionDecl *PatternDecl,
       LocalInstantiationScope &Scope,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   int ParsingClassDepth = 0;
 
   class SavePendingParsedClassStateRAII {
   public:
     SavePendingParsedClassStateRAII(Sema &S) : S(S) { swapSavedState(); }
 
     ~SavePendingParsedClassStateRAII() {
       assert(S.DelayedOverridingExceptionSpecChecks.empty() &&
              "there shouldn't be any pending delayed exception spec checks");
       assert(S.DelayedEquivalentExceptionSpecChecks.empty() &&
              "there shouldn't be any pending delayed exception spec checks");
       swapSavedState();
     }
 
   private:
     Sema &S;
     decltype(DelayedOverridingExceptionSpecChecks)
         SavedOverridingExceptionSpecChecks;
     decltype(DelayedEquivalentExceptionSpecChecks)
         SavedEquivalentExceptionSpecChecks;
 
     void swapSavedState() {
       SavedOverridingExceptionSpecChecks.swap(
           S.DelayedOverridingExceptionSpecChecks);
       SavedEquivalentExceptionSpecChecks.swap(
           S.DelayedEquivalentExceptionSpecChecks);
     }
   };
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name C++ Variadic Templates
   /// Implementations are in SemaTemplateVariadic.cpp
   ///@{
 
 public:
   /// Determine whether an unexpanded parameter pack might be permitted in this
   /// location. Useful for error recovery.
   bool isUnexpandedParameterPackPermitted();
 
   /// The context in which an unexpanded parameter pack is
   /// being diagnosed.
   ///
   /// Note that the values of this enumeration line up with the first
   /// argument to the \c err_unexpanded_parameter_pack diagnostic.
   enum UnexpandedParameterPackContext {
     /// An arbitrary expression.
     UPPC_Expression = 0,
 
     /// The base type of a class type.
     UPPC_BaseType,
 
     /// The type of an arbitrary declaration.
     UPPC_DeclarationType,
 
     /// The type of a data member.
     UPPC_DataMemberType,
 
     /// The size of a bit-field.
     UPPC_BitFieldWidth,
 
     /// The expression in a static assertion.
     UPPC_StaticAssertExpression,
 
     /// The fixed underlying type of an enumeration.
     UPPC_FixedUnderlyingType,
 
     /// The enumerator value.
     UPPC_EnumeratorValue,
 
     /// A using declaration.
     UPPC_UsingDeclaration,
 
     /// A friend declaration.
     UPPC_FriendDeclaration,
 
     /// A declaration qualifier.
     UPPC_DeclarationQualifier,
 
     /// An initializer.
     UPPC_Initializer,
 
     /// A default argument.
     UPPC_DefaultArgument,
 
     /// The type of a non-type template parameter.
     UPPC_NonTypeTemplateParameterType,
 
     /// The type of an exception.
     UPPC_ExceptionType,
 
     /// Explicit specialization.
     UPPC_ExplicitSpecialization,
 
     /// Partial specialization.
     UPPC_PartialSpecialization,
 
     /// Microsoft __if_exists.
     UPPC_IfExists,
 
     /// Microsoft __if_not_exists.
     UPPC_IfNotExists,
 
     /// Lambda expression.
     UPPC_Lambda,
 
     /// Block expression.
     UPPC_Block,
 
     /// A type constraint.
     UPPC_TypeConstraint,
 
     // A requirement in a requires-expression.
     UPPC_Requirement,
 
     // A requires-clause.
     UPPC_RequiresClause,
   };
 
   /// Diagnose unexpanded parameter packs.
   ///
   /// \param Loc The location at which we should emit the diagnostic.
   ///
   /// \param UPPC The context in which we are diagnosing unexpanded
   /// parameter packs.
   ///
   /// \param Unexpanded the set of unexpanded parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPacks(
       SourceLocation Loc, UnexpandedParameterPackContext UPPC,
       ArrayRef<UnexpandedParameterPack> Unexpanded);
 
   /// If the given type contains an unexpanded parameter pack,
   /// diagnose the error.
   ///
   /// \param Loc The source location where a diagnostc should be emitted.
   ///
   /// \param T The type that is being checked for unexpanded parameter
   /// packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(SourceLocation Loc, TypeSourceInfo *T,
                                        UnexpandedParameterPackContext UPPC);
 
   /// If the given expression contains an unexpanded parameter
   /// pack, diagnose the error.
   ///
   /// \param E The expression that is being checked for unexpanded
   /// parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(
       Expr *E, UnexpandedParameterPackContext UPPC = UPPC_Expression);
 
   /// If the given requirees-expression contains an unexpanded reference to one
   /// of its own parameter packs, diagnose the error.
   ///
   /// \param RE The requiress-expression that is being checked for unexpanded
   /// parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPackInRequiresExpr(RequiresExpr *RE);
 
   /// If the given nested-name-specifier contains an unexpanded
   /// parameter pack, diagnose the error.
   ///
   /// \param SS The nested-name-specifier that is being checked for
   /// unexpanded parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(const CXXScopeSpec &SS,
                                        UnexpandedParameterPackContext UPPC);
 
   /// If the given name contains an unexpanded parameter pack,
   /// diagnose the error.
   ///
   /// \param NameInfo The name (with source location information) that
   /// is being checked for unexpanded parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(const DeclarationNameInfo &NameInfo,
                                        UnexpandedParameterPackContext UPPC);
 
   /// If the given template name contains an unexpanded parameter pack,
   /// diagnose the error.
   ///
   /// \param Loc The location of the template name.
   ///
   /// \param Template The template name that is being checked for unexpanded
   /// parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(SourceLocation Loc,
                                        TemplateName Template,
                                        UnexpandedParameterPackContext UPPC);
 
   /// If the given template argument contains an unexpanded parameter
   /// pack, diagnose the error.
   ///
   /// \param Arg The template argument that is being checked for unexpanded
   /// parameter packs.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool DiagnoseUnexpandedParameterPack(TemplateArgumentLoc Arg,
                                        UnexpandedParameterPackContext UPPC);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// template argument.
   ///
   /// \param Arg The template argument that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       TemplateArgument Arg,
       SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// template argument.
   ///
   /// \param Arg The template argument that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       TemplateArgumentLoc Arg,
       SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// type.
   ///
   /// \param T The type that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       QualType T, SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// type.
   ///
   /// \param TL The type that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       TypeLoc TL, SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// nested-name-specifier.
   ///
   /// \param NNS The nested-name-specifier that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       NestedNameSpecifierLoc NNS,
       SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// name.
   ///
   /// \param NameInfo The name that will be traversed to find
   /// unexpanded parameter packs.
   void collectUnexpandedParameterPacks(
       const DeclarationNameInfo &NameInfo,
       SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Collect the set of unexpanded parameter packs within the given
   /// expression.
   static void collectUnexpandedParameterPacks(
       Expr *E, SmallVectorImpl<UnexpandedParameterPack> &Unexpanded);
 
   /// Invoked when parsing a template argument followed by an
   /// ellipsis, which creates a pack expansion.
   ///
   /// \param Arg The template argument preceding the ellipsis, which
   /// may already be invalid.
   ///
   /// \param EllipsisLoc The location of the ellipsis.
   ParsedTemplateArgument ActOnPackExpansion(const ParsedTemplateArgument &Arg,
                                             SourceLocation EllipsisLoc);
 
   /// Invoked when parsing a type followed by an ellipsis, which
   /// creates a pack expansion.
   ///
   /// \param Type The type preceding the ellipsis, which will become
   /// the pattern of the pack expansion.
   ///
   /// \param EllipsisLoc The location of the ellipsis.
   TypeResult ActOnPackExpansion(ParsedType Type, SourceLocation EllipsisLoc);
 
   /// Construct a pack expansion type from the pattern of the pack
   /// expansion.
   TypeSourceInfo *CheckPackExpansion(TypeSourceInfo *Pattern,
                                      SourceLocation EllipsisLoc,
                                      std::optional<unsigned> NumExpansions);
 
   /// Construct a pack expansion type from the pattern of the pack
   /// expansion.
   QualType CheckPackExpansion(QualType Pattern, SourceRange PatternRange,
                               SourceLocation EllipsisLoc,
                               std::optional<unsigned> NumExpansions);
 
   /// Invoked when parsing an expression followed by an ellipsis, which
   /// creates a pack expansion.
   ///
   /// \param Pattern The expression preceding the ellipsis, which will become
   /// the pattern of the pack expansion.
   ///
   /// \param EllipsisLoc The location of the ellipsis.
   ExprResult ActOnPackExpansion(Expr *Pattern, SourceLocation EllipsisLoc);
 
   /// Invoked when parsing an expression followed by an ellipsis, which
   /// creates a pack expansion.
   ///
   /// \param Pattern The expression preceding the ellipsis, which will become
   /// the pattern of the pack expansion.
   ///
   /// \param EllipsisLoc The location of the ellipsis.
   ExprResult CheckPackExpansion(Expr *Pattern, SourceLocation EllipsisLoc,
                                 std::optional<unsigned> NumExpansions);
 
   /// Determine whether we could expand a pack expansion with the
   /// given set of parameter packs into separate arguments by repeatedly
   /// transforming the pattern.
   ///
   /// \param EllipsisLoc The location of the ellipsis that identifies the
   /// pack expansion.
   ///
   /// \param PatternRange The source range that covers the entire pattern of
   /// the pack expansion.
   ///
   /// \param Unexpanded The set of unexpanded parameter packs within the
   /// pattern.
   ///
   /// \param ShouldExpand Will be set to \c true if the transformer should
   /// expand the corresponding pack expansions into separate arguments. When
   /// set, \c NumExpansions must also be set.
   ///
   /// \param RetainExpansion Whether the caller should add an unexpanded
   /// pack expansion after all of the expanded arguments. This is used
   /// when extending explicitly-specified template argument packs per
   /// C++0x [temp.arg.explicit]p9.
   ///
   /// \param NumExpansions The number of separate arguments that will be in
   /// the expanded form of the corresponding pack expansion. This is both an
   /// input and an output parameter, which can be set by the caller if the
   /// number of expansions is known a priori (e.g., due to a prior substitution)
   /// and will be set by the callee when the number of expansions is known.
   /// The callee must set this value when \c ShouldExpand is \c true; it may
   /// set this value in other cases.
   ///
   /// \returns true if an error occurred (e.g., because the parameter packs
   /// are to be instantiated with arguments of different lengths), false
   /// otherwise. If false, \c ShouldExpand (and possibly \c NumExpansions)
   /// must be set.
   bool CheckParameterPacksForExpansion(
       SourceLocation EllipsisLoc, SourceRange PatternRange,
       ArrayRef<UnexpandedParameterPack> Unexpanded,
       const MultiLevelTemplateArgumentList &TemplateArgs, bool &ShouldExpand,
       bool &RetainExpansion, std::optional<unsigned> &NumExpansions);
 
   /// Determine the number of arguments in the given pack expansion
   /// type.
   ///
   /// This routine assumes that the number of arguments in the expansion is
   /// consistent across all of the unexpanded parameter packs in its pattern.
   ///
   /// Returns an empty Optional if the type can't be expanded.
   std::optional<unsigned> getNumArgumentsInExpansion(
       QualType T, const MultiLevelTemplateArgumentList &TemplateArgs);
 
   std::optional<unsigned> getNumArgumentsInExpansionFromUnexpanded(
       llvm::ArrayRef<UnexpandedParameterPack> Unexpanded,
       const MultiLevelTemplateArgumentList &TemplateArgs);
 
   /// Determine whether the given declarator contains any unexpanded
   /// parameter packs.
   ///
   /// This routine is used by the parser to disambiguate function declarators
   /// with an ellipsis prior to the ')', e.g.,
   ///
   /// \code
   ///   void f(T...);
   /// \endcode
   ///
   /// To determine whether we have an (unnamed) function parameter pack or
   /// a variadic function.
   ///
   /// \returns true if the declarator contains any unexpanded parameter packs,
   /// false otherwise.
   bool containsUnexpandedParameterPacks(Declarator &D);
 
   /// Returns the pattern of the pack expansion for a template argument.
   ///
   /// \param OrigLoc The template argument to expand.
   ///
   /// \param Ellipsis Will be set to the location of the ellipsis.
   ///
   /// \param NumExpansions Will be set to the number of expansions that will
   /// be generated from this pack expansion, if known a priori.
   TemplateArgumentLoc getTemplateArgumentPackExpansionPattern(
       TemplateArgumentLoc OrigLoc, SourceLocation &Ellipsis,
       std::optional<unsigned> &NumExpansions) const;
 
   /// Given a template argument that contains an unexpanded parameter pack, but
   /// which has already been substituted, attempt to determine the number of
   /// elements that will be produced once this argument is fully-expanded.
   ///
   /// This is intended for use when transforming 'sizeof...(Arg)' in order to
   /// avoid actually expanding the pack where possible.
   std::optional<unsigned> getFullyPackExpandedSize(TemplateArgument Arg);
 
   /// Called when an expression computing the size of a parameter pack
   /// is parsed.
   ///
   /// \code
   /// template<typename ...Types> struct count {
   ///   static const unsigned value = sizeof...(Types);
   /// };
   /// \endcode
   ///
   //
   /// \param OpLoc The location of the "sizeof" keyword.
   /// \param Name The name of the parameter pack whose size will be determined.
   /// \param NameLoc The source location of the name of the parameter pack.
   /// \param RParenLoc The location of the closing parentheses.
   ExprResult ActOnSizeofParameterPackExpr(Scope *S, SourceLocation OpLoc,
                                           IdentifierInfo &Name,
                                           SourceLocation NameLoc,
                                           SourceLocation RParenLoc);
 
   ExprResult ActOnPackIndexingExpr(Scope *S, Expr *PackExpression,
                                    SourceLocation EllipsisLoc,
                                    SourceLocation LSquareLoc, Expr *IndexExpr,
                                    SourceLocation RSquareLoc);
 
   ExprResult BuildPackIndexingExpr(Expr *PackExpression,
                                    SourceLocation EllipsisLoc, Expr *IndexExpr,
                                    SourceLocation RSquareLoc,
                                    ArrayRef<Expr *> ExpandedExprs = {},
                                    bool FullySubstituted = false);
 
   /// Handle a C++1z fold-expression: ( expr op ... op expr ).
   ExprResult ActOnCXXFoldExpr(Scope *S, SourceLocation LParenLoc, Expr *LHS,
                               tok::TokenKind Operator,
                               SourceLocation EllipsisLoc, Expr *RHS,
                               SourceLocation RParenLoc);
   ExprResult BuildCXXFoldExpr(UnresolvedLookupExpr *Callee,
                               SourceLocation LParenLoc, Expr *LHS,
                               BinaryOperatorKind Operator,
                               SourceLocation EllipsisLoc, Expr *RHS,
                               SourceLocation RParenLoc,
                               std::optional<unsigned> NumExpansions);
   ExprResult BuildEmptyCXXFoldExpr(SourceLocation EllipsisLoc,
                                    BinaryOperatorKind Operator);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Constraints and Concepts
   /// Implementations are in SemaConcept.cpp
   ///@{
 
 public:
   void PushSatisfactionStackEntry(const NamedDecl *D,
                                   const llvm::FoldingSetNodeID &ID) {
     const NamedDecl *Can = cast<NamedDecl>(D->getCanonicalDecl());
     SatisfactionStack.emplace_back(Can, ID);
   }
 
   void PopSatisfactionStackEntry() { SatisfactionStack.pop_back(); }
 
   bool SatisfactionStackContains(const NamedDecl *D,
                                  const llvm::FoldingSetNodeID &ID) const {
     const NamedDecl *Can = cast<NamedDecl>(D->getCanonicalDecl());
     return llvm::find(SatisfactionStack, SatisfactionStackEntryTy{Can, ID}) !=
            SatisfactionStack.end();
   }
 
   using SatisfactionStackEntryTy =
       std::pair<const NamedDecl *, llvm::FoldingSetNodeID>;
 
   // Resets the current SatisfactionStack for cases where we are instantiating
   // constraints as a 'side effect' of normal instantiation in a way that is not
   // indicative of recursive definition.
   class SatisfactionStackResetRAII {
     llvm::SmallVector<SatisfactionStackEntryTy, 10> BackupSatisfactionStack;
     Sema &SemaRef;
 
   public:
     SatisfactionStackResetRAII(Sema &S) : SemaRef(S) {
       SemaRef.SwapSatisfactionStack(BackupSatisfactionStack);
     }
 
     ~SatisfactionStackResetRAII() {
       SemaRef.SwapSatisfactionStack(BackupSatisfactionStack);
     }
   };
 
   void SwapSatisfactionStack(
       llvm::SmallVectorImpl<SatisfactionStackEntryTy> &NewSS) {
     SatisfactionStack.swap(NewSS);
   }
 
   /// Check whether the given expression is a valid constraint expression.
   /// A diagnostic is emitted if it is not, false is returned, and
   /// PossibleNonPrimary will be set to true if the failure might be due to a
   /// non-primary expression being used as an atomic constraint.
   bool CheckConstraintExpression(const Expr *CE, Token NextToken = Token(),
                                  bool *PossibleNonPrimary = nullptr,
                                  bool IsTrailingRequiresClause = false);
 
   /// \brief Check whether the given list of constraint expressions are
   /// satisfied (as if in a 'conjunction') given template arguments.
   /// \param Template the template-like entity that triggered the constraints
   /// check (either a concept or a constrained entity).
   /// \param ConstraintExprs a list of constraint expressions, treated as if
   /// they were 'AND'ed together.
   /// \param TemplateArgLists the list of template arguments to substitute into
   /// the constraint expression.
   /// \param TemplateIDRange The source range of the template id that
   /// caused the constraints check.
   /// \param Satisfaction if true is returned, will contain details of the
   /// satisfaction, with enough information to diagnose an unsatisfied
   /// expression.
   /// \returns true if an error occurred and satisfaction could not be checked,
   /// false otherwise.
   bool CheckConstraintSatisfaction(
       const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
       const MultiLevelTemplateArgumentList &TemplateArgLists,
       SourceRange TemplateIDRange, ConstraintSatisfaction &Satisfaction) {
     llvm::SmallVector<Expr *, 4> Converted;
     return CheckConstraintSatisfaction(Template, ConstraintExprs, Converted,
                                        TemplateArgLists, TemplateIDRange,
                                        Satisfaction);
   }
 
   /// \brief Check whether the given list of constraint expressions are
   /// satisfied (as if in a 'conjunction') given template arguments.
   /// Additionally, takes an empty list of Expressions which is populated with
   /// the instantiated versions of the ConstraintExprs.
   /// \param Template the template-like entity that triggered the constraints
   /// check (either a concept or a constrained entity).
   /// \param ConstraintExprs a list of constraint expressions, treated as if
   /// they were 'AND'ed together.
   /// \param ConvertedConstraints a out parameter that will get populated with
   /// the instantiated version of the ConstraintExprs if we successfully checked
   /// satisfaction.
   /// \param TemplateArgList the multi-level list of template arguments to
   /// substitute into the constraint expression. This should be relative to the
   /// top-level (hence multi-level), since we need to instantiate fully at the
   /// time of checking.
   /// \param TemplateIDRange The source range of the template id that
   /// caused the constraints check.
   /// \param Satisfaction if true is returned, will contain details of the
   /// satisfaction, with enough information to diagnose an unsatisfied
   /// expression.
   /// \returns true if an error occurred and satisfaction could not be checked,
   /// false otherwise.
   bool CheckConstraintSatisfaction(
       const NamedDecl *Template, ArrayRef<const Expr *> ConstraintExprs,
       llvm::SmallVectorImpl<Expr *> &ConvertedConstraints,
       const MultiLevelTemplateArgumentList &TemplateArgList,
       SourceRange TemplateIDRange, ConstraintSatisfaction &Satisfaction);
 
   /// \brief Check whether the given non-dependent constraint expression is
   /// satisfied. Returns false and updates Satisfaction with the satisfaction
   /// verdict if successful, emits a diagnostic and returns true if an error
   /// occurred and satisfaction could not be determined.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CheckConstraintSatisfaction(const Expr *ConstraintExpr,
                                    ConstraintSatisfaction &Satisfaction);
 
   /// Check whether the given function decl's trailing requires clause is
   /// satisfied, if any. Returns false and updates Satisfaction with the
   /// satisfaction verdict if successful, emits a diagnostic and returns true if
   /// an error occurred and satisfaction could not be determined.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool CheckFunctionConstraints(const FunctionDecl *FD,
                                 ConstraintSatisfaction &Satisfaction,
                                 SourceLocation UsageLoc = SourceLocation(),
                                 bool ForOverloadResolution = false);
 
   // Calculates whether two constraint expressions are equal irrespective of a
   // difference in 'depth'. This takes a pair of optional 'NamedDecl's 'Old' and
   // 'New', which are the "source" of the constraint, since this is necessary
   // for figuring out the relative 'depth' of the constraint. The depth of the
   // 'primary template' and the 'instantiated from' templates aren't necessarily
   // the same, such as a case when one is a 'friend' defined in a class.
   bool AreConstraintExpressionsEqual(const NamedDecl *Old,
                                      const Expr *OldConstr,
                                      const TemplateCompareNewDeclInfo &New,
                                      const Expr *NewConstr);
 
   // Calculates whether the friend function depends on an enclosing template for
   // the purposes of [temp.friend] p9.
   bool FriendConstraintsDependOnEnclosingTemplate(const FunctionDecl *FD);
 
   /// \brief Ensure that the given template arguments satisfy the constraints
   /// associated with the given template, emitting a diagnostic if they do not.
   ///
   /// \param Template The template to which the template arguments are being
   /// provided.
   ///
   /// \param TemplateArgs The converted, canonicalized template arguments.
   ///
   /// \param TemplateIDRange The source range of the template id that
   /// caused the constraints check.
   ///
   /// \returns true if the constrains are not satisfied or could not be checked
   /// for satisfaction, false if the constraints are satisfied.
   bool EnsureTemplateArgumentListConstraints(
       TemplateDecl *Template,
       const MultiLevelTemplateArgumentList &TemplateArgs,
       SourceRange TemplateIDRange);
 
   bool CheckInstantiatedFunctionTemplateConstraints(
       SourceLocation PointOfInstantiation, FunctionDecl *Decl,
       ArrayRef<TemplateArgument> TemplateArgs,
       ConstraintSatisfaction &Satisfaction);
 
   /// \brief Emit diagnostics explaining why a constraint expression was deemed
   /// unsatisfied.
   /// \param First whether this is the first time an unsatisfied constraint is
   /// diagnosed for this error.
   void DiagnoseUnsatisfiedConstraint(const ConstraintSatisfaction &Satisfaction,
                                      bool First = true);
 
   /// \brief Emit diagnostics explaining why a constraint expression was deemed
   /// unsatisfied.
   void
   DiagnoseUnsatisfiedConstraint(const ASTConstraintSatisfaction &Satisfaction,
                                 bool First = true);
 
   const NormalizedConstraint *getNormalizedAssociatedConstraints(
       NamedDecl *ConstrainedDecl, ArrayRef<const Expr *> AssociatedConstraints);
 
   /// \brief Check whether the given declaration's associated constraints are
   /// at least as constrained than another declaration's according to the
   /// partial ordering of constraints.
   ///
   /// \param Result If no error occurred, receives the result of true if D1 is
   /// at least constrained than D2, and false otherwise.
   ///
   /// \returns true if an error occurred, false otherwise.
   bool IsAtLeastAsConstrained(NamedDecl *D1, MutableArrayRef<const Expr *> AC1,
                               NamedDecl *D2, MutableArrayRef<const Expr *> AC2,
                               bool &Result);
 
   /// If D1 was not at least as constrained as D2, but would've been if a pair
   /// of atomic constraints involved had been declared in a concept and not
   /// repeated in two separate places in code.
   /// \returns true if such a diagnostic was emitted, false otherwise.
   bool MaybeEmitAmbiguousAtomicConstraintsDiagnostic(
       NamedDecl *D1, ArrayRef<const Expr *> AC1, NamedDecl *D2,
       ArrayRef<const Expr *> AC2);
 
 private:
   /// Caches pairs of template-like decls whose associated constraints were
   /// checked for subsumption and whether or not the first's constraints did in
   /// fact subsume the second's.
   llvm::DenseMap<std::pair<NamedDecl *, NamedDecl *>, bool> SubsumptionCache;
   /// Caches the normalized associated constraints of declarations (concepts or
   /// constrained declarations). If an error occurred while normalizing the
   /// associated constraints of the template or concept, nullptr will be cached
   /// here.
   llvm::DenseMap<NamedDecl *, NormalizedConstraint *> NormalizationCache;
 
   llvm::ContextualFoldingSet<ConstraintSatisfaction, const ASTContext &>
       SatisfactionCache;
 
   // The current stack of constraint satisfactions, so we can exit-early.
   llvm::SmallVector<SatisfactionStackEntryTy, 10> SatisfactionStack;
 
   /// Used by SetupConstraintCheckingTemplateArgumentsAndScope to set up the
   /// LocalInstantiationScope of the current non-lambda function. For lambdas,
   /// use LambdaScopeForCallOperatorInstantiationRAII.
   bool
   SetupConstraintScope(FunctionDecl *FD,
                        std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
                        const MultiLevelTemplateArgumentList &MLTAL,
                        LocalInstantiationScope &Scope);
 
   /// Used during constraint checking, sets up the constraint template argument
   /// lists, and calls SetupConstraintScope to set up the
   /// LocalInstantiationScope to have the proper set of ParVarDecls configured.
   std::optional<MultiLevelTemplateArgumentList>
   SetupConstraintCheckingTemplateArgumentsAndScope(
       FunctionDecl *FD, std::optional<ArrayRef<TemplateArgument>> TemplateArgs,
       LocalInstantiationScope &Scope);
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Types
   /// Implementations are in SemaType.cpp
   ///@{
 
 public:
   /// A mapping that describes the nullability we've seen in each header file.
   FileNullabilityMap NullabilityMap;
 
   static int getPrintable(int I) { return I; }
   static unsigned getPrintable(unsigned I) { return I; }
   static bool getPrintable(bool B) { return B; }
   static const char *getPrintable(const char *S) { return S; }
   static StringRef getPrintable(StringRef S) { return S; }
   static const std::string &getPrintable(const std::string &S) { return S; }
   static const IdentifierInfo *getPrintable(const IdentifierInfo *II) {
     return II;
   }
   static DeclarationName getPrintable(DeclarationName N) { return N; }
   static QualType getPrintable(QualType T) { return T; }
   static SourceRange getPrintable(SourceRange R) { return R; }
   static SourceRange getPrintable(SourceLocation L) { return L; }
   static SourceRange getPrintable(const Expr *E) { return E->getSourceRange(); }
   static SourceRange getPrintable(TypeLoc TL) { return TL.getSourceRange(); }
 
   enum class CompleteTypeKind {
     /// Apply the normal rules for complete types.  In particular,
     /// treat all sizeless types as incomplete.
     Normal,
 
     /// Relax the normal rules for complete types so that they include
     /// sizeless built-in types.
     AcceptSizeless,
 
     // FIXME: Eventually we should flip the default to Normal and opt in
     // to AcceptSizeless rather than opt out of it.
     Default = AcceptSizeless
   };
 
   QualType BuildQualifiedType(QualType T, SourceLocation Loc, Qualifiers Qs,
                               const DeclSpec *DS = nullptr);
   QualType BuildQualifiedType(QualType T, SourceLocation Loc, unsigned CVRA,
                               const DeclSpec *DS = nullptr);
 
   /// Build a pointer type.
   ///
   /// \param T The type to which we'll be building a pointer.
   ///
   /// \param Loc The location of the entity whose type involves this
   /// pointer type or, if there is no such entity, the location of the
   /// type that will have pointer type.
   ///
   /// \param Entity The name of the entity that involves the pointer
   /// type, if known.
   ///
   /// \returns A suitable pointer type, if there are no
   /// errors. Otherwise, returns a NULL type.
   QualType BuildPointerType(QualType T, SourceLocation Loc,
                             DeclarationName Entity);
 
   /// Build a reference type.
   ///
   /// \param T The type to which we'll be building a reference.
   ///
   /// \param Loc The location of the entity whose type involves this
   /// reference type or, if there is no such entity, the location of the
   /// type that will have reference type.
   ///
   /// \param Entity The name of the entity that involves the reference
   /// type, if known.
   ///
   /// \returns A suitable reference type, if there are no
   /// errors. Otherwise, returns a NULL type.
   QualType BuildReferenceType(QualType T, bool LValueRef, SourceLocation Loc,
                               DeclarationName Entity);
 
   /// Build an array type.
   ///
   /// \param T The type of each element in the array.
   ///
   /// \param ASM C99 array size modifier (e.g., '*', 'static').
   ///
   /// \param ArraySize Expression describing the size of the array.
   ///
   /// \param Brackets The range from the opening '[' to the closing ']'.
   ///
   /// \param Entity The name of the entity that involves the array
   /// type, if known.
   ///
   /// \returns A suitable array type, if there are no errors. Otherwise,
   /// returns a NULL type.
   QualType BuildArrayType(QualType T, ArraySizeModifier ASM, Expr *ArraySize,
                           unsigned Quals, SourceRange Brackets,
                           DeclarationName Entity);
   QualType BuildVectorType(QualType T, Expr *VecSize, SourceLocation AttrLoc);
 
   /// Build an ext-vector type.
   ///
   /// Run the required checks for the extended vector type.
   QualType BuildExtVectorType(QualType T, Expr *ArraySize,
                               SourceLocation AttrLoc);
   QualType BuildMatrixType(QualType T, Expr *NumRows, Expr *NumColumns,
                            SourceLocation AttrLoc);
 
   QualType BuildCountAttributedArrayOrPointerType(QualType WrappedTy,
                                                   Expr *CountExpr,
                                                   bool CountInBytes,
                                                   bool OrNull);
 
   /// BuildAddressSpaceAttr - Builds a DependentAddressSpaceType if an
   /// expression is uninstantiated. If instantiated it will apply the
   /// appropriate address space to the type. This function allows dependent
   /// template variables to be used in conjunction with the address_space
   /// attribute
   QualType BuildAddressSpaceAttr(QualType &T, LangAS ASIdx, Expr *AddrSpace,
                                  SourceLocation AttrLoc);
 
   /// Same as above, but constructs the AddressSpace index if not provided.
   QualType BuildAddressSpaceAttr(QualType &T, Expr *AddrSpace,
                                  SourceLocation AttrLoc);
 
   bool CheckQualifiedFunctionForTypeId(QualType T, SourceLocation Loc);
 
   bool CheckFunctionReturnType(QualType T, SourceLocation Loc);
 
   /// Build a function type.
   ///
   /// This routine checks the function type according to C++ rules and
   /// under the assumption that the result type and parameter types have
   /// just been instantiated from a template. It therefore duplicates
   /// some of the behavior of GetTypeForDeclarator, but in a much
   /// simpler form that is only suitable for this narrow use case.
   ///
   /// \param T The return type of the function.
   ///
   /// \param ParamTypes The parameter types of the function. This array
   /// will be modified to account for adjustments to the types of the
   /// function parameters.
   ///
   /// \param Loc The location of the entity whose type involves this
   /// function type or, if there is no such entity, the location of the
   /// type that will have function type.
   ///
   /// \param Entity The name of the entity that involves the function
   /// type, if known.
   ///
   /// \param EPI Extra information about the function type. Usually this will
   /// be taken from an existing function with the same prototype.
   ///
   /// \returns A suitable function type, if there are no errors. The
   /// unqualified type will always be a FunctionProtoType.
   /// Otherwise, returns a NULL type.
   QualType BuildFunctionType(QualType T, MutableArrayRef<QualType> ParamTypes,
                              SourceLocation Loc, DeclarationName Entity,
                              const FunctionProtoType::ExtProtoInfo &EPI);
 
   /// Build a member pointer type \c T Class::*.
   ///
   /// \param T the type to which the member pointer refers.
   /// \param Class the class type into which the member pointer points.
   /// \param Loc the location where this type begins
   /// \param Entity the name of the entity that will have this member pointer
   /// type
   ///
   /// \returns a member pointer type, if successful, or a NULL type if there was
   /// an error.
   QualType BuildMemberPointerType(QualType T, QualType Class,
                                   SourceLocation Loc, DeclarationName Entity);
 
   /// Build a block pointer type.
   ///
   /// \param T The type to which we'll be building a block pointer.
   ///
   /// \param Loc The source location, used for diagnostics.
   ///
   /// \param Entity The name of the entity that involves the block pointer
   /// type, if known.
   ///
   /// \returns A suitable block pointer type, if there are no
   /// errors. Otherwise, returns a NULL type.
   QualType BuildBlockPointerType(QualType T, SourceLocation Loc,
                                  DeclarationName Entity);
 
   /// Build a paren type including \p T.
   QualType BuildParenType(QualType T);
   QualType BuildAtomicType(QualType T, SourceLocation Loc);
 
   /// Build a Read-only Pipe type.
   ///
   /// \param T The type to which we'll be building a Pipe.
   ///
   /// \param Loc We do not use it for now.
   ///
   /// \returns A suitable pipe type, if there are no errors. Otherwise, returns
   /// a NULL type.
   QualType BuildReadPipeType(QualType T, SourceLocation Loc);
 
   /// Build a Write-only Pipe type.
   ///
   /// \param T The type to which we'll be building a Pipe.
   ///
   /// \param Loc We do not use it for now.
   ///
   /// \returns A suitable pipe type, if there are no errors. Otherwise, returns
   /// a NULL type.
   QualType BuildWritePipeType(QualType T, SourceLocation Loc);
 
   /// Build a bit-precise integer type.
   ///
   /// \param IsUnsigned Boolean representing the signedness of the type.
   ///
   /// \param BitWidth Size of this int type in bits, or an expression
   /// representing that.
   ///
   /// \param Loc Location of the keyword.
   QualType BuildBitIntType(bool IsUnsigned, Expr *BitWidth, SourceLocation Loc);
 
   /// GetTypeForDeclarator - Convert the type for the specified
   /// declarator to Type instances.
   ///
   /// The result of this call will never be null, but the associated
   /// type may be a null type if there's an unrecoverable error.
   TypeSourceInfo *GetTypeForDeclarator(Declarator &D);
   TypeSourceInfo *GetTypeForDeclaratorCast(Declarator &D, QualType FromTy);
 
   /// Package the given type and TSI into a ParsedType.
   ParsedType CreateParsedType(QualType T, TypeSourceInfo *TInfo);
   static QualType GetTypeFromParser(ParsedType Ty,
                                     TypeSourceInfo **TInfo = nullptr);
 
   TypeResult ActOnTypeName(Declarator &D);
 
   // Check whether the size of array element of type \p EltTy is a multiple of
   // its alignment and return false if it isn't.
   bool checkArrayElementAlignment(QualType EltTy, SourceLocation Loc);
 
   void
   diagnoseIgnoredQualifiers(unsigned DiagID, unsigned Quals,
                             SourceLocation FallbackLoc,
                             SourceLocation ConstQualLoc = SourceLocation(),
                             SourceLocation VolatileQualLoc = SourceLocation(),
                             SourceLocation RestrictQualLoc = SourceLocation(),
                             SourceLocation AtomicQualLoc = SourceLocation(),
                             SourceLocation UnalignedQualLoc = SourceLocation());
 
   /// Retrieve the keyword associated
   IdentifierInfo *getNullabilityKeyword(NullabilityKind nullability);
 
   /// Adjust the calling convention of a method to be the ABI default if it
   /// wasn't specified explicitly.  This handles method types formed from
   /// function type typedefs and typename template arguments.
   void adjustMemberFunctionCC(QualType &T, bool HasThisPointer,
                               bool IsCtorOrDtor, SourceLocation Loc);
 
   // Check if there is an explicit attribute, but only look through parens.
   // The intent is to look for an attribute on the current declarator, but not
   // one that came from a typedef.
   bool hasExplicitCallingConv(QualType T);
 
   /// Check whether a nullability type specifier can be added to the given
   /// type through some means not written in source (e.g. API notes).
   ///
   /// \param Type The type to which the nullability specifier will be
   /// added. On success, this type will be updated appropriately.
   ///
   /// \param Nullability The nullability specifier to add.
   ///
   /// \param DiagLoc The location to use for diagnostics.
   ///
   /// \param AllowArrayTypes Whether to accept nullability specifiers on an
   /// array type (e.g., because it will decay to a pointer).
   ///
   /// \param OverrideExisting Whether to override an existing, locally-specified
   /// nullability specifier rather than complaining about the conflict.
   ///
   /// \returns true if nullability cannot be applied, false otherwise.
   bool CheckImplicitNullabilityTypeSpecifier(QualType &Type,
                                              NullabilityKind Nullability,
                                              SourceLocation DiagLoc,
                                              bool AllowArrayTypes,
                                              bool OverrideExisting);
 
   /// Get the type of expression E, triggering instantiation to complete the
   /// type if necessary -- that is, if the expression refers to a templated
   /// static data member of incomplete array type.
   ///
   /// May still return an incomplete type if instantiation was not possible or
   /// if the type is incomplete for a different reason. Use
   /// RequireCompleteExprType instead if a diagnostic is expected for an
   /// incomplete expression type.
   QualType getCompletedType(Expr *E);
 
   void completeExprArrayBound(Expr *E);
 
   /// Ensure that the type of the given expression is complete.
   ///
   /// This routine checks whether the expression \p E has a complete type. If
   /// the expression refers to an instantiable construct, that instantiation is
   /// performed as needed to complete its type. Furthermore
   /// Sema::RequireCompleteType is called for the expression's type (or in the
   /// case of a reference type, the referred-to type).
   ///
   /// \param E The expression whose type is required to be complete.
   /// \param Kind Selects which completeness rules should be applied.
   /// \param Diagnoser The object that will emit a diagnostic if the type is
   /// incomplete.
   ///
   /// \returns \c true if the type of \p E is incomplete and diagnosed, \c false
   /// otherwise.
   bool RequireCompleteExprType(Expr *E, CompleteTypeKind Kind,
                                TypeDiagnoser &Diagnoser);
   bool RequireCompleteExprType(Expr *E, unsigned DiagID);
 
   template <typename... Ts>
   bool RequireCompleteExprType(Expr *E, unsigned DiagID, const Ts &...Args) {
     BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireCompleteExprType(E, CompleteTypeKind::Default, Diagnoser);
   }
 
   /// Retrieve a version of the type 'T' that is elaborated by Keyword,
   /// qualified by the nested-name-specifier contained in SS, and that is
   /// (re)declared by OwnedTagDecl, which is nullptr if this is not a
   /// (re)declaration.
   QualType getElaboratedType(ElaboratedTypeKeyword Keyword,
                              const CXXScopeSpec &SS, QualType T,
                              TagDecl *OwnedTagDecl = nullptr);
 
   // Returns the underlying type of a decltype with the given expression.
   QualType getDecltypeForExpr(Expr *E);
 
   QualType BuildTypeofExprType(Expr *E, TypeOfKind Kind);
   /// If AsUnevaluated is false, E is treated as though it were an evaluated
   /// context, such as when building a type for decltype(auto).
   QualType BuildDecltypeType(Expr *E, bool AsUnevaluated = true);
 
   QualType ActOnPackIndexingType(QualType Pattern, Expr *IndexExpr,
                                  SourceLocation Loc,
                                  SourceLocation EllipsisLoc);
   QualType BuildPackIndexingType(QualType Pattern, Expr *IndexExpr,
                                  SourceLocation Loc, SourceLocation EllipsisLoc,
                                  bool FullySubstituted = false,
                                  ArrayRef<QualType> Expansions = {});
 
   using UTTKind = UnaryTransformType::UTTKind;
   QualType BuildUnaryTransformType(QualType BaseType, UTTKind UKind,
                                    SourceLocation Loc);
   QualType BuiltinEnumUnderlyingType(QualType BaseType, SourceLocation Loc);
   QualType BuiltinAddPointer(QualType BaseType, SourceLocation Loc);
   QualType BuiltinRemovePointer(QualType BaseType, SourceLocation Loc);
   QualType BuiltinDecay(QualType BaseType, SourceLocation Loc);
   QualType BuiltinAddReference(QualType BaseType, UTTKind UKind,
                                SourceLocation Loc);
   QualType BuiltinRemoveExtent(QualType BaseType, UTTKind UKind,
                                SourceLocation Loc);
   QualType BuiltinRemoveReference(QualType BaseType, UTTKind UKind,
                                   SourceLocation Loc);
   QualType BuiltinChangeCVRQualifiers(QualType BaseType, UTTKind UKind,
                                       SourceLocation Loc);
   QualType BuiltinChangeSignedness(QualType BaseType, UTTKind UKind,
                                    SourceLocation Loc);
 
   /// Ensure that the type T is a literal type.
   ///
   /// This routine checks whether the type @p T is a literal type. If @p T is an
   /// incomplete type, an attempt is made to complete it. If @p T is a literal
   /// type, or @p AllowIncompleteType is true and @p T is an incomplete type,
   /// returns false. Otherwise, this routine issues the diagnostic @p PD (giving
   /// it the type @p T), along with notes explaining why the type is not a
   /// literal type, and returns true.
   ///
   /// @param Loc  The location in the source that the non-literal type
   /// diagnostic should refer to.
   ///
   /// @param T  The type that this routine is examining for literalness.
   ///
   /// @param Diagnoser Emits a diagnostic if T is not a literal type.
   ///
   /// @returns @c true if @p T is not a literal type and a diagnostic was
   /// emitted, @c false otherwise.
   bool RequireLiteralType(SourceLocation Loc, QualType T,
                           TypeDiagnoser &Diagnoser);
   bool RequireLiteralType(SourceLocation Loc, QualType T, unsigned DiagID);
 
   template <typename... Ts>
   bool RequireLiteralType(SourceLocation Loc, QualType T, unsigned DiagID,
                           const Ts &...Args) {
     BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireLiteralType(Loc, T, Diagnoser);
   }
 
   bool isCompleteType(SourceLocation Loc, QualType T,
                       CompleteTypeKind Kind = CompleteTypeKind::Default) {
     return !RequireCompleteTypeImpl(Loc, T, Kind, nullptr);
   }
 
   /// Ensure that the type T is a complete type.
   ///
   /// This routine checks whether the type @p T is complete in any
   /// context where a complete type is required. If @p T is a complete
   /// type, returns false. If @p T is a class template specialization,
   /// this routine then attempts to perform class template
   /// instantiation. If instantiation fails, or if @p T is incomplete
   /// and cannot be completed, issues the diagnostic @p diag (giving it
   /// the type @p T) and returns true.
   ///
   /// @param Loc  The location in the source that the incomplete type
   /// diagnostic should refer to.
   ///
   /// @param T  The type that this routine is examining for completeness.
   ///
   /// @param Kind Selects which completeness rules should be applied.
   ///
   /// @returns @c true if @p T is incomplete and a diagnostic was emitted,
   /// @c false otherwise.
   bool RequireCompleteType(SourceLocation Loc, QualType T,
                            CompleteTypeKind Kind, TypeDiagnoser &Diagnoser);
   bool RequireCompleteType(SourceLocation Loc, QualType T,
                            CompleteTypeKind Kind, unsigned DiagID);
 
   bool RequireCompleteType(SourceLocation Loc, QualType T,
                            TypeDiagnoser &Diagnoser) {
     return RequireCompleteType(Loc, T, CompleteTypeKind::Default, Diagnoser);
   }
   bool RequireCompleteType(SourceLocation Loc, QualType T, unsigned DiagID) {
     return RequireCompleteType(Loc, T, CompleteTypeKind::Default, DiagID);
   }
 
   template <typename... Ts>
   bool RequireCompleteType(SourceLocation Loc, QualType T, unsigned DiagID,
                            const Ts &...Args) {
     BoundTypeDiagnoser<Ts...> Diagnoser(DiagID, Args...);
     return RequireCompleteType(Loc, T, Diagnoser);
   }
 
   /// Determine whether a declaration is visible to name lookup.
   bool isVisible(const NamedDecl *D) {
     return D->isUnconditionallyVisible() ||
            isAcceptableSlow(D, AcceptableKind::Visible);
   }
 
   /// Determine whether a declaration is reachable.
   bool isReachable(const NamedDecl *D) {
     // All visible declarations are reachable.
     return D->isUnconditionallyVisible() ||
            isAcceptableSlow(D, AcceptableKind::Reachable);
   }
 
   /// Determine whether a declaration is acceptable (visible/reachable).
   bool isAcceptable(const NamedDecl *D, AcceptableKind Kind) {
     return Kind == AcceptableKind::Visible ? isVisible(D) : isReachable(D);
   }
 
   /// Determine if \p D and \p Suggested have a structurally compatible
   /// layout as described in C11 6.2.7/1.
   bool hasStructuralCompatLayout(Decl *D, Decl *Suggested);
 
   /// Determine if \p D has a visible definition. If not, suggest a declaration
   /// that should be made visible to expose the definition.
   bool hasVisibleDefinition(NamedDecl *D, NamedDecl **Suggested,
                             bool OnlyNeedComplete = false);
   bool hasVisibleDefinition(const NamedDecl *D) {
     NamedDecl *Hidden;
     return hasVisibleDefinition(const_cast<NamedDecl *>(D), &Hidden);
   }
 
   /// Determine if \p D has a reachable definition. If not, suggest a
   /// declaration that should be made reachable to expose the definition.
   bool hasReachableDefinition(NamedDecl *D, NamedDecl **Suggested,
                               bool OnlyNeedComplete = false);
   bool hasReachableDefinition(NamedDecl *D) {
     NamedDecl *Hidden;
     return hasReachableDefinition(D, &Hidden);
   }
 
   bool hasAcceptableDefinition(NamedDecl *D, NamedDecl **Suggested,
                                AcceptableKind Kind,
                                bool OnlyNeedComplete = false);
   bool hasAcceptableDefinition(NamedDecl *D, AcceptableKind Kind) {
     NamedDecl *Hidden;
     return hasAcceptableDefinition(D, &Hidden, Kind);
   }
 
   /// Try to parse the conditional expression attached to an effect attribute
   /// (e.g. 'nonblocking'). (c.f. Sema::ActOnNoexceptSpec). Return an empty
   /// optional on error.
   std::optional<FunctionEffectMode>
   ActOnEffectExpression(Expr *CondExpr, StringRef AttributeName);
 
 private:
   /// The implementation of RequireCompleteType
   bool RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
                                CompleteTypeKind Kind, TypeDiagnoser *Diagnoser);
 
   /// Nullability type specifiers.
   IdentifierInfo *Ident__Nonnull = nullptr;
   IdentifierInfo *Ident__Nullable = nullptr;
   IdentifierInfo *Ident__Nullable_result = nullptr;
   IdentifierInfo *Ident__Null_unspecified = nullptr;
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name FixIt Helpers
   /// Implementations are in SemaFixItUtils.cpp
   ///@{
 
 public:
   /// Get a string to suggest for zero-initialization of a type.
   std::string getFixItZeroInitializerForType(QualType T,
                                              SourceLocation Loc) const;
   std::string getFixItZeroLiteralForType(QualType T, SourceLocation Loc) const;
 
   ///@}
 
   //
   //
   // -------------------------------------------------------------------------
   //
   //
 
   /// \name Function Effects
   /// Implementations are in SemaFunctionEffects.cpp
   ///@{
 public:
   struct FunctionEffectDiff {
     enum class Kind { Added, Removed, ConditionMismatch };
 
     FunctionEffect::Kind EffectKind;
     Kind DiffKind;
     std::optional<FunctionEffectWithCondition>
         Old; // Invalid when 'Kind' is 'Added'.
     std::optional<FunctionEffectWithCondition>
         New; // Invalid when 'Kind' is 'Removed'.
 
     StringRef effectName() const {
       if (Old)
         return Old.value().Effect.name();
       return New.value().Effect.name();
     }
 
     /// Describes the result of effects differing between a base class's virtual
     /// method and an overriding method in a subclass.
     enum class OverrideResult {
       NoAction,
       Warn,
       Merge // Merge missing effect from base to derived.
     };
 
     /// Return true if adding or removing the effect as part of a type
     /// conversion should generate a diagnostic.
     bool shouldDiagnoseConversion(QualType SrcType,
                                   const FunctionEffectsRef &SrcFX,
                                   QualType DstType,
                                   const FunctionEffectsRef &DstFX) const;
 
     /// Return true if adding or removing the effect in a redeclaration should
     /// generate a diagnostic.
     bool shouldDiagnoseRedeclaration(const FunctionDecl &OldFunction,
                                      const FunctionEffectsRef &OldFX,
                                      const FunctionDecl &NewFunction,
                                      const FunctionEffectsRef &NewFX) const;
 
     /// Return true if adding or removing the effect in a C++ virtual method
     /// override should generate a diagnostic.
     OverrideResult shouldDiagnoseMethodOverride(
         const CXXMethodDecl &OldMethod, const FunctionEffectsRef &OldFX,
         const CXXMethodDecl &NewMethod, const FunctionEffectsRef &NewFX) const;
   };
 
   struct FunctionEffectDiffVector : public SmallVector<FunctionEffectDiff> {
     /// Caller should short-circuit by checking for equality first.
     FunctionEffectDiffVector(const FunctionEffectsRef &Old,
                              const FunctionEffectsRef &New);
   };
 
   /// All functions/lambdas/blocks which have bodies and which have a non-empty
   /// FunctionEffectsRef to be verified.
   SmallVector<const Decl *> DeclsWithEffectsToVerify;
 
   /// The union of all effects present on DeclsWithEffectsToVerify. Conditions
   /// are all null.
   FunctionEffectKindSet AllEffectsToVerify;
 
 public:
   /// Warn and return true if adding a function effect to a set would create a
   /// conflict.
   bool diagnoseConflictingFunctionEffect(const FunctionEffectsRef &FX,
                                          const FunctionEffectWithCondition &EC,
                                          SourceLocation NewAttrLoc);
 
   // Report a failure to merge function effects between declarations due to a
   // conflict.
   void
   diagnoseFunctionEffectMergeConflicts(const FunctionEffectSet::Conflicts &Errs,
                                        SourceLocation NewLoc,
                                        SourceLocation OldLoc);
 
   /// Inline checks from the start of maybeAddDeclWithEffects, to
   /// minimize performance impact on code not using effects.
   template <class FuncOrBlockDecl>
   void maybeAddDeclWithEffects(FuncOrBlockDecl *D) {
     if (Context.hasAnyFunctionEffects())
       if (FunctionEffectsRef FX = D->getFunctionEffects(); !FX.empty())
         maybeAddDeclWithEffects(D, FX);
   }
 
   /// Potentially add a FunctionDecl or BlockDecl to DeclsWithEffectsToVerify.
   void maybeAddDeclWithEffects(const Decl *D, const FunctionEffectsRef &FX);
 
   /// Unconditionally add a Decl to DeclsWithEfffectsToVerify.
   void addDeclWithEffects(const Decl *D, const FunctionEffectsRef &FX);
 
   void performFunctionEffectAnalysis(TranslationUnitDecl *TU);
 
   ///@}
 };
 
 DeductionFailureInfo
 MakeDeductionFailureInfo(ASTContext &Context, TemplateDeductionResult TDK,
                          sema::TemplateDeductionInfo &Info);
 
 /// Contains a late templated function.
 /// Will be parsed at the end of the translation unit, used by Sema & Parser.
 struct LateParsedTemplate {
   CachedTokens Toks;
   /// The template function declaration to be late parsed.
   Decl *D;
   /// Floating-point options in the point of definition.
   FPOptions FPO;
 };
 
 template <>
 void Sema::PragmaStack<Sema::AlignPackInfo>::Act(SourceLocation PragmaLocation,
                                                  PragmaMsStackAction Action,
                                                  llvm::StringRef StackSlotLabel,
                                                  AlignPackInfo Value);
 } // end namespace clang
 
 #endif