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 //===- DeclCXX.h - Classes for representing C++ declarations --*- 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
 //
 //===----------------------------------------------------------------------===//
 //
 /// \file
 /// Defines the C++ Decl subclasses, other than those for templates
 /// (found in DeclTemplate.h) and friends (in DeclFriend.h).
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_AST_DECLCXX_H
 #define LLVM_CLANG_AST_DECLCXX_H
 
 #include "clang/AST/ASTUnresolvedSet.h"
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclarationName.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExternalASTSource.h"
 #include "clang/AST/LambdaCapture.h"
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/AST/Redeclarable.h"
 #include "clang/AST/Stmt.h"
 #include "clang/AST/Type.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/AST/UnresolvedSet.h"
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/Lambda.h"
 #include "clang/Basic/LangOptions.h"
 #include "clang/Basic/OperatorKinds.h"
 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/Specifiers.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/TinyPtrVector.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/PointerLikeTypeTraits.h"
 #include "llvm/Support/TrailingObjects.h"
 #include <cassert>
 #include <cstddef>
 #include <iterator>
 #include <memory>
 #include <vector>
 
 namespace clang {
 
 class ASTContext;
 class ClassTemplateDecl;
 class ConstructorUsingShadowDecl;
 class CXXBasePath;
 class CXXBasePaths;
 class CXXConstructorDecl;
 class CXXDestructorDecl;
 class CXXFinalOverriderMap;
 class CXXIndirectPrimaryBaseSet;
 class CXXMethodDecl;
 class DecompositionDecl;
 class FriendDecl;
 class FunctionTemplateDecl;
 class IdentifierInfo;
 class MemberSpecializationInfo;
 class BaseUsingDecl;
 class TemplateDecl;
 class TemplateParameterList;
 class UsingDecl;
 
 /// Represents an access specifier followed by colon ':'.
 ///
 /// An objects of this class represents sugar for the syntactic occurrence
 /// of an access specifier followed by a colon in the list of member
 /// specifiers of a C++ class definition.
 ///
 /// Note that they do not represent other uses of access specifiers,
 /// such as those occurring in a list of base specifiers.
 /// Also note that this class has nothing to do with so-called
 /// "access declarations" (C++98 11.3 [class.access.dcl]).
 class AccessSpecDecl : public Decl {
   /// The location of the ':'.
   SourceLocation ColonLoc;
 
   AccessSpecDecl(AccessSpecifier AS, DeclContext *DC,
                  SourceLocation ASLoc, SourceLocation ColonLoc)
     : Decl(AccessSpec, DC, ASLoc), ColonLoc(ColonLoc) {
     setAccess(AS);
   }
 
   AccessSpecDecl(EmptyShell Empty) : Decl(AccessSpec, Empty) {}
 
   virtual void anchor();
 
 public:
   /// The location of the access specifier.
   SourceLocation getAccessSpecifierLoc() const { return getLocation(); }
 
   /// Sets the location of the access specifier.
   void setAccessSpecifierLoc(SourceLocation ASLoc) { setLocation(ASLoc); }
 
   /// The location of the colon following the access specifier.
   SourceLocation getColonLoc() const { return ColonLoc; }
 
   /// Sets the location of the colon.
   void setColonLoc(SourceLocation CLoc) { ColonLoc = CLoc; }
 
   SourceRange getSourceRange() const override LLVM_READONLY {
     return SourceRange(getAccessSpecifierLoc(), getColonLoc());
   }
 
   static AccessSpecDecl *Create(ASTContext &C, AccessSpecifier AS,
                                 DeclContext *DC, SourceLocation ASLoc,
                                 SourceLocation ColonLoc) {
     return new (C, DC) AccessSpecDecl(AS, DC, ASLoc, ColonLoc);
   }
 
   static AccessSpecDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == AccessSpec; }
 };
 
 /// Represents a base class of a C++ class.
 ///
 /// Each CXXBaseSpecifier represents a single, direct base class (or
 /// struct) of a C++ class (or struct). It specifies the type of that
 /// base class, whether it is a virtual or non-virtual base, and what
 /// level of access (public, protected, private) is used for the
 /// derivation. For example:
 ///
 /// \code
 ///   class A { };
 ///   class B { };
 ///   class C : public virtual A, protected B { };
 /// \endcode
 ///
 /// In this code, C will have two CXXBaseSpecifiers, one for "public
 /// virtual A" and the other for "protected B".
 class CXXBaseSpecifier {
   /// The source code range that covers the full base
   /// specifier, including the "virtual" (if present) and access
   /// specifier (if present).
   SourceRange Range;
 
   /// The source location of the ellipsis, if this is a pack
   /// expansion.
   SourceLocation EllipsisLoc;
 
   /// Whether this is a virtual base class or not.
   LLVM_PREFERRED_TYPE(bool)
   unsigned Virtual : 1;
 
   /// Whether this is the base of a class (true) or of a struct (false).
   ///
   /// This determines the mapping from the access specifier as written in the
   /// source code to the access specifier used for semantic analysis.
   LLVM_PREFERRED_TYPE(bool)
   unsigned BaseOfClass : 1;
 
   /// Access specifier as written in the source code (may be AS_none).
   ///
   /// The actual type of data stored here is an AccessSpecifier, but we use
   /// "unsigned" here to work around Microsoft ABI.
   LLVM_PREFERRED_TYPE(AccessSpecifier)
   unsigned Access : 2;
 
   /// Whether the class contains a using declaration
   /// to inherit the named class's constructors.
   LLVM_PREFERRED_TYPE(bool)
   unsigned InheritConstructors : 1;
 
   /// The type of the base class.
   ///
   /// This will be a class or struct (or a typedef of such). The source code
   /// range does not include the \c virtual or the access specifier.
   TypeSourceInfo *BaseTypeInfo;
 
 public:
   CXXBaseSpecifier() = default;
   CXXBaseSpecifier(SourceRange R, bool V, bool BC, AccessSpecifier A,
                    TypeSourceInfo *TInfo, SourceLocation EllipsisLoc)
     : Range(R), EllipsisLoc(EllipsisLoc), Virtual(V), BaseOfClass(BC),
       Access(A), InheritConstructors(false), BaseTypeInfo(TInfo) {}
 
   /// Retrieves the source range that contains the entire base specifier.
   SourceRange getSourceRange() const LLVM_READONLY { return Range; }
   SourceLocation getBeginLoc() const LLVM_READONLY { return Range.getBegin(); }
   SourceLocation getEndLoc() const LLVM_READONLY { return Range.getEnd(); }
 
   /// Get the location at which the base class type was written.
   SourceLocation getBaseTypeLoc() const LLVM_READONLY {
     return BaseTypeInfo->getTypeLoc().getBeginLoc();
   }
 
   /// Determines whether the base class is a virtual base class (or not).
   bool isVirtual() const { return Virtual; }
 
   /// Determine whether this base class is a base of a class declared
   /// with the 'class' keyword (vs. one declared with the 'struct' keyword).
   bool isBaseOfClass() const { return BaseOfClass; }
 
   /// Determine whether this base specifier is a pack expansion.
   bool isPackExpansion() const { return EllipsisLoc.isValid(); }
 
   /// Determine whether this base class's constructors get inherited.
   bool getInheritConstructors() const { return InheritConstructors; }
 
   /// Set that this base class's constructors should be inherited.
   void setInheritConstructors(bool Inherit = true) {
     InheritConstructors = Inherit;
   }
 
   /// For a pack expansion, determine the location of the ellipsis.
   SourceLocation getEllipsisLoc() const {
     return EllipsisLoc;
   }
 
   /// Returns the access specifier for this base specifier.
   ///
   /// This is the actual base specifier as used for semantic analysis, so
   /// the result can never be AS_none. To retrieve the access specifier as
   /// written in the source code, use getAccessSpecifierAsWritten().
   AccessSpecifier getAccessSpecifier() const {
     if ((AccessSpecifier)Access == AS_none)
       return BaseOfClass? AS_private : AS_public;
     else
       return (AccessSpecifier)Access;
   }
 
   /// Retrieves the access specifier as written in the source code
   /// (which may mean that no access specifier was explicitly written).
   ///
   /// Use getAccessSpecifier() to retrieve the access specifier for use in
   /// semantic analysis.
   AccessSpecifier getAccessSpecifierAsWritten() const {
     return (AccessSpecifier)Access;
   }
 
   /// Retrieves the type of the base class.
   ///
   /// This type will always be an unqualified class type.
   QualType getType() const {
     return BaseTypeInfo->getType().getUnqualifiedType();
   }
 
   /// Retrieves the type and source location of the base class.
   TypeSourceInfo *getTypeSourceInfo() const { return BaseTypeInfo; }
 };
 
 /// Represents a C++ struct/union/class.
 class CXXRecordDecl : public RecordDecl {
   friend class ASTDeclMerger;
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
   friend class ASTNodeImporter;
   friend class ASTReader;
   friend class ASTRecordWriter;
   friend class ASTWriter;
   friend class DeclContext;
   friend class LambdaExpr;
   friend class ODRDiagsEmitter;
 
   friend void FunctionDecl::setIsPureVirtual(bool);
   friend void TagDecl::startDefinition();
 
   /// Values used in DefinitionData fields to represent special members.
   enum SpecialMemberFlags {
     SMF_DefaultConstructor = 0x1,
     SMF_CopyConstructor = 0x2,
     SMF_MoveConstructor = 0x4,
     SMF_CopyAssignment = 0x8,
     SMF_MoveAssignment = 0x10,
     SMF_Destructor = 0x20,
     SMF_All = 0x3f
   };
 
 public:
   enum LambdaDependencyKind {
     LDK_Unknown = 0,
     LDK_AlwaysDependent,
     LDK_NeverDependent,
   };
 
 private:
   struct DefinitionData {
     #define FIELD(Name, Width, Merge) \
     unsigned Name : Width;
     #include "CXXRecordDeclDefinitionBits.def"
 
     /// Whether this class describes a C++ lambda.
     LLVM_PREFERRED_TYPE(bool)
     unsigned IsLambda : 1;
 
     /// Whether we are currently parsing base specifiers.
     LLVM_PREFERRED_TYPE(bool)
     unsigned IsParsingBaseSpecifiers : 1;
 
     /// True when visible conversion functions are already computed
     /// and are available.
     LLVM_PREFERRED_TYPE(bool)
     unsigned ComputedVisibleConversions : 1;
 
     LLVM_PREFERRED_TYPE(bool)
     unsigned HasODRHash : 1;
 
     /// A hash of parts of the class to help in ODR checking.
     unsigned ODRHash = 0;
 
     /// The number of base class specifiers in Bases.
     unsigned NumBases = 0;
 
     /// The number of virtual base class specifiers in VBases.
     unsigned NumVBases = 0;
 
     /// Base classes of this class.
     ///
     /// FIXME: This is wasted space for a union.
     LazyCXXBaseSpecifiersPtr Bases;
 
     /// direct and indirect virtual base classes of this class.
     LazyCXXBaseSpecifiersPtr VBases;
 
     /// The conversion functions of this C++ class (but not its
     /// inherited conversion functions).
     ///
     /// Each of the entries in this overload set is a CXXConversionDecl.
     LazyASTUnresolvedSet Conversions;
 
     /// The conversion functions of this C++ class and all those
     /// inherited conversion functions that are visible in this class.
     ///
     /// Each of the entries in this overload set is a CXXConversionDecl or a
     /// FunctionTemplateDecl.
     LazyASTUnresolvedSet VisibleConversions;
 
     /// The declaration which defines this record.
     CXXRecordDecl *Definition;
 
     /// The first friend declaration in this class, or null if there
     /// aren't any.
     ///
     /// This is actually currently stored in reverse order.
     LazyDeclPtr FirstFriend;
 
     DefinitionData(CXXRecordDecl *D);
 
     /// Retrieve the set of direct base classes.
     CXXBaseSpecifier *getBases() const {
       if (!Bases.isOffset())
         return Bases.get(nullptr);
       return getBasesSlowCase();
     }
 
     /// Retrieve the set of virtual base classes.
     CXXBaseSpecifier *getVBases() const {
       if (!VBases.isOffset())
         return VBases.get(nullptr);
       return getVBasesSlowCase();
     }
 
     ArrayRef<CXXBaseSpecifier> bases() const {
       return llvm::ArrayRef(getBases(), NumBases);
     }
 
     ArrayRef<CXXBaseSpecifier> vbases() const {
       return llvm::ArrayRef(getVBases(), NumVBases);
     }
 
   private:
     CXXBaseSpecifier *getBasesSlowCase() const;
     CXXBaseSpecifier *getVBasesSlowCase() const;
   };
 
   struct DefinitionData *DefinitionData;
 
   /// Describes a C++ closure type (generated by a lambda expression).
   struct LambdaDefinitionData : public DefinitionData {
     using Capture = LambdaCapture;
 
     /// Whether this lambda is known to be dependent, even if its
     /// context isn't dependent.
     ///
     /// A lambda with a non-dependent context can be dependent if it occurs
     /// within the default argument of a function template, because the
     /// lambda will have been created with the enclosing context as its
     /// declaration context, rather than function. This is an unfortunate
     /// artifact of having to parse the default arguments before.
     LLVM_PREFERRED_TYPE(LambdaDependencyKind)
     unsigned DependencyKind : 2;
 
     /// Whether this lambda is a generic lambda.
     LLVM_PREFERRED_TYPE(bool)
     unsigned IsGenericLambda : 1;
 
     /// The Default Capture.
     LLVM_PREFERRED_TYPE(LambdaCaptureDefault)
     unsigned CaptureDefault : 2;
 
     /// The number of captures in this lambda is limited 2^NumCaptures.
     unsigned NumCaptures : 15;
 
     /// The number of explicit captures in this lambda.
     unsigned NumExplicitCaptures : 12;
 
     /// Has known `internal` linkage.
     LLVM_PREFERRED_TYPE(bool)
     unsigned HasKnownInternalLinkage : 1;
 
     /// The number used to indicate this lambda expression for name
     /// mangling in the Itanium C++ ABI.
     unsigned ManglingNumber : 31;
 
     /// The index of this lambda within its context declaration. This is not in
     /// general the same as the mangling number.
     unsigned IndexInContext;
 
     /// The declaration that provides context for this lambda, if the
     /// actual DeclContext does not suffice. This is used for lambdas that
     /// occur within default arguments of function parameters within the class
     /// or within a data member initializer.
     LazyDeclPtr ContextDecl;
 
     /// The lists of captures, both explicit and implicit, for this
     /// lambda. One list is provided for each merged copy of the lambda.
     /// The first list corresponds to the canonical definition.
     /// The destructor is registered by AddCaptureList when necessary.
     llvm::TinyPtrVector<Capture*> Captures;
 
     /// The type of the call method.
     TypeSourceInfo *MethodTyInfo;
 
     LambdaDefinitionData(CXXRecordDecl *D, TypeSourceInfo *Info, unsigned DK,
                          bool IsGeneric, LambdaCaptureDefault CaptureDefault)
         : DefinitionData(D), DependencyKind(DK), IsGenericLambda(IsGeneric),
           CaptureDefault(CaptureDefault), NumCaptures(0),
           NumExplicitCaptures(0), HasKnownInternalLinkage(0), ManglingNumber(0),
           IndexInContext(0), MethodTyInfo(Info) {
       IsLambda = true;
 
       // C++1z [expr.prim.lambda]p4:
       //   This class type is not an aggregate type.
       Aggregate = false;
       PlainOldData = false;
     }
 
     // Add a list of captures.
     void AddCaptureList(ASTContext &Ctx, Capture *CaptureList);
   };
 
   struct DefinitionData *dataPtr() const {
     // Complete the redecl chain (if necessary).
     getMostRecentDecl();
     return DefinitionData;
   }
 
   struct DefinitionData &data() const {
     auto *DD = dataPtr();
     assert(DD && "queried property of class with no definition");
     return *DD;
   }
 
   struct LambdaDefinitionData &getLambdaData() const {
     // No update required: a merged definition cannot change any lambda
     // properties.
     auto *DD = DefinitionData;
     assert(DD && DD->IsLambda && "queried lambda property of non-lambda class");
     return static_cast<LambdaDefinitionData&>(*DD);
   }
 
   /// The template or declaration that this declaration
   /// describes or was instantiated from, respectively.
   ///
   /// For non-templates, this value will be null. For record
   /// declarations that describe a class template, this will be a
   /// pointer to a ClassTemplateDecl. For member
   /// classes of class template specializations, this will be the
   /// MemberSpecializationInfo referring to the member class that was
   /// instantiated or specialized.
   llvm::PointerUnion<ClassTemplateDecl *, MemberSpecializationInfo *>
       TemplateOrInstantiation;
 
   /// Called from setBases and addedMember to notify the class that a
   /// direct or virtual base class or a member of class type has been added.
   void addedClassSubobject(CXXRecordDecl *Base);
 
   /// Notify the class that member has been added.
   ///
   /// This routine helps maintain information about the class based on which
   /// members have been added. It will be invoked by DeclContext::addDecl()
   /// whenever a member is added to this record.
   void addedMember(Decl *D);
 
   void markedVirtualFunctionPure();
 
   /// Get the head of our list of friend declarations, possibly
   /// deserializing the friends from an external AST source.
   FriendDecl *getFirstFriend() const;
 
   /// Determine whether this class has an empty base class subobject of type X
   /// or of one of the types that might be at offset 0 within X (per the C++
   /// "standard layout" rules).
   bool hasSubobjectAtOffsetZeroOfEmptyBaseType(ASTContext &Ctx,
                                                const CXXRecordDecl *X);
 
 protected:
   CXXRecordDecl(Kind K, TagKind TK, const ASTContext &C, DeclContext *DC,
                 SourceLocation StartLoc, SourceLocation IdLoc,
                 IdentifierInfo *Id, CXXRecordDecl *PrevDecl);
 
 public:
   /// Iterator that traverses the base classes of a class.
   using base_class_iterator = CXXBaseSpecifier *;
 
   /// Iterator that traverses the base classes of a class.
   using base_class_const_iterator = const CXXBaseSpecifier *;
 
   CXXRecordDecl *getCanonicalDecl() override {
     return cast<CXXRecordDecl>(RecordDecl::getCanonicalDecl());
   }
 
   const CXXRecordDecl *getCanonicalDecl() const {
     return const_cast<CXXRecordDecl*>(this)->getCanonicalDecl();
   }
 
   CXXRecordDecl *getPreviousDecl() {
     return cast_or_null<CXXRecordDecl>(
             static_cast<RecordDecl *>(this)->getPreviousDecl());
   }
 
   const CXXRecordDecl *getPreviousDecl() const {
     return const_cast<CXXRecordDecl*>(this)->getPreviousDecl();
   }
 
   CXXRecordDecl *getMostRecentDecl() {
     return cast<CXXRecordDecl>(
             static_cast<RecordDecl *>(this)->getMostRecentDecl());
   }
 
   const CXXRecordDecl *getMostRecentDecl() const {
     return const_cast<CXXRecordDecl*>(this)->getMostRecentDecl();
   }
 
   CXXRecordDecl *getMostRecentNonInjectedDecl() {
     CXXRecordDecl *Recent =
         static_cast<CXXRecordDecl *>(this)->getMostRecentDecl();
     while (Recent->isInjectedClassName()) {
       // FIXME: Does injected class name need to be in the redeclarations chain?
       assert(Recent->getPreviousDecl());
       Recent = Recent->getPreviousDecl();
     }
     return Recent;
   }
 
   const CXXRecordDecl *getMostRecentNonInjectedDecl() const {
     return const_cast<CXXRecordDecl*>(this)->getMostRecentNonInjectedDecl();
   }
 
   CXXRecordDecl *getDefinition() const {
     // We only need an update if we don't already know which
     // declaration is the definition.
     auto *DD = DefinitionData ? DefinitionData : dataPtr();
     return DD ? DD->Definition : nullptr;
   }
 
   bool hasDefinition() const { return DefinitionData || dataPtr(); }
 
   static CXXRecordDecl *Create(const ASTContext &C, TagKind TK, DeclContext *DC,
                                SourceLocation StartLoc, SourceLocation IdLoc,
                                IdentifierInfo *Id,
                                CXXRecordDecl *PrevDecl = nullptr,
                                bool DelayTypeCreation = false);
   static CXXRecordDecl *CreateLambda(const ASTContext &C, DeclContext *DC,
                                      TypeSourceInfo *Info, SourceLocation Loc,
                                      unsigned DependencyKind, bool IsGeneric,
                                      LambdaCaptureDefault CaptureDefault);
   static CXXRecordDecl *CreateDeserialized(const ASTContext &C,
                                            GlobalDeclID ID);
 
   bool isDynamicClass() const {
     return data().Polymorphic || data().NumVBases != 0;
   }
 
   /// @returns true if class is dynamic or might be dynamic because the
   /// definition is incomplete of dependent.
   bool mayBeDynamicClass() const {
     return !hasDefinition() || isDynamicClass() || hasAnyDependentBases();
   }
 
   /// @returns true if class is non dynamic or might be non dynamic because the
   /// definition is incomplete of dependent.
   bool mayBeNonDynamicClass() const {
     return !hasDefinition() || !isDynamicClass() || hasAnyDependentBases();
   }
 
   void setIsParsingBaseSpecifiers() { data().IsParsingBaseSpecifiers = true; }
 
   bool isParsingBaseSpecifiers() const {
     return data().IsParsingBaseSpecifiers;
   }
 
   unsigned getODRHash() const;
 
   /// Sets the base classes of this struct or class.
   void setBases(CXXBaseSpecifier const * const *Bases, unsigned NumBases);
 
   /// Retrieves the number of base classes of this class.
   unsigned getNumBases() const { return data().NumBases; }
 
   using base_class_range = llvm::iterator_range<base_class_iterator>;
   using base_class_const_range =
       llvm::iterator_range<base_class_const_iterator>;
 
   base_class_range bases() {
     return base_class_range(bases_begin(), bases_end());
   }
   base_class_const_range bases() const {
     return base_class_const_range(bases_begin(), bases_end());
   }
 
   base_class_iterator bases_begin() { return data().getBases(); }
   base_class_const_iterator bases_begin() const { return data().getBases(); }
   base_class_iterator bases_end() { return bases_begin() + data().NumBases; }
   base_class_const_iterator bases_end() const {
     return bases_begin() + data().NumBases;
   }
 
   /// Retrieves the number of virtual base classes of this class.
   unsigned getNumVBases() const { return data().NumVBases; }
 
   base_class_range vbases() {
     return base_class_range(vbases_begin(), vbases_end());
   }
   base_class_const_range vbases() const {
     return base_class_const_range(vbases_begin(), vbases_end());
   }
 
   base_class_iterator vbases_begin() { return data().getVBases(); }
   base_class_const_iterator vbases_begin() const { return data().getVBases(); }
   base_class_iterator vbases_end() { return vbases_begin() + data().NumVBases; }
   base_class_const_iterator vbases_end() const {
     return vbases_begin() + data().NumVBases;
   }
 
   /// Determine whether this class has any dependent base classes which
   /// are not the current instantiation.
   bool hasAnyDependentBases() const;
 
   /// Iterator access to method members.  The method iterator visits
   /// all method members of the class, including non-instance methods,
   /// special methods, etc.
   using method_iterator = specific_decl_iterator<CXXMethodDecl>;
   using method_range =
       llvm::iterator_range<specific_decl_iterator<CXXMethodDecl>>;
 
   method_range methods() const {
     return method_range(method_begin(), method_end());
   }
 
   /// Method begin iterator.  Iterates in the order the methods
   /// were declared.
   method_iterator method_begin() const {
     return method_iterator(decls_begin());
   }
 
   /// Method past-the-end iterator.
   method_iterator method_end() const {
     return method_iterator(decls_end());
   }
 
   /// Iterator access to constructor members.
   using ctor_iterator = specific_decl_iterator<CXXConstructorDecl>;
   using ctor_range =
       llvm::iterator_range<specific_decl_iterator<CXXConstructorDecl>>;
 
   ctor_range ctors() const { return ctor_range(ctor_begin(), ctor_end()); }
 
   ctor_iterator ctor_begin() const {
     return ctor_iterator(decls_begin());
   }
 
   ctor_iterator ctor_end() const {
     return ctor_iterator(decls_end());
   }
 
   /// An iterator over friend declarations.  All of these are defined
   /// in DeclFriend.h.
   class friend_iterator;
   using friend_range = llvm::iterator_range<friend_iterator>;
 
   friend_range friends() const;
   friend_iterator friend_begin() const;
   friend_iterator friend_end() const;
   void pushFriendDecl(FriendDecl *FD);
 
   /// Determines whether this record has any friends.
   bool hasFriends() const {
     return data().FirstFriend.isValid();
   }
 
   /// \c true if a defaulted copy constructor for this class would be
   /// deleted.
   bool defaultedCopyConstructorIsDeleted() const {
     assert((!needsOverloadResolutionForCopyConstructor() ||
             (data().DeclaredSpecialMembers & SMF_CopyConstructor)) &&
            "this property has not yet been computed by Sema");
     return data().DefaultedCopyConstructorIsDeleted;
   }
 
   /// \c true if a defaulted move constructor for this class would be
   /// deleted.
   bool defaultedMoveConstructorIsDeleted() const {
     assert((!needsOverloadResolutionForMoveConstructor() ||
             (data().DeclaredSpecialMembers & SMF_MoveConstructor)) &&
            "this property has not yet been computed by Sema");
     return data().DefaultedMoveConstructorIsDeleted;
   }
 
   /// \c true if a defaulted destructor for this class would be deleted.
   bool defaultedDestructorIsDeleted() const {
     assert((!needsOverloadResolutionForDestructor() ||
             (data().DeclaredSpecialMembers & SMF_Destructor)) &&
            "this property has not yet been computed by Sema");
     return data().DefaultedDestructorIsDeleted;
   }
 
   /// \c true if we know for sure that this class has a single,
   /// accessible, unambiguous copy constructor that is not deleted.
   bool hasSimpleCopyConstructor() const {
     return !hasUserDeclaredCopyConstructor() &&
            !data().DefaultedCopyConstructorIsDeleted;
   }
 
   /// \c true if we know for sure that this class has a single,
   /// accessible, unambiguous move constructor that is not deleted.
   bool hasSimpleMoveConstructor() const {
     return !hasUserDeclaredMoveConstructor() && hasMoveConstructor() &&
            !data().DefaultedMoveConstructorIsDeleted;
   }
 
   /// \c true if we know for sure that this class has a single,
   /// accessible, unambiguous copy assignment operator that is not deleted.
   bool hasSimpleCopyAssignment() const {
     return !hasUserDeclaredCopyAssignment() &&
            !data().DefaultedCopyAssignmentIsDeleted;
   }
 
   /// \c true if we know for sure that this class has a single,
   /// accessible, unambiguous move assignment operator that is not deleted.
   bool hasSimpleMoveAssignment() const {
     return !hasUserDeclaredMoveAssignment() && hasMoveAssignment() &&
            !data().DefaultedMoveAssignmentIsDeleted;
   }
 
   /// \c true if we know for sure that this class has an accessible
   /// destructor that is not deleted.
   bool hasSimpleDestructor() const {
     return !hasUserDeclaredDestructor() &&
            !data().DefaultedDestructorIsDeleted;
   }
 
   /// Determine whether this class has any default constructors.
   bool hasDefaultConstructor() const {
     return (data().DeclaredSpecialMembers & SMF_DefaultConstructor) ||
            needsImplicitDefaultConstructor();
   }
 
   /// Determine if we need to declare a default constructor for
   /// this class.
   ///
   /// This value is used for lazy creation of default constructors.
   bool needsImplicitDefaultConstructor() const {
     return (!data().UserDeclaredConstructor &&
             !(data().DeclaredSpecialMembers & SMF_DefaultConstructor) &&
             (!isLambda() || lambdaIsDefaultConstructibleAndAssignable())) ||
            // FIXME: Proposed fix to core wording issue: if a class inherits
            // a default constructor and doesn't explicitly declare one, one
            // is declared implicitly.
            (data().HasInheritedDefaultConstructor &&
             !(data().DeclaredSpecialMembers & SMF_DefaultConstructor));
   }
 
   /// Determine whether this class has any user-declared constructors.
   ///
   /// When true, a default constructor will not be implicitly declared.
   bool hasUserDeclaredConstructor() const {
     return data().UserDeclaredConstructor;
   }
 
   /// Whether this class has a user-provided default constructor
   /// per C++11.
   bool hasUserProvidedDefaultConstructor() const {
     return data().UserProvidedDefaultConstructor;
   }
 
   /// Determine whether this class has a user-declared copy constructor.
   ///
   /// When false, a copy constructor will be implicitly declared.
   bool hasUserDeclaredCopyConstructor() const {
     return data().UserDeclaredSpecialMembers & SMF_CopyConstructor;
   }
 
   /// Determine whether this class needs an implicit copy
   /// constructor to be lazily declared.
   bool needsImplicitCopyConstructor() const {
     return !(data().DeclaredSpecialMembers & SMF_CopyConstructor);
   }
 
   /// Determine whether we need to eagerly declare a defaulted copy
   /// constructor for this class.
   bool needsOverloadResolutionForCopyConstructor() const {
     // C++17 [class.copy.ctor]p6:
     //   If the class definition declares a move constructor or move assignment
     //   operator, the implicitly declared copy constructor is defined as
     //   deleted.
     // In MSVC mode, sometimes a declared move assignment does not delete an
     // implicit copy constructor, so defer this choice to Sema.
     if (data().UserDeclaredSpecialMembers &
         (SMF_MoveConstructor | SMF_MoveAssignment))
       return true;
     return data().NeedOverloadResolutionForCopyConstructor;
   }
 
   /// Determine whether an implicit copy constructor for this type
   /// would have a parameter with a const-qualified reference type.
   bool implicitCopyConstructorHasConstParam() const {
     return data().ImplicitCopyConstructorCanHaveConstParamForNonVBase &&
            (isAbstract() ||
             data().ImplicitCopyConstructorCanHaveConstParamForVBase);
   }
 
   /// Determine whether this class has a copy constructor with
   /// a parameter type which is a reference to a const-qualified type.
   bool hasCopyConstructorWithConstParam() const {
     return data().HasDeclaredCopyConstructorWithConstParam ||
            (needsImplicitCopyConstructor() &&
             implicitCopyConstructorHasConstParam());
   }
 
   /// Whether this class has a user-declared move constructor or
   /// assignment operator.
   ///
   /// When false, a move constructor and assignment operator may be
   /// implicitly declared.
   bool hasUserDeclaredMoveOperation() const {
     return data().UserDeclaredSpecialMembers &
              (SMF_MoveConstructor | SMF_MoveAssignment);
   }
 
   /// Determine whether this class has had a move constructor
   /// declared by the user.
   bool hasUserDeclaredMoveConstructor() const {
     return data().UserDeclaredSpecialMembers & SMF_MoveConstructor;
   }
 
   /// Determine whether this class has a move constructor.
   bool hasMoveConstructor() const {
     return (data().DeclaredSpecialMembers & SMF_MoveConstructor) ||
            needsImplicitMoveConstructor();
   }
 
   /// Set that we attempted to declare an implicit copy
   /// constructor, but overload resolution failed so we deleted it.
   void setImplicitCopyConstructorIsDeleted() {
     assert((data().DefaultedCopyConstructorIsDeleted ||
             needsOverloadResolutionForCopyConstructor()) &&
            "Copy constructor should not be deleted");
     data().DefaultedCopyConstructorIsDeleted = true;
   }
 
   /// Set that we attempted to declare an implicit move
   /// constructor, but overload resolution failed so we deleted it.
   void setImplicitMoveConstructorIsDeleted() {
     assert((data().DefaultedMoveConstructorIsDeleted ||
             needsOverloadResolutionForMoveConstructor()) &&
            "move constructor should not be deleted");
     data().DefaultedMoveConstructorIsDeleted = true;
   }
 
   /// Set that we attempted to declare an implicit destructor,
   /// but overload resolution failed so we deleted it.
   void setImplicitDestructorIsDeleted() {
     assert((data().DefaultedDestructorIsDeleted ||
             needsOverloadResolutionForDestructor()) &&
            "destructor should not be deleted");
     data().DefaultedDestructorIsDeleted = true;
     // C++23 [dcl.constexpr]p3.2:
     //   if the function is a constructor or destructor, its class does not have
     //   any virtual base classes.
     // C++20 [dcl.constexpr]p5:
     //   The definition of a constexpr destructor whose function-body is
     //   not = delete shall additionally satisfy...
     data().DefaultedDestructorIsConstexpr = data().NumVBases == 0;
   }
 
   /// Determine whether this class should get an implicit move
   /// constructor or if any existing special member function inhibits this.
   bool needsImplicitMoveConstructor() const {
     return !(data().DeclaredSpecialMembers & SMF_MoveConstructor) &&
            !hasUserDeclaredCopyConstructor() &&
            !hasUserDeclaredCopyAssignment() &&
            !hasUserDeclaredMoveAssignment() &&
            !hasUserDeclaredDestructor();
   }
 
   /// Determine whether we need to eagerly declare a defaulted move
   /// constructor for this class.
   bool needsOverloadResolutionForMoveConstructor() const {
     return data().NeedOverloadResolutionForMoveConstructor;
   }
 
   /// Determine whether this class has a user-declared copy assignment
   /// operator.
   ///
   /// When false, a copy assignment operator will be implicitly declared.
   bool hasUserDeclaredCopyAssignment() const {
     return data().UserDeclaredSpecialMembers & SMF_CopyAssignment;
   }
 
   /// Set that we attempted to declare an implicit copy assignment
   /// operator, but overload resolution failed so we deleted it.
   void setImplicitCopyAssignmentIsDeleted() {
     assert((data().DefaultedCopyAssignmentIsDeleted ||
             needsOverloadResolutionForCopyAssignment()) &&
            "copy assignment should not be deleted");
     data().DefaultedCopyAssignmentIsDeleted = true;
   }
 
   /// Determine whether this class needs an implicit copy
   /// assignment operator to be lazily declared.
   bool needsImplicitCopyAssignment() const {
     return !(data().DeclaredSpecialMembers & SMF_CopyAssignment);
   }
 
   /// Determine whether we need to eagerly declare a defaulted copy
   /// assignment operator for this class.
   bool needsOverloadResolutionForCopyAssignment() const {
     // C++20 [class.copy.assign]p2:
     //   If the class definition declares a move constructor or move assignment
     //   operator, the implicitly declared copy assignment operator is defined
     //   as deleted.
     // In MSVC mode, sometimes a declared move constructor does not delete an
     // implicit copy assignment, so defer this choice to Sema.
     if (data().UserDeclaredSpecialMembers &
         (SMF_MoveConstructor | SMF_MoveAssignment))
       return true;
     return data().NeedOverloadResolutionForCopyAssignment;
   }
 
   /// Determine whether an implicit copy assignment operator for this
   /// type would have a parameter with a const-qualified reference type.
   bool implicitCopyAssignmentHasConstParam() const {
     return data().ImplicitCopyAssignmentHasConstParam;
   }
 
   /// Determine whether this class has a copy assignment operator with
   /// a parameter type which is a reference to a const-qualified type or is not
   /// a reference.
   bool hasCopyAssignmentWithConstParam() const {
     return data().HasDeclaredCopyAssignmentWithConstParam ||
            (needsImplicitCopyAssignment() &&
             implicitCopyAssignmentHasConstParam());
   }
 
   /// Determine whether this class has had a move assignment
   /// declared by the user.
   bool hasUserDeclaredMoveAssignment() const {
     return data().UserDeclaredSpecialMembers & SMF_MoveAssignment;
   }
 
   /// Determine whether this class has a move assignment operator.
   bool hasMoveAssignment() const {
     return (data().DeclaredSpecialMembers & SMF_MoveAssignment) ||
            needsImplicitMoveAssignment();
   }
 
   /// Set that we attempted to declare an implicit move assignment
   /// operator, but overload resolution failed so we deleted it.
   void setImplicitMoveAssignmentIsDeleted() {
     assert((data().DefaultedMoveAssignmentIsDeleted ||
             needsOverloadResolutionForMoveAssignment()) &&
            "move assignment should not be deleted");
     data().DefaultedMoveAssignmentIsDeleted = true;
   }
 
   /// Determine whether this class should get an implicit move
   /// assignment operator or if any existing special member function inhibits
   /// this.
   bool needsImplicitMoveAssignment() const {
     return !(data().DeclaredSpecialMembers & SMF_MoveAssignment) &&
            !hasUserDeclaredCopyConstructor() &&
            !hasUserDeclaredCopyAssignment() &&
            !hasUserDeclaredMoveConstructor() &&
            !hasUserDeclaredDestructor() &&
            (!isLambda() || lambdaIsDefaultConstructibleAndAssignable());
   }
 
   /// Determine whether we need to eagerly declare a move assignment
   /// operator for this class.
   bool needsOverloadResolutionForMoveAssignment() const {
     return data().NeedOverloadResolutionForMoveAssignment;
   }
 
   /// Determine whether this class has a user-declared destructor.
   ///
   /// When false, a destructor will be implicitly declared.
   bool hasUserDeclaredDestructor() const {
     return data().UserDeclaredSpecialMembers & SMF_Destructor;
   }
 
   /// Determine whether this class needs an implicit destructor to
   /// be lazily declared.
   bool needsImplicitDestructor() const {
     return !(data().DeclaredSpecialMembers & SMF_Destructor);
   }
 
   /// Determine whether we need to eagerly declare a destructor for this
   /// class.
   bool needsOverloadResolutionForDestructor() const {
     return data().NeedOverloadResolutionForDestructor;
   }
 
   /// Determine whether this class describes a lambda function object.
   bool isLambda() const {
     // An update record can't turn a non-lambda into a lambda.
     auto *DD = DefinitionData;
     return DD && DD->IsLambda;
   }
 
   /// Determine whether this class describes a generic
   /// lambda function object (i.e. function call operator is
   /// a template).
   bool isGenericLambda() const;
 
   /// Determine whether this lambda should have an implicit default constructor
   /// and copy and move assignment operators.
   bool lambdaIsDefaultConstructibleAndAssignable() const;
 
   /// Retrieve the lambda call operator of the closure type
   /// if this is a closure type.
   CXXMethodDecl *getLambdaCallOperator() const;
 
   /// Retrieve the dependent lambda call operator of the closure type
   /// if this is a templated closure type.
   FunctionTemplateDecl *getDependentLambdaCallOperator() const;
 
   /// Retrieve the lambda static invoker, the address of which
   /// is returned by the conversion operator, and the body of which
   /// is forwarded to the lambda call operator. The version that does not
   /// take a calling convention uses the 'default' calling convention for free
   /// functions if the Lambda's calling convention was not modified via
   /// attribute. Otherwise, it will return the calling convention specified for
   /// the lambda.
   CXXMethodDecl *getLambdaStaticInvoker() const;
   CXXMethodDecl *getLambdaStaticInvoker(CallingConv CC) const;
 
   /// Retrieve the generic lambda's template parameter list.
   /// Returns null if the class does not represent a lambda or a generic
   /// lambda.
   TemplateParameterList *getGenericLambdaTemplateParameterList() const;
 
   /// Retrieve the lambda template parameters that were specified explicitly.
   ArrayRef<NamedDecl *> getLambdaExplicitTemplateParameters() const;
 
   LambdaCaptureDefault getLambdaCaptureDefault() const {
     assert(isLambda());
     return static_cast<LambdaCaptureDefault>(getLambdaData().CaptureDefault);
   }
 
   bool isCapturelessLambda() const {
     if (!isLambda())
       return false;
     return getLambdaCaptureDefault() == LCD_None && capture_size() == 0;
   }
 
   /// Set the captures for this lambda closure type.
   void setCaptures(ASTContext &Context, ArrayRef<LambdaCapture> Captures);
 
   /// For a closure type, retrieve the mapping from captured
   /// variables and \c this to the non-static data members that store the
   /// values or references of the captures.
   ///
   /// \param Captures Will be populated with the mapping from captured
   /// variables to the corresponding fields.
   ///
   /// \param ThisCapture Will be set to the field declaration for the
   /// \c this capture.
   ///
   /// \note No entries will be added for init-captures, as they do not capture
   /// variables.
   ///
   /// \note If multiple versions of the lambda are merged together, they may
   /// have different variable declarations corresponding to the same capture.
   /// In that case, all of those variable declarations will be added to the
   /// Captures list, so it may have more than one variable listed per field.
   void
   getCaptureFields(llvm::DenseMap<const ValueDecl *, FieldDecl *> &Captures,
                    FieldDecl *&ThisCapture) const;
 
   using capture_const_iterator = const LambdaCapture *;
   using capture_const_range = llvm::iterator_range<capture_const_iterator>;
 
   capture_const_range captures() const {
     return capture_const_range(captures_begin(), captures_end());
   }
 
   capture_const_iterator captures_begin() const {
     if (!isLambda()) return nullptr;
     LambdaDefinitionData &LambdaData = getLambdaData();
     return LambdaData.Captures.empty() ? nullptr : LambdaData.Captures.front();
   }
 
   capture_const_iterator captures_end() const {
     return isLambda() ? captures_begin() + getLambdaData().NumCaptures
                       : nullptr;
   }
 
   unsigned capture_size() const { return getLambdaData().NumCaptures; }
 
   const LambdaCapture *getCapture(unsigned I) const {
     assert(isLambda() && I < capture_size() && "invalid index for capture");
     return captures_begin() + I;
   }
 
   using conversion_iterator = UnresolvedSetIterator;
 
   conversion_iterator conversion_begin() const {
     return data().Conversions.get(getASTContext()).begin();
   }
 
   conversion_iterator conversion_end() const {
     return data().Conversions.get(getASTContext()).end();
   }
 
   /// Removes a conversion function from this class.  The conversion
   /// function must currently be a member of this class.  Furthermore,
   /// this class must currently be in the process of being defined.
   void removeConversion(const NamedDecl *Old);
 
   /// Get all conversion functions visible in current class,
   /// including conversion function templates.
   llvm::iterator_range<conversion_iterator>
   getVisibleConversionFunctions() const;
 
   /// Determine whether this class is an aggregate (C++ [dcl.init.aggr]),
   /// which is a class with no user-declared constructors, no private
   /// or protected non-static data members, no base classes, and no virtual
   /// functions (C++ [dcl.init.aggr]p1).
   bool isAggregate() const { return data().Aggregate; }
 
   /// Whether this class has any in-class initializers
   /// for non-static data members (including those in anonymous unions or
   /// structs).
   bool hasInClassInitializer() const { return data().HasInClassInitializer; }
 
   /// Whether this class or any of its subobjects has any members of
   /// reference type which would make value-initialization ill-formed.
   ///
   /// Per C++03 [dcl.init]p5:
   ///  - if T is a non-union class type without a user-declared constructor,
   ///    then every non-static data member and base-class component of T is
   ///    value-initialized [...] A program that calls for [...]
   ///    value-initialization of an entity of reference type is ill-formed.
   bool hasUninitializedReferenceMember() const {
     return !isUnion() && !hasUserDeclaredConstructor() &&
            data().HasUninitializedReferenceMember;
   }
 
   /// Whether this class is a POD-type (C++ [class]p4)
   ///
   /// For purposes of this function a class is POD if it is an aggregate
   /// that has no non-static non-POD data members, no reference data
   /// members, no user-defined copy assignment operator and no
   /// user-defined destructor.
   ///
   /// Note that this is the C++ TR1 definition of POD.
   bool isPOD() const { return data().PlainOldData; }
 
   /// True if this class is C-like, without C++-specific features, e.g.
   /// it contains only public fields, no bases, tag kind is not 'class', etc.
   bool isCLike() const;
 
   /// Determine whether this is an empty class in the sense of
   /// (C++11 [meta.unary.prop]).
   ///
   /// The CXXRecordDecl is a class type, but not a union type,
   /// with no non-static data members other than bit-fields of length 0,
   /// no virtual member functions, no virtual base classes,
   /// and no base class B for which is_empty<B>::value is false.
   ///
   /// \note This does NOT include a check for union-ness.
   bool isEmpty() const { return data().Empty; }
 
   void setInitMethod(bool Val) { data().HasInitMethod = Val; }
   bool hasInitMethod() const { return data().HasInitMethod; }
 
   bool hasPrivateFields() const {
     return data().HasPrivateFields;
   }
 
   bool hasProtectedFields() const {
     return data().HasProtectedFields;
   }
 
   /// Determine whether this class has direct non-static data members.
   bool hasDirectFields() const {
     auto &D = data();
     return D.HasPublicFields || D.HasProtectedFields || D.HasPrivateFields;
   }
 
   /// If this is a standard-layout class or union, any and all data members will
   /// be declared in the same type.
   ///
   /// This retrieves the type where any fields are declared,
   /// or the current class if there is no class with fields.
   const CXXRecordDecl *getStandardLayoutBaseWithFields() const;
 
   /// Whether this class is polymorphic (C++ [class.virtual]),
   /// which means that the class contains or inherits a virtual function.
   bool isPolymorphic() const { return data().Polymorphic; }
 
   /// Determine whether this class has a pure virtual function.
   ///
   /// The class is abstract per (C++ [class.abstract]p2) if it declares
   /// a pure virtual function or inherits a pure virtual function that is
   /// not overridden.
   bool isAbstract() const { return data().Abstract; }
 
   /// Determine whether this class is standard-layout per
   /// C++ [class]p7.
   bool isStandardLayout() const { return data().IsStandardLayout; }
 
   /// Determine whether this class was standard-layout per
   /// C++11 [class]p7, specifically using the C++11 rules without any DRs.
   bool isCXX11StandardLayout() const { return data().IsCXX11StandardLayout; }
 
   /// Determine whether this class, or any of its class subobjects,
   /// contains a mutable field.
   bool hasMutableFields() const { return data().HasMutableFields; }
 
   /// Determine whether this class has any variant members.
   bool hasVariantMembers() const { return data().HasVariantMembers; }
 
   /// Determine whether this class has a trivial default constructor
   /// (C++11 [class.ctor]p5).
   bool hasTrivialDefaultConstructor() const {
     return hasDefaultConstructor() &&
            (data().HasTrivialSpecialMembers & SMF_DefaultConstructor);
   }
 
   /// Determine whether this class has a non-trivial default constructor
   /// (C++11 [class.ctor]p5).
   bool hasNonTrivialDefaultConstructor() const {
     return (data().DeclaredNonTrivialSpecialMembers & SMF_DefaultConstructor) ||
            (needsImplicitDefaultConstructor() &&
             !(data().HasTrivialSpecialMembers & SMF_DefaultConstructor));
   }
 
   /// Determine whether this class has at least one constexpr constructor
   /// other than the copy or move constructors.
   bool hasConstexprNonCopyMoveConstructor() const {
     return data().HasConstexprNonCopyMoveConstructor ||
            (needsImplicitDefaultConstructor() &&
             defaultedDefaultConstructorIsConstexpr());
   }
 
   /// Determine whether a defaulted default constructor for this class
   /// would be constexpr.
   bool defaultedDefaultConstructorIsConstexpr() const {
     return data().DefaultedDefaultConstructorIsConstexpr &&
            (!isUnion() || hasInClassInitializer() || !hasVariantMembers() ||
             getLangOpts().CPlusPlus20);
   }
 
   /// Determine whether this class has a constexpr default constructor.
   bool hasConstexprDefaultConstructor() const {
     return data().HasConstexprDefaultConstructor ||
            (needsImplicitDefaultConstructor() &&
             defaultedDefaultConstructorIsConstexpr());
   }
 
   /// Determine whether this class has a trivial copy constructor
   /// (C++ [class.copy]p6, C++11 [class.copy]p12)
   bool hasTrivialCopyConstructor() const {
     return data().HasTrivialSpecialMembers & SMF_CopyConstructor;
   }
 
   bool hasTrivialCopyConstructorForCall() const {
     return data().HasTrivialSpecialMembersForCall & SMF_CopyConstructor;
   }
 
   /// Determine whether this class has a non-trivial copy constructor
   /// (C++ [class.copy]p6, C++11 [class.copy]p12)
   bool hasNonTrivialCopyConstructor() const {
     return data().DeclaredNonTrivialSpecialMembers & SMF_CopyConstructor ||
            !hasTrivialCopyConstructor();
   }
 
   bool hasNonTrivialCopyConstructorForCall() const {
     return (data().DeclaredNonTrivialSpecialMembersForCall &
             SMF_CopyConstructor) ||
            !hasTrivialCopyConstructorForCall();
   }
 
   /// Determine whether this class has a trivial move constructor
   /// (C++11 [class.copy]p12)
   bool hasTrivialMoveConstructor() const {
     return hasMoveConstructor() &&
            (data().HasTrivialSpecialMembers & SMF_MoveConstructor);
   }
 
   bool hasTrivialMoveConstructorForCall() const {
     return hasMoveConstructor() &&
            (data().HasTrivialSpecialMembersForCall & SMF_MoveConstructor);
   }
 
   /// Determine whether this class has a non-trivial move constructor
   /// (C++11 [class.copy]p12)
   bool hasNonTrivialMoveConstructor() const {
     return (data().DeclaredNonTrivialSpecialMembers & SMF_MoveConstructor) ||
            (needsImplicitMoveConstructor() &&
             !(data().HasTrivialSpecialMembers & SMF_MoveConstructor));
   }
 
   bool hasNonTrivialMoveConstructorForCall() const {
     return (data().DeclaredNonTrivialSpecialMembersForCall &
             SMF_MoveConstructor) ||
            (needsImplicitMoveConstructor() &&
             !(data().HasTrivialSpecialMembersForCall & SMF_MoveConstructor));
   }
 
   /// Determine whether this class has a trivial copy assignment operator
   /// (C++ [class.copy]p11, C++11 [class.copy]p25)
   bool hasTrivialCopyAssignment() const {
     return data().HasTrivialSpecialMembers & SMF_CopyAssignment;
   }
 
   /// Determine whether this class has a non-trivial copy assignment
   /// operator (C++ [class.copy]p11, C++11 [class.copy]p25)
   bool hasNonTrivialCopyAssignment() const {
     return data().DeclaredNonTrivialSpecialMembers & SMF_CopyAssignment ||
            !hasTrivialCopyAssignment();
   }
 
   /// Determine whether this class has a trivial move assignment operator
   /// (C++11 [class.copy]p25)
   bool hasTrivialMoveAssignment() const {
     return hasMoveAssignment() &&
            (data().HasTrivialSpecialMembers & SMF_MoveAssignment);
   }
 
   /// Determine whether this class has a non-trivial move assignment
   /// operator (C++11 [class.copy]p25)
   bool hasNonTrivialMoveAssignment() const {
     return (data().DeclaredNonTrivialSpecialMembers & SMF_MoveAssignment) ||
            (needsImplicitMoveAssignment() &&
             !(data().HasTrivialSpecialMembers & SMF_MoveAssignment));
   }
 
   /// Determine whether a defaulted default constructor for this class
   /// would be constexpr.
   bool defaultedDestructorIsConstexpr() const {
     return data().DefaultedDestructorIsConstexpr &&
            getLangOpts().CPlusPlus20;
   }
 
   /// Determine whether this class has a constexpr destructor.
   bool hasConstexprDestructor() const;
 
   /// Determine whether this class has a trivial destructor
   /// (C++ [class.dtor]p3)
   bool hasTrivialDestructor() const {
     return data().HasTrivialSpecialMembers & SMF_Destructor;
   }
 
   bool hasTrivialDestructorForCall() const {
     return data().HasTrivialSpecialMembersForCall & SMF_Destructor;
   }
 
   /// Determine whether this class has a non-trivial destructor
   /// (C++ [class.dtor]p3)
   bool hasNonTrivialDestructor() const {
     return !(data().HasTrivialSpecialMembers & SMF_Destructor);
   }
 
   bool hasNonTrivialDestructorForCall() const {
     return !(data().HasTrivialSpecialMembersForCall & SMF_Destructor);
   }
 
   void setHasTrivialSpecialMemberForCall() {
     data().HasTrivialSpecialMembersForCall =
         (SMF_CopyConstructor | SMF_MoveConstructor | SMF_Destructor);
   }
 
   /// Determine whether declaring a const variable with this type is ok
   /// per core issue 253.
   bool allowConstDefaultInit() const {
     return !data().HasUninitializedFields ||
            !(data().HasDefaultedDefaultConstructor ||
              needsImplicitDefaultConstructor());
   }
 
   /// Determine whether this class has a destructor which has no
   /// semantic effect.
   ///
   /// Any such destructor will be trivial, public, defaulted and not deleted,
   /// and will call only irrelevant destructors.
   bool hasIrrelevantDestructor() const {
     return data().HasIrrelevantDestructor;
   }
 
   /// Determine whether this class has a non-literal or/ volatile type
   /// non-static data member or base class.
   bool hasNonLiteralTypeFieldsOrBases() const {
     return data().HasNonLiteralTypeFieldsOrBases;
   }
 
   /// Determine whether this class has a using-declaration that names
   /// a user-declared base class constructor.
   bool hasInheritedConstructor() const {
     return data().HasInheritedConstructor;
   }
 
   /// Determine whether this class has a using-declaration that names
   /// a base class assignment operator.
   bool hasInheritedAssignment() const {
     return data().HasInheritedAssignment;
   }
 
   /// Determine whether this class is considered trivially copyable per
   /// (C++11 [class]p6).
   bool isTriviallyCopyable() const;
 
   /// Determine whether this class is considered trivially copyable per
   bool isTriviallyCopyConstructible() const;
 
   /// Determine whether this class is considered trivial.
   ///
   /// C++11 [class]p6:
   ///    "A trivial class is a class that has a trivial default constructor and
   ///    is trivially copyable."
   bool isTrivial() const {
     return isTriviallyCopyable() && hasTrivialDefaultConstructor();
   }
 
   /// Determine whether this class is a literal type.
   ///
   /// C++20 [basic.types]p10:
   ///   A class type that has all the following properties:
   ///     - it has a constexpr destructor
   ///     - all of its non-static non-variant data members and base classes
   ///       are of non-volatile literal types, and it:
   ///        - is a closure type
   ///        - is an aggregate union type that has either no variant members
   ///          or at least one variant member of non-volatile literal type
   ///        - is a non-union aggregate type for which each of its anonymous
   ///          union members satisfies the above requirements for an aggregate
   ///          union type, or
   ///        - has at least one constexpr constructor or constructor template
   ///          that is not a copy or move constructor.
   bool isLiteral() const;
 
   /// Determine whether this is a structural type.
   bool isStructural() const {
     return isLiteral() && data().StructuralIfLiteral;
   }
 
   /// Notify the class that this destructor is now selected.
   ///
   /// Important properties of the class depend on destructor properties. Since
   /// C++20, it is possible to have multiple destructor declarations in a class
   /// out of which one will be selected at the end.
   /// This is called separately from addedMember because it has to be deferred
   /// to the completion of the class.
   void addedSelectedDestructor(CXXDestructorDecl *DD);
 
   /// Notify the class that an eligible SMF has been added.
   /// This updates triviality and destructor based properties of the class accordingly.
   void addedEligibleSpecialMemberFunction(const CXXMethodDecl *MD, unsigned SMKind);
 
   /// If this record is an instantiation of a member class,
   /// retrieves the member class from which it was instantiated.
   ///
   /// This routine will return non-null for (non-templated) member
   /// classes of class templates. For example, given:
   ///
   /// \code
   /// template<typename T>
   /// struct X {
   ///   struct A { };
   /// };
   /// \endcode
   ///
   /// The declaration for X<int>::A is a (non-templated) CXXRecordDecl
   /// whose parent is the class template specialization X<int>. For
   /// this declaration, getInstantiatedFromMemberClass() will return
   /// the CXXRecordDecl X<T>::A. When a complete definition of
   /// X<int>::A is required, it will be instantiated from the
   /// declaration returned by getInstantiatedFromMemberClass().
   CXXRecordDecl *getInstantiatedFromMemberClass() const;
 
   /// If this class is an instantiation of a member class of a
   /// class template specialization, retrieves the member specialization
   /// information.
   MemberSpecializationInfo *getMemberSpecializationInfo() const;
 
   /// Specify that this record is an instantiation of the
   /// member class \p RD.
   void setInstantiationOfMemberClass(CXXRecordDecl *RD,
                                      TemplateSpecializationKind TSK);
 
   /// Retrieves the class template that is described by this
   /// class declaration.
   ///
   /// Every class template is represented as a ClassTemplateDecl and a
   /// CXXRecordDecl. The former contains template properties (such as
   /// the template parameter lists) while the latter contains the
   /// actual description of the template's
   /// contents. ClassTemplateDecl::getTemplatedDecl() retrieves the
   /// CXXRecordDecl that from a ClassTemplateDecl, while
   /// getDescribedClassTemplate() retrieves the ClassTemplateDecl from
   /// a CXXRecordDecl.
   ClassTemplateDecl *getDescribedClassTemplate() const;
 
   void setDescribedClassTemplate(ClassTemplateDecl *Template);
 
   /// Determine whether this particular class is a specialization or
   /// instantiation of a class template or member class of a class template,
   /// and how it was instantiated or specialized.
   TemplateSpecializationKind getTemplateSpecializationKind() const;
 
   /// Set the kind of specialization or template instantiation this is.
   void setTemplateSpecializationKind(TemplateSpecializationKind TSK);
 
   /// Retrieve the record declaration from which this record could be
   /// instantiated. Returns null if this class is not a template instantiation.
   const CXXRecordDecl *getTemplateInstantiationPattern() const;
 
   CXXRecordDecl *getTemplateInstantiationPattern() {
     return const_cast<CXXRecordDecl *>(const_cast<const CXXRecordDecl *>(this)
                                            ->getTemplateInstantiationPattern());
   }
 
   /// Returns the destructor decl for this class.
   CXXDestructorDecl *getDestructor() const;
 
   /// Returns true if the class destructor, or any implicitly invoked
   /// destructors are marked noreturn.
   bool isAnyDestructorNoReturn() const { return data().IsAnyDestructorNoReturn; }
 
   /// Returns true if the class contains HLSL intangible type, either as
   /// a field or in base class.
   bool isHLSLIntangible() const { return data().IsHLSLIntangible; }
 
   /// If the class is a local class [class.local], returns
   /// the enclosing function declaration.
   const FunctionDecl *isLocalClass() const {
     if (const auto *RD = dyn_cast<CXXRecordDecl>(getDeclContext()))
       return RD->isLocalClass();
 
     return dyn_cast<FunctionDecl>(getDeclContext());
   }
 
   FunctionDecl *isLocalClass() {
     return const_cast<FunctionDecl*>(
         const_cast<const CXXRecordDecl*>(this)->isLocalClass());
   }
 
   /// Determine whether this dependent class is a current instantiation,
   /// when viewed from within the given context.
   bool isCurrentInstantiation(const DeclContext *CurContext) const;
 
   /// Determine whether this class is derived from the class \p Base.
   ///
   /// This routine only determines whether this class is derived from \p Base,
   /// but does not account for factors that may make a Derived -> Base class
   /// ill-formed, such as private/protected inheritance or multiple, ambiguous
   /// base class subobjects.
   ///
   /// \param Base the base class we are searching for.
   ///
   /// \returns true if this class is derived from Base, false otherwise.
   bool isDerivedFrom(const CXXRecordDecl *Base) const;
 
   /// Determine whether this class is derived from the type \p Base.
   ///
   /// This routine only determines whether this class is derived from \p Base,
   /// but does not account for factors that may make a Derived -> Base class
   /// ill-formed, such as private/protected inheritance or multiple, ambiguous
   /// base class subobjects.
   ///
   /// \param Base the base class we are searching for.
   ///
   /// \param Paths will contain the paths taken from the current class to the
   /// given \p Base class.
   ///
   /// \returns true if this class is derived from \p Base, false otherwise.
   ///
   /// \todo add a separate parameter to configure IsDerivedFrom, rather than
   /// tangling input and output in \p Paths
   bool isDerivedFrom(const CXXRecordDecl *Base, CXXBasePaths &Paths) const;
 
   /// Determine whether this class is virtually derived from
   /// the class \p Base.
   ///
   /// This routine only determines whether this class is virtually
   /// derived from \p Base, but does not account for factors that may
   /// make a Derived -> Base class ill-formed, such as
   /// private/protected inheritance or multiple, ambiguous base class
   /// subobjects.
   ///
   /// \param Base the base class we are searching for.
   ///
   /// \returns true if this class is virtually derived from Base,
   /// false otherwise.
   bool isVirtuallyDerivedFrom(const CXXRecordDecl *Base) const;
 
   /// Determine whether this class is provably not derived from
   /// the type \p Base.
   bool isProvablyNotDerivedFrom(const CXXRecordDecl *Base) const;
 
   /// Function type used by forallBases() as a callback.
   ///
   /// \param BaseDefinition the definition of the base class
   ///
   /// \returns true if this base matched the search criteria
   using ForallBasesCallback =
       llvm::function_ref<bool(const CXXRecordDecl *BaseDefinition)>;
 
   /// Determines if the given callback holds for all the direct
   /// or indirect base classes of this type.
   ///
   /// The class itself does not count as a base class.  This routine
   /// returns false if the class has non-computable base classes.
   ///
   /// \param BaseMatches Callback invoked for each (direct or indirect) base
   /// class of this type until a call returns false.
   bool forallBases(ForallBasesCallback BaseMatches) const;
 
   /// Function type used by lookupInBases() to determine whether a
   /// specific base class subobject matches the lookup criteria.
   ///
   /// \param Specifier the base-class specifier that describes the inheritance
   /// from the base class we are trying to match.
   ///
   /// \param Path the current path, from the most-derived class down to the
   /// base named by the \p Specifier.
   ///
   /// \returns true if this base matched the search criteria, false otherwise.
   using BaseMatchesCallback =
       llvm::function_ref<bool(const CXXBaseSpecifier *Specifier,
                               CXXBasePath &Path)>;
 
   /// Look for entities within the base classes of this C++ class,
   /// transitively searching all base class subobjects.
   ///
   /// This routine uses the callback function \p BaseMatches to find base
   /// classes meeting some search criteria, walking all base class subobjects
   /// and populating the given \p Paths structure with the paths through the
   /// inheritance hierarchy that resulted in a match. On a successful search,
   /// the \p Paths structure can be queried to retrieve the matching paths and
   /// to determine if there were any ambiguities.
   ///
   /// \param BaseMatches callback function used to determine whether a given
   /// base matches the user-defined search criteria.
   ///
   /// \param Paths used to record the paths from this class to its base class
   /// subobjects that match the search criteria.
   ///
   /// \param LookupInDependent can be set to true to extend the search to
   /// dependent base classes.
   ///
   /// \returns true if there exists any path from this class to a base class
   /// subobject that matches the search criteria.
   bool lookupInBases(BaseMatchesCallback BaseMatches, CXXBasePaths &Paths,
                      bool LookupInDependent = false) const;
 
   /// Base-class lookup callback that determines whether the given
   /// base class specifier refers to a specific class declaration.
   ///
   /// This callback can be used with \c lookupInBases() to determine whether
   /// a given derived class has is a base class subobject of a particular type.
   /// The base record pointer should refer to the canonical CXXRecordDecl of the
   /// base class that we are searching for.
   static bool FindBaseClass(const CXXBaseSpecifier *Specifier,
                             CXXBasePath &Path, const CXXRecordDecl *BaseRecord);
 
   /// Base-class lookup callback that determines whether the
   /// given base class specifier refers to a specific class
   /// declaration and describes virtual derivation.
   ///
   /// This callback can be used with \c lookupInBases() to determine
   /// whether a given derived class has is a virtual base class
   /// subobject of a particular type.  The base record pointer should
   /// refer to the canonical CXXRecordDecl of the base class that we
   /// are searching for.
   static bool FindVirtualBaseClass(const CXXBaseSpecifier *Specifier,
                                    CXXBasePath &Path,
                                    const CXXRecordDecl *BaseRecord);
 
   /// Retrieve the final overriders for each virtual member
   /// function in the class hierarchy where this class is the
   /// most-derived class in the class hierarchy.
   void getFinalOverriders(CXXFinalOverriderMap &FinaOverriders) const;
 
   /// Get the indirect primary bases for this class.
   void getIndirectPrimaryBases(CXXIndirectPrimaryBaseSet& Bases) const;
 
   /// Determine whether this class has a member with the given name, possibly
   /// in a non-dependent base class.
   ///
   /// No check for ambiguity is performed, so this should never be used when
   /// implementing language semantics, but it may be appropriate for warnings,
   /// static analysis, or similar.
   bool hasMemberName(DeclarationName N) const;
 
   /// Performs an imprecise lookup of a dependent name in this class.
   ///
   /// This function does not follow strict semantic rules and should be used
   /// only when lookup rules can be relaxed, e.g. indexing.
   std::vector<const NamedDecl *>
   lookupDependentName(DeclarationName Name,
                       llvm::function_ref<bool(const NamedDecl *ND)> Filter);
 
   /// Renders and displays an inheritance diagram
   /// for this C++ class and all of its base classes (transitively) using
   /// GraphViz.
   void viewInheritance(ASTContext& Context) const;
 
   /// Calculates the access of a decl that is reached
   /// along a path.
   static AccessSpecifier MergeAccess(AccessSpecifier PathAccess,
                                      AccessSpecifier DeclAccess) {
     assert(DeclAccess != AS_none);
     if (DeclAccess == AS_private) return AS_none;
     return (PathAccess > DeclAccess ? PathAccess : DeclAccess);
   }
 
   /// Indicates that the declaration of a defaulted or deleted special
   /// member function is now complete.
   void finishedDefaultedOrDeletedMember(CXXMethodDecl *MD);
 
   void setTrivialForCallFlags(CXXMethodDecl *MD);
 
   /// Indicates that the definition of this class is now complete.
   void completeDefinition() override;
 
   /// Indicates that the definition of this class is now complete,
   /// and provides a final overrider map to help determine
   ///
   /// \param FinalOverriders The final overrider map for this class, which can
   /// be provided as an optimization for abstract-class checking. If NULL,
   /// final overriders will be computed if they are needed to complete the
   /// definition.
   void completeDefinition(CXXFinalOverriderMap *FinalOverriders);
 
   /// Determine whether this class may end up being abstract, even though
   /// it is not yet known to be abstract.
   ///
   /// \returns true if this class is not known to be abstract but has any
   /// base classes that are abstract. In this case, \c completeDefinition()
   /// will need to compute final overriders to determine whether the class is
   /// actually abstract.
   bool mayBeAbstract() const;
 
   /// Determine whether it's impossible for a class to be derived from this
   /// class. This is best-effort, and may conservatively return false.
   bool isEffectivelyFinal() const;
 
   /// If this is the closure type of a lambda expression, retrieve the
   /// number to be used for name mangling in the Itanium C++ ABI.
   ///
   /// Zero indicates that this closure type has internal linkage, so the
   /// mangling number does not matter, while a non-zero value indicates which
   /// lambda expression this is in this particular context.
   unsigned getLambdaManglingNumber() const {
     assert(isLambda() && "Not a lambda closure type!");
     return getLambdaData().ManglingNumber;
   }
 
   /// The lambda is known to has internal linkage no matter whether it has name
   /// mangling number.
   bool hasKnownLambdaInternalLinkage() const {
     assert(isLambda() && "Not a lambda closure type!");
     return getLambdaData().HasKnownInternalLinkage;
   }
 
   /// Retrieve the declaration that provides additional context for a
   /// lambda, when the normal declaration context is not specific enough.
   ///
   /// Certain contexts (default arguments of in-class function parameters and
   /// the initializers of data members) have separate name mangling rules for
   /// lambdas within the Itanium C++ ABI. For these cases, this routine provides
   /// the declaration in which the lambda occurs, e.g., the function parameter
   /// or the non-static data member. Otherwise, it returns NULL to imply that
   /// the declaration context suffices.
   Decl *getLambdaContextDecl() const;
 
   /// Retrieve the index of this lambda within the context declaration returned
   /// by getLambdaContextDecl().
   unsigned getLambdaIndexInContext() const {
     assert(isLambda() && "Not a lambda closure type!");
     return getLambdaData().IndexInContext;
   }
 
   /// Information about how a lambda is numbered within its context.
   struct LambdaNumbering {
     Decl *ContextDecl = nullptr;
     unsigned IndexInContext = 0;
     unsigned ManglingNumber = 0;
     unsigned DeviceManglingNumber = 0;
     bool HasKnownInternalLinkage = false;
   };
 
   /// Set the mangling numbers and context declaration for a lambda class.
   void setLambdaNumbering(LambdaNumbering Numbering);
 
   // Get the mangling numbers and context declaration for a lambda class.
   LambdaNumbering getLambdaNumbering() const {
     return {getLambdaContextDecl(), getLambdaIndexInContext(),
             getLambdaManglingNumber(), getDeviceLambdaManglingNumber(),
             hasKnownLambdaInternalLinkage()};
   }
 
   /// Retrieve the device side mangling number.
   unsigned getDeviceLambdaManglingNumber() const;
 
   /// Returns the inheritance model used for this record.
   MSInheritanceModel getMSInheritanceModel() const;
 
   /// Calculate what the inheritance model would be for this class.
   MSInheritanceModel calculateInheritanceModel() const;
 
   /// In the Microsoft C++ ABI, use zero for the field offset of a null data
   /// member pointer if we can guarantee that zero is not a valid field offset,
   /// or if the member pointer has multiple fields.  Polymorphic classes have a
   /// vfptr at offset zero, so we can use zero for null.  If there are multiple
   /// fields, we can use zero even if it is a valid field offset because
   /// null-ness testing will check the other fields.
   bool nullFieldOffsetIsZero() const;
 
   /// Controls when vtordisps will be emitted if this record is used as a
   /// virtual base.
   MSVtorDispMode getMSVtorDispMode() const;
 
   /// Determine whether this lambda expression was known to be dependent
   /// at the time it was created, even if its context does not appear to be
   /// dependent.
   ///
   /// This flag is a workaround for an issue with parsing, where default
   /// arguments are parsed before their enclosing function declarations have
   /// been created. This means that any lambda expressions within those
   /// default arguments will have as their DeclContext the context enclosing
   /// the function declaration, which may be non-dependent even when the
   /// function declaration itself is dependent. This flag indicates when we
   /// know that the lambda is dependent despite that.
   bool isDependentLambda() const {
     return isLambda() && getLambdaData().DependencyKind == LDK_AlwaysDependent;
   }
 
   bool isNeverDependentLambda() const {
     return isLambda() && getLambdaData().DependencyKind == LDK_NeverDependent;
   }
 
   unsigned getLambdaDependencyKind() const {
     if (!isLambda())
       return LDK_Unknown;
     return getLambdaData().DependencyKind;
   }
 
   TypeSourceInfo *getLambdaTypeInfo() const {
     return getLambdaData().MethodTyInfo;
   }
 
   void setLambdaTypeInfo(TypeSourceInfo *TS) {
     assert(DefinitionData && DefinitionData->IsLambda &&
            "setting lambda property of non-lambda class");
     auto &DL = static_cast<LambdaDefinitionData &>(*DefinitionData);
     DL.MethodTyInfo = TS;
   }
 
   void setLambdaDependencyKind(unsigned Kind) {
     getLambdaData().DependencyKind = Kind;
   }
 
   void setLambdaIsGeneric(bool IsGeneric) {
     assert(DefinitionData && DefinitionData->IsLambda &&
            "setting lambda property of non-lambda class");
     auto &DL = static_cast<LambdaDefinitionData &>(*DefinitionData);
     DL.IsGenericLambda = IsGeneric;
   }
 
   // Determine whether this type is an Interface Like type for
   // __interface inheritance purposes.
   bool isInterfaceLike() const;
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) {
     return K >= firstCXXRecord && K <= lastCXXRecord;
   }
   void markAbstract() { data().Abstract = true; }
 };
 
 /// Store information needed for an explicit specifier.
 /// Used by CXXDeductionGuideDecl, CXXConstructorDecl and CXXConversionDecl.
 class ExplicitSpecifier {
   llvm::PointerIntPair<Expr *, 2, ExplicitSpecKind> ExplicitSpec{
       nullptr, ExplicitSpecKind::ResolvedFalse};
 
 public:
   ExplicitSpecifier() = default;
   ExplicitSpecifier(Expr *Expression, ExplicitSpecKind Kind)
       : ExplicitSpec(Expression, Kind) {}
   ExplicitSpecKind getKind() const { return ExplicitSpec.getInt(); }
   const Expr *getExpr() const { return ExplicitSpec.getPointer(); }
   Expr *getExpr() { return ExplicitSpec.getPointer(); }
 
   /// Determine if the declaration had an explicit specifier of any kind.
   bool isSpecified() const {
     return ExplicitSpec.getInt() != ExplicitSpecKind::ResolvedFalse ||
            ExplicitSpec.getPointer();
   }
 
   /// Check for equivalence of explicit specifiers.
   /// \return true if the explicit specifier are equivalent, false otherwise.
   bool isEquivalent(const ExplicitSpecifier Other) const;
   /// Determine whether this specifier is known to correspond to an explicit
   /// declaration. Returns false if the specifier is absent or has an
   /// expression that is value-dependent or evaluates to false.
   bool isExplicit() const {
     return ExplicitSpec.getInt() == ExplicitSpecKind::ResolvedTrue;
   }
   /// Determine if the explicit specifier is invalid.
   /// This state occurs after a substitution failures.
   bool isInvalid() const {
     return ExplicitSpec.getInt() == ExplicitSpecKind::Unresolved &&
            !ExplicitSpec.getPointer();
   }
   void setKind(ExplicitSpecKind Kind) { ExplicitSpec.setInt(Kind); }
   void setExpr(Expr *E) { ExplicitSpec.setPointer(E); }
   // Retrieve the explicit specifier in the given declaration, if any.
   static ExplicitSpecifier getFromDecl(FunctionDecl *Function);
   static const ExplicitSpecifier getFromDecl(const FunctionDecl *Function) {
     return getFromDecl(const_cast<FunctionDecl *>(Function));
   }
   static ExplicitSpecifier Invalid() {
     return ExplicitSpecifier(nullptr, ExplicitSpecKind::Unresolved);
   }
 };
 
 /// Represents a C++ deduction guide declaration.
 ///
 /// \code
 /// template<typename T> struct A { A(); A(T); };
 /// A() -> A<int>;
 /// \endcode
 ///
 /// In this example, there will be an explicit deduction guide from the
 /// second line, and implicit deduction guide templates synthesized from
 /// the constructors of \c A.
 class CXXDeductionGuideDecl : public FunctionDecl {
   void anchor() override;
 
 public:
   // Represents the relationship between this deduction guide and the
   // deduction guide that it was generated from (or lack thereof).
   // See the SourceDeductionGuide member for more details.
   enum class SourceDeductionGuideKind : uint8_t {
     None,
     Alias,
   };
 
 private:
   CXXDeductionGuideDecl(ASTContext &C, DeclContext *DC, SourceLocation StartLoc,
                         ExplicitSpecifier ES,
                         const DeclarationNameInfo &NameInfo, QualType T,
                         TypeSourceInfo *TInfo, SourceLocation EndLocation,
                         CXXConstructorDecl *Ctor, DeductionCandidate Kind,
                         Expr *TrailingRequiresClause,
                         const CXXDeductionGuideDecl *GeneratedFrom,
                         SourceDeductionGuideKind SourceKind)
       : FunctionDecl(CXXDeductionGuide, C, DC, StartLoc, NameInfo, T, TInfo,
                      SC_None, false, false, ConstexprSpecKind::Unspecified,
                      TrailingRequiresClause),
         Ctor(Ctor), ExplicitSpec(ES),
         SourceDeductionGuide(GeneratedFrom, SourceKind) {
     if (EndLocation.isValid())
       setRangeEnd(EndLocation);
     setDeductionCandidateKind(Kind);
   }
 
   CXXConstructorDecl *Ctor;
   ExplicitSpecifier ExplicitSpec;
   // The deduction guide, if any, that this deduction guide was generated from,
   // in the case of alias template deduction. The SourceDeductionGuideKind
   // member indicates which of these sources applies, or is None otherwise.
   llvm::PointerIntPair<const CXXDeductionGuideDecl *, 2,
                        SourceDeductionGuideKind>
       SourceDeductionGuide;
   void setExplicitSpecifier(ExplicitSpecifier ES) { ExplicitSpec = ES; }
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   static CXXDeductionGuideDecl *
   Create(ASTContext &C, DeclContext *DC, SourceLocation StartLoc,
          ExplicitSpecifier ES, const DeclarationNameInfo &NameInfo, QualType T,
          TypeSourceInfo *TInfo, SourceLocation EndLocation,
          CXXConstructorDecl *Ctor = nullptr,
          DeductionCandidate Kind = DeductionCandidate::Normal,
          Expr *TrailingRequiresClause = nullptr,
          const CXXDeductionGuideDecl *SourceDG = nullptr,
          SourceDeductionGuideKind SK = SourceDeductionGuideKind::None);
 
   static CXXDeductionGuideDecl *CreateDeserialized(ASTContext &C,
                                                    GlobalDeclID ID);
 
   ExplicitSpecifier getExplicitSpecifier() { return ExplicitSpec; }
   const ExplicitSpecifier getExplicitSpecifier() const { return ExplicitSpec; }
 
   /// Return true if the declaration is already resolved to be explicit.
   bool isExplicit() const { return ExplicitSpec.isExplicit(); }
 
   /// Get the template for which this guide performs deduction.
   TemplateDecl *getDeducedTemplate() const {
     return getDeclName().getCXXDeductionGuideTemplate();
   }
 
   /// Get the constructor from which this deduction guide was generated, if
   /// this is an implicit deduction guide.
   CXXConstructorDecl *getCorrespondingConstructor() const { return Ctor; }
 
   /// Get the deduction guide from which this deduction guide was generated,
   /// if it was generated as part of alias template deduction or from an
   /// inherited constructor.
   const CXXDeductionGuideDecl *getSourceDeductionGuide() const {
     return SourceDeductionGuide.getPointer();
   }
 
   void setSourceDeductionGuide(CXXDeductionGuideDecl *DG) {
     SourceDeductionGuide.setPointer(DG);
   }
 
   SourceDeductionGuideKind getSourceDeductionGuideKind() const {
     return SourceDeductionGuide.getInt();
   }
 
   void setSourceDeductionGuideKind(SourceDeductionGuideKind SK) {
     SourceDeductionGuide.setInt(SK);
   }
 
   void setDeductionCandidateKind(DeductionCandidate K) {
     FunctionDeclBits.DeductionCandidateKind = static_cast<unsigned char>(K);
   }
 
   DeductionCandidate getDeductionCandidateKind() const {
     return static_cast<DeductionCandidate>(
         FunctionDeclBits.DeductionCandidateKind);
   }
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == CXXDeductionGuide; }
 };
 
 /// \brief Represents the body of a requires-expression.
 ///
 /// This decl exists merely to serve as the DeclContext for the local
 /// parameters of the requires expression as well as other declarations inside
 /// it.
 ///
 /// \code
 /// template<typename T> requires requires (T t) { {t++} -> regular; }
 /// \endcode
 ///
 /// In this example, a RequiresExpr object will be generated for the expression,
 /// and a RequiresExprBodyDecl will be created to hold the parameter t and the
 /// template argument list imposed by the compound requirement.
 class RequiresExprBodyDecl : public Decl, public DeclContext {
   RequiresExprBodyDecl(ASTContext &C, DeclContext *DC, SourceLocation StartLoc)
       : Decl(RequiresExprBody, DC, StartLoc), DeclContext(RequiresExprBody) {}
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   static RequiresExprBodyDecl *Create(ASTContext &C, DeclContext *DC,
                                       SourceLocation StartLoc);
 
   static RequiresExprBodyDecl *CreateDeserialized(ASTContext &C,
                                                   GlobalDeclID ID);
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == RequiresExprBody; }
 
   static DeclContext *castToDeclContext(const RequiresExprBodyDecl *D) {
     return static_cast<DeclContext *>(const_cast<RequiresExprBodyDecl *>(D));
   }
 
   static RequiresExprBodyDecl *castFromDeclContext(const DeclContext *DC) {
     return static_cast<RequiresExprBodyDecl *>(const_cast<DeclContext *>(DC));
   }
 };
 
 /// Represents a static or instance method of a struct/union/class.
 ///
 /// In the terminology of the C++ Standard, these are the (static and
 /// non-static) member functions, whether virtual or not.
 class CXXMethodDecl : public FunctionDecl {
   void anchor() override;
 
 protected:
   CXXMethodDecl(Kind DK, ASTContext &C, CXXRecordDecl *RD,
                 SourceLocation StartLoc, const DeclarationNameInfo &NameInfo,
                 QualType T, TypeSourceInfo *TInfo, StorageClass SC,
                 bool UsesFPIntrin, bool isInline,
                 ConstexprSpecKind ConstexprKind, SourceLocation EndLocation,
                 Expr *TrailingRequiresClause = nullptr)
       : FunctionDecl(DK, C, RD, StartLoc, NameInfo, T, TInfo, SC, UsesFPIntrin,
                      isInline, ConstexprKind, TrailingRequiresClause) {
     if (EndLocation.isValid())
       setRangeEnd(EndLocation);
   }
 
 public:
   static CXXMethodDecl *
   Create(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
          const DeclarationNameInfo &NameInfo, QualType T, TypeSourceInfo *TInfo,
          StorageClass SC, bool UsesFPIntrin, bool isInline,
          ConstexprSpecKind ConstexprKind, SourceLocation EndLocation,
          Expr *TrailingRequiresClause = nullptr);
 
   static CXXMethodDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   bool isStatic() const;
   bool isInstance() const { return !isStatic(); }
 
   /// [C++2b][dcl.fct]/p7
   /// An explicit object member function is a non-static
   /// member function with an explicit object parameter. e.g.,
   ///   void func(this SomeType);
   bool isExplicitObjectMemberFunction() const;
 
   /// [C++2b][dcl.fct]/p7
   /// An implicit object member function is a non-static
   /// member function without an explicit object parameter.
   bool isImplicitObjectMemberFunction() const;
 
   /// Returns true if the given operator is implicitly static in a record
   /// context.
   static bool isStaticOverloadedOperator(OverloadedOperatorKind OOK) {
     // [class.free]p1:
     // Any allocation function for a class T is a static member
     // (even if not explicitly declared static).
     // [class.free]p6 Any deallocation function for a class X is a static member
     // (even if not explicitly declared static).
     return OOK == OO_New || OOK == OO_Array_New || OOK == OO_Delete ||
            OOK == OO_Array_Delete;
   }
 
   bool isConst() const { return getType()->castAs<FunctionType>()->isConst(); }
   bool isVolatile() const { return getType()->castAs<FunctionType>()->isVolatile(); }
 
   bool isVirtual() const {
     CXXMethodDecl *CD = const_cast<CXXMethodDecl*>(this)->getCanonicalDecl();
 
     // Member function is virtual if it is marked explicitly so, or if it is
     // declared in __interface -- then it is automatically pure virtual.
     if (CD->isVirtualAsWritten() || CD->isPureVirtual())
       return true;
 
     return CD->size_overridden_methods() != 0;
   }
 
   /// If it's possible to devirtualize a call to this method, return the called
   /// function. Otherwise, return null.
 
   /// \param Base The object on which this virtual function is called.
   /// \param IsAppleKext True if we are compiling for Apple kext.
   CXXMethodDecl *getDevirtualizedMethod(const Expr *Base, bool IsAppleKext);
 
   const CXXMethodDecl *getDevirtualizedMethod(const Expr *Base,
                                               bool IsAppleKext) const {
     return const_cast<CXXMethodDecl *>(this)->getDevirtualizedMethod(
         Base, IsAppleKext);
   }
 
   /// Determine whether this is a usual deallocation function (C++
   /// [basic.stc.dynamic.deallocation]p2), which is an overloaded delete or
   /// delete[] operator with a particular signature. Populates \p PreventedBy
   /// with the declarations of the functions of the same kind if they were the
   /// reason for this function returning false. This is used by
   /// Sema::isUsualDeallocationFunction to reconsider the answer based on the
   /// context.
   bool isUsualDeallocationFunction(
       SmallVectorImpl<const FunctionDecl *> &PreventedBy) const;
 
   /// Determine whether this is a copy-assignment operator, regardless
   /// of whether it was declared implicitly or explicitly.
   bool isCopyAssignmentOperator() const;
 
   /// Determine whether this is a move assignment operator.
   bool isMoveAssignmentOperator() const;
 
   CXXMethodDecl *getCanonicalDecl() override {
     return cast<CXXMethodDecl>(FunctionDecl::getCanonicalDecl());
   }
   const CXXMethodDecl *getCanonicalDecl() const {
     return const_cast<CXXMethodDecl*>(this)->getCanonicalDecl();
   }
 
   CXXMethodDecl *getMostRecentDecl() {
     return cast<CXXMethodDecl>(
             static_cast<FunctionDecl *>(this)->getMostRecentDecl());
   }
   const CXXMethodDecl *getMostRecentDecl() const {
     return const_cast<CXXMethodDecl*>(this)->getMostRecentDecl();
   }
 
   void addOverriddenMethod(const CXXMethodDecl *MD);
 
   using method_iterator = const CXXMethodDecl *const *;
 
   method_iterator begin_overridden_methods() const;
   method_iterator end_overridden_methods() const;
   unsigned size_overridden_methods() const;
 
   using overridden_method_range = llvm::iterator_range<
       llvm::TinyPtrVector<const CXXMethodDecl *>::const_iterator>;
 
   overridden_method_range overridden_methods() const;
 
   /// Return the parent of this method declaration, which
   /// is the class in which this method is defined.
   const CXXRecordDecl *getParent() const {
     return cast<CXXRecordDecl>(FunctionDecl::getParent());
   }
 
   /// Return the parent of this method declaration, which
   /// is the class in which this method is defined.
   CXXRecordDecl *getParent() {
     return const_cast<CXXRecordDecl *>(
              cast<CXXRecordDecl>(FunctionDecl::getParent()));
   }
 
   /// Return the type of the \c this pointer.
   ///
   /// Should only be called for instance (i.e., non-static) methods. Note
   /// that for the call operator of a lambda closure type, this returns the
   /// desugared 'this' type (a pointer to the closure type), not the captured
   /// 'this' type.
   QualType getThisType() const;
 
   /// Return the type of the object pointed by \c this.
   ///
   /// See getThisType() for usage restriction.
 
   QualType getFunctionObjectParameterReferenceType() const;
   QualType getFunctionObjectParameterType() const {
     return getFunctionObjectParameterReferenceType().getNonReferenceType();
   }
 
   unsigned getNumExplicitParams() const {
     return getNumParams() - (isExplicitObjectMemberFunction() ? 1 : 0);
   }
 
   static QualType getThisType(const FunctionProtoType *FPT,
                               const CXXRecordDecl *Decl);
 
   Qualifiers getMethodQualifiers() const {
     return getType()->castAs<FunctionProtoType>()->getMethodQuals();
   }
 
   /// Retrieve the ref-qualifier associated with this method.
   ///
   /// In the following example, \c f() has an lvalue ref-qualifier, \c g()
   /// has an rvalue ref-qualifier, and \c h() has no ref-qualifier.
   /// @code
   /// struct X {
   ///   void f() &;
   ///   void g() &&;
   ///   void h();
   /// };
   /// @endcode
   RefQualifierKind getRefQualifier() const {
     return getType()->castAs<FunctionProtoType>()->getRefQualifier();
   }
 
   bool hasInlineBody() const;
 
   /// Determine whether this is a lambda closure type's static member
   /// function that is used for the result of the lambda's conversion to
   /// function pointer (for a lambda with no captures).
   ///
   /// The function itself, if used, will have a placeholder body that will be
   /// supplied by IR generation to either forward to the function call operator
   /// or clone the function call operator.
   bool isLambdaStaticInvoker() const;
 
   /// Find the method in \p RD that corresponds to this one.
   ///
   /// Find if \p RD or one of the classes it inherits from override this method.
   /// If so, return it. \p RD is assumed to be a subclass of the class defining
   /// this method (or be the class itself), unless \p MayBeBase is set to true.
   CXXMethodDecl *
   getCorrespondingMethodInClass(const CXXRecordDecl *RD,
                                 bool MayBeBase = false);
 
   const CXXMethodDecl *
   getCorrespondingMethodInClass(const CXXRecordDecl *RD,
                                 bool MayBeBase = false) const {
     return const_cast<CXXMethodDecl *>(this)
               ->getCorrespondingMethodInClass(RD, MayBeBase);
   }
 
   /// Find if \p RD declares a function that overrides this function, and if so,
   /// return it. Does not search base classes.
   CXXMethodDecl *getCorrespondingMethodDeclaredInClass(const CXXRecordDecl *RD,
                                                        bool MayBeBase = false);
   const CXXMethodDecl *
   getCorrespondingMethodDeclaredInClass(const CXXRecordDecl *RD,
                                         bool MayBeBase = false) const {
     return const_cast<CXXMethodDecl *>(this)
         ->getCorrespondingMethodDeclaredInClass(RD, MayBeBase);
   }
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) {
     return K >= firstCXXMethod && K <= lastCXXMethod;
   }
 };
 
 /// Represents a C++ base or member initializer.
 ///
 /// This is part of a constructor initializer that
 /// initializes one non-static member variable or one base class. For
 /// example, in the following, both 'A(a)' and 'f(3.14159)' are member
 /// initializers:
 ///
 /// \code
 /// class A { };
 /// class B : public A {
 ///   float f;
 /// public:
 ///   B(A& a) : A(a), f(3.14159) { }
 /// };
 /// \endcode
 class CXXCtorInitializer final {
   /// Either the base class name/delegating constructor type (stored as
   /// a TypeSourceInfo*), an normal field (FieldDecl), or an anonymous field
   /// (IndirectFieldDecl*) being initialized.
   llvm::PointerUnion<TypeSourceInfo *, FieldDecl *, IndirectFieldDecl *>
       Initializee;
 
   /// The argument used to initialize the base or member, which may
   /// end up constructing an object (when multiple arguments are involved).
   Stmt *Init;
 
   /// The source location for the field name or, for a base initializer
   /// pack expansion, the location of the ellipsis.
   ///
   /// In the case of a delegating
   /// constructor, it will still include the type's source location as the
   /// Initializee points to the CXXConstructorDecl (to allow loop detection).
   SourceLocation MemberOrEllipsisLocation;
 
   /// Location of the left paren of the ctor-initializer.
   SourceLocation LParenLoc;
 
   /// Location of the right paren of the ctor-initializer.
   SourceLocation RParenLoc;
 
   /// If the initializee is a type, whether that type makes this
   /// a delegating initialization.
   LLVM_PREFERRED_TYPE(bool)
   unsigned IsDelegating : 1;
 
   /// If the initializer is a base initializer, this keeps track
   /// of whether the base is virtual or not.
   LLVM_PREFERRED_TYPE(bool)
   unsigned IsVirtual : 1;
 
   /// Whether or not the initializer is explicitly written
   /// in the sources.
   LLVM_PREFERRED_TYPE(bool)
   unsigned IsWritten : 1;
 
   /// If IsWritten is true, then this number keeps track of the textual order
   /// of this initializer in the original sources, counting from 0.
   unsigned SourceOrder : 13;
 
 public:
   /// Creates a new base-class initializer.
   explicit
   CXXCtorInitializer(ASTContext &Context, TypeSourceInfo *TInfo, bool IsVirtual,
                      SourceLocation L, Expr *Init, SourceLocation R,
                      SourceLocation EllipsisLoc);
 
   /// Creates a new member initializer.
   explicit
   CXXCtorInitializer(ASTContext &Context, FieldDecl *Member,
                      SourceLocation MemberLoc, SourceLocation L, Expr *Init,
                      SourceLocation R);
 
   /// Creates a new anonymous field initializer.
   explicit
   CXXCtorInitializer(ASTContext &Context, IndirectFieldDecl *Member,
                      SourceLocation MemberLoc, SourceLocation L, Expr *Init,
                      SourceLocation R);
 
   /// Creates a new delegating initializer.
   explicit
   CXXCtorInitializer(ASTContext &Context, TypeSourceInfo *TInfo,
                      SourceLocation L, Expr *Init, SourceLocation R);
 
   /// \return Unique reproducible object identifier.
   int64_t getID(const ASTContext &Context) const;
 
   /// Determine whether this initializer is initializing a base class.
   bool isBaseInitializer() const {
     return isa<TypeSourceInfo *>(Initializee) && !IsDelegating;
   }
 
   /// Determine whether this initializer is initializing a non-static
   /// data member.
   bool isMemberInitializer() const { return isa<FieldDecl *>(Initializee); }
 
   bool isAnyMemberInitializer() const {
     return isMemberInitializer() || isIndirectMemberInitializer();
   }
 
   bool isIndirectMemberInitializer() const {
     return isa<IndirectFieldDecl *>(Initializee);
   }
 
   /// Determine whether this initializer is an implicit initializer
   /// generated for a field with an initializer defined on the member
   /// declaration.
   ///
   /// In-class member initializers (also known as "non-static data member
   /// initializations", NSDMIs) were introduced in C++11.
   bool isInClassMemberInitializer() const {
     return Init->getStmtClass() == Stmt::CXXDefaultInitExprClass;
   }
 
   /// Determine whether this initializer is creating a delegating
   /// constructor.
   bool isDelegatingInitializer() const {
     return isa<TypeSourceInfo *>(Initializee) && IsDelegating;
   }
 
   /// Determine whether this initializer is a pack expansion.
   bool isPackExpansion() const {
     return isBaseInitializer() && MemberOrEllipsisLocation.isValid();
   }
 
   // For a pack expansion, returns the location of the ellipsis.
   SourceLocation getEllipsisLoc() const {
     if (!isPackExpansion())
       return {};
     return MemberOrEllipsisLocation;
   }
 
   /// If this is a base class initializer, returns the type of the
   /// base class with location information. Otherwise, returns an NULL
   /// type location.
   TypeLoc getBaseClassLoc() const;
 
   /// If this is a base class initializer, returns the type of the base class.
   /// Otherwise, returns null.
   const Type *getBaseClass() const;
 
   /// Returns whether the base is virtual or not.
   bool isBaseVirtual() const {
     assert(isBaseInitializer() && "Must call this on base initializer!");
 
     return IsVirtual;
   }
 
   /// Returns the declarator information for a base class or delegating
   /// initializer.
   TypeSourceInfo *getTypeSourceInfo() const {
     return Initializee.dyn_cast<TypeSourceInfo *>();
   }
 
   /// If this is a member initializer, returns the declaration of the
   /// non-static data member being initialized. Otherwise, returns null.
   FieldDecl *getMember() const {
     if (isMemberInitializer())
       return cast<FieldDecl *>(Initializee);
     return nullptr;
   }
 
   FieldDecl *getAnyMember() const {
     if (isMemberInitializer())
       return cast<FieldDecl *>(Initializee);
     if (isIndirectMemberInitializer())
       return cast<IndirectFieldDecl *>(Initializee)->getAnonField();
     return nullptr;
   }
 
   IndirectFieldDecl *getIndirectMember() const {
     if (isIndirectMemberInitializer())
       return cast<IndirectFieldDecl *>(Initializee);
     return nullptr;
   }
 
   SourceLocation getMemberLocation() const {
     return MemberOrEllipsisLocation;
   }
 
   /// Determine the source location of the initializer.
   SourceLocation getSourceLocation() const;
 
   /// Determine the source range covering the entire initializer.
   SourceRange getSourceRange() const LLVM_READONLY;
 
   /// Determine whether this initializer is explicitly written
   /// in the source code.
   bool isWritten() const { return IsWritten; }
 
   /// Return the source position of the initializer, counting from 0.
   /// If the initializer was implicit, -1 is returned.
   int getSourceOrder() const {
     return IsWritten ? static_cast<int>(SourceOrder) : -1;
   }
 
   /// Set the source order of this initializer.
   ///
   /// This can only be called once for each initializer; it cannot be called
   /// on an initializer having a positive number of (implicit) array indices.
   ///
   /// This assumes that the initializer was written in the source code, and
   /// ensures that isWritten() returns true.
   void setSourceOrder(int Pos) {
     assert(!IsWritten &&
            "setSourceOrder() used on implicit initializer");
     assert(SourceOrder == 0 &&
            "calling twice setSourceOrder() on the same initializer");
     assert(Pos >= 0 &&
            "setSourceOrder() used to make an initializer implicit");
     IsWritten = true;
     SourceOrder = static_cast<unsigned>(Pos);
   }
 
   SourceLocation getLParenLoc() const { return LParenLoc; }
   SourceLocation getRParenLoc() const { return RParenLoc; }
 
   /// Get the initializer.
   Expr *getInit() const { return static_cast<Expr *>(Init); }
 };
 
 /// Description of a constructor that was inherited from a base class.
 class InheritedConstructor {
   ConstructorUsingShadowDecl *Shadow = nullptr;
   CXXConstructorDecl *BaseCtor = nullptr;
 
 public:
   InheritedConstructor() = default;
   InheritedConstructor(ConstructorUsingShadowDecl *Shadow,
                        CXXConstructorDecl *BaseCtor)
       : Shadow(Shadow), BaseCtor(BaseCtor) {}
 
   explicit operator bool() const { return Shadow; }
 
   ConstructorUsingShadowDecl *getShadowDecl() const { return Shadow; }
   CXXConstructorDecl *getConstructor() const { return BaseCtor; }
 };
 
 /// Represents a C++ constructor within a class.
 ///
 /// For example:
 ///
 /// \code
 /// class X {
 /// public:
 ///   explicit X(int); // represented by a CXXConstructorDecl.
 /// };
 /// \endcode
 class CXXConstructorDecl final
     : public CXXMethodDecl,
       private llvm::TrailingObjects<CXXConstructorDecl, InheritedConstructor,
                                     ExplicitSpecifier> {
   // This class stores some data in DeclContext::CXXConstructorDeclBits
   // to save some space. Use the provided accessors to access it.
 
   /// \name Support for base and member initializers.
   /// \{
   /// The arguments used to initialize the base or member.
   LazyCXXCtorInitializersPtr CtorInitializers;
 
   CXXConstructorDecl(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
                      const DeclarationNameInfo &NameInfo, QualType T,
                      TypeSourceInfo *TInfo, ExplicitSpecifier ES,
                      bool UsesFPIntrin, bool isInline,
                      bool isImplicitlyDeclared, ConstexprSpecKind ConstexprKind,
                      InheritedConstructor Inherited,
                      Expr *TrailingRequiresClause);
 
   void anchor() override;
 
   size_t numTrailingObjects(OverloadToken<InheritedConstructor>) const {
     return CXXConstructorDeclBits.IsInheritingConstructor;
   }
   size_t numTrailingObjects(OverloadToken<ExplicitSpecifier>) const {
     return CXXConstructorDeclBits.HasTrailingExplicitSpecifier;
   }
 
   ExplicitSpecifier getExplicitSpecifierInternal() const {
     if (CXXConstructorDeclBits.HasTrailingExplicitSpecifier)
       return *getTrailingObjects<ExplicitSpecifier>();
     return ExplicitSpecifier(
         nullptr, CXXConstructorDeclBits.IsSimpleExplicit
                      ? ExplicitSpecKind::ResolvedTrue
                      : ExplicitSpecKind::ResolvedFalse);
   }
 
   enum TrailingAllocKind {
     TAKInheritsConstructor = 1,
     TAKHasTailExplicit = 1 << 1,
   };
 
   uint64_t getTrailingAllocKind() const {
     return numTrailingObjects(OverloadToken<InheritedConstructor>()) |
            (numTrailingObjects(OverloadToken<ExplicitSpecifier>()) << 1);
   }
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
   friend TrailingObjects;
 
   static CXXConstructorDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID,
                                                 uint64_t AllocKind);
   static CXXConstructorDecl *
   Create(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
          const DeclarationNameInfo &NameInfo, QualType T, TypeSourceInfo *TInfo,
          ExplicitSpecifier ES, bool UsesFPIntrin, bool isInline,
          bool isImplicitlyDeclared, ConstexprSpecKind ConstexprKind,
          InheritedConstructor Inherited = InheritedConstructor(),
          Expr *TrailingRequiresClause = nullptr);
 
   void setExplicitSpecifier(ExplicitSpecifier ES) {
     assert((!ES.getExpr() ||
             CXXConstructorDeclBits.HasTrailingExplicitSpecifier) &&
            "cannot set this explicit specifier. no trail-allocated space for "
            "explicit");
     if (ES.getExpr())
       *getCanonicalDecl()->getTrailingObjects<ExplicitSpecifier>() = ES;
     else
       CXXConstructorDeclBits.IsSimpleExplicit = ES.isExplicit();
   }
 
   ExplicitSpecifier getExplicitSpecifier() {
     return getCanonicalDecl()->getExplicitSpecifierInternal();
   }
   const ExplicitSpecifier getExplicitSpecifier() const {
     return getCanonicalDecl()->getExplicitSpecifierInternal();
   }
 
   /// Return true if the declaration is already resolved to be explicit.
   bool isExplicit() const { return getExplicitSpecifier().isExplicit(); }
 
   /// Iterates through the member/base initializer list.
   using init_iterator = CXXCtorInitializer **;
 
   /// Iterates through the member/base initializer list.
   using init_const_iterator = CXXCtorInitializer *const *;
 
   using init_range = llvm::iterator_range<init_iterator>;
   using init_const_range = llvm::iterator_range<init_const_iterator>;
 
   init_range inits() { return init_range(init_begin(), init_end()); }
   init_const_range inits() const {
     return init_const_range(init_begin(), init_end());
   }
 
   /// Retrieve an iterator to the first initializer.
   init_iterator init_begin() {
     const auto *ConstThis = this;
     return const_cast<init_iterator>(ConstThis->init_begin());
   }
 
   /// Retrieve an iterator to the first initializer.
   init_const_iterator init_begin() const;
 
   /// Retrieve an iterator past the last initializer.
   init_iterator       init_end()       {
     return init_begin() + getNumCtorInitializers();
   }
 
   /// Retrieve an iterator past the last initializer.
   init_const_iterator init_end() const {
     return init_begin() + getNumCtorInitializers();
   }
 
   using init_reverse_iterator = std::reverse_iterator<init_iterator>;
   using init_const_reverse_iterator =
       std::reverse_iterator<init_const_iterator>;
 
   init_reverse_iterator init_rbegin() {
     return init_reverse_iterator(init_end());
   }
   init_const_reverse_iterator init_rbegin() const {
     return init_const_reverse_iterator(init_end());
   }
 
   init_reverse_iterator init_rend() {
     return init_reverse_iterator(init_begin());
   }
   init_const_reverse_iterator init_rend() const {
     return init_const_reverse_iterator(init_begin());
   }
 
   /// Determine the number of arguments used to initialize the member
   /// or base.
   unsigned getNumCtorInitializers() const {
       return CXXConstructorDeclBits.NumCtorInitializers;
   }
 
   void setNumCtorInitializers(unsigned numCtorInitializers) {
     CXXConstructorDeclBits.NumCtorInitializers = numCtorInitializers;
     // This assert added because NumCtorInitializers is stored
     // in CXXConstructorDeclBits as a bitfield and its width has
     // been shrunk from 32 bits to fit into CXXConstructorDeclBitfields.
     assert(CXXConstructorDeclBits.NumCtorInitializers ==
            numCtorInitializers && "NumCtorInitializers overflow!");
   }
 
   void setCtorInitializers(CXXCtorInitializer **Initializers) {
     CtorInitializers = Initializers;
   }
 
   /// Determine whether this constructor is a delegating constructor.
   bool isDelegatingConstructor() const {
     return (getNumCtorInitializers() == 1) &&
            init_begin()[0]->isDelegatingInitializer();
   }
 
   /// When this constructor delegates to another, retrieve the target.
   CXXConstructorDecl *getTargetConstructor() const;
 
   /// Whether this constructor is a default
   /// constructor (C++ [class.ctor]p5), which can be used to
   /// default-initialize a class of this type.
   bool isDefaultConstructor() const;
 
   /// Whether this constructor is a copy constructor (C++ [class.copy]p2,
   /// which can be used to copy the class.
   ///
   /// \p TypeQuals will be set to the qualifiers on the
   /// argument type. For example, \p TypeQuals would be set to \c
   /// Qualifiers::Const for the following copy constructor:
   ///
   /// \code
   /// class X {
   /// public:
   ///   X(const X&);
   /// };
   /// \endcode
   bool isCopyConstructor(unsigned &TypeQuals) const;
 
   /// Whether this constructor is a copy
   /// constructor (C++ [class.copy]p2, which can be used to copy the
   /// class.
   bool isCopyConstructor() const {
     unsigned TypeQuals = 0;
     return isCopyConstructor(TypeQuals);
   }
 
   /// Determine whether this constructor is a move constructor
   /// (C++11 [class.copy]p3), which can be used to move values of the class.
   ///
   /// \param TypeQuals If this constructor is a move constructor, will be set
   /// to the type qualifiers on the referent of the first parameter's type.
   bool isMoveConstructor(unsigned &TypeQuals) const;
 
   /// Determine whether this constructor is a move constructor
   /// (C++11 [class.copy]p3), which can be used to move values of the class.
   bool isMoveConstructor() const {
     unsigned TypeQuals = 0;
     return isMoveConstructor(TypeQuals);
   }
 
   /// Determine whether this is a copy or move constructor.
   ///
   /// \param TypeQuals Will be set to the type qualifiers on the reference
   /// parameter, if in fact this is a copy or move constructor.
   bool isCopyOrMoveConstructor(unsigned &TypeQuals) const;
 
   /// Determine whether this a copy or move constructor.
   bool isCopyOrMoveConstructor() const {
     unsigned Quals;
     return isCopyOrMoveConstructor(Quals);
   }
 
   /// Whether this constructor is a
   /// converting constructor (C++ [class.conv.ctor]), which can be
   /// used for user-defined conversions.
   bool isConvertingConstructor(bool AllowExplicit) const;
 
   /// Determine whether this is a member template specialization that
   /// would copy the object to itself. Such constructors are never used to copy
   /// an object.
   bool isSpecializationCopyingObject() const;
 
   /// Determine whether this is an implicit constructor synthesized to
   /// model a call to a constructor inherited from a base class.
   bool isInheritingConstructor() const {
     return CXXConstructorDeclBits.IsInheritingConstructor;
   }
 
   /// State that this is an implicit constructor synthesized to
   /// model a call to a constructor inherited from a base class.
   void setInheritingConstructor(bool isIC = true) {
     CXXConstructorDeclBits.IsInheritingConstructor = isIC;
   }
 
   /// Get the constructor that this inheriting constructor is based on.
   InheritedConstructor getInheritedConstructor() const {
     return isInheritingConstructor() ?
       *getTrailingObjects<InheritedConstructor>() : InheritedConstructor();
   }
 
   CXXConstructorDecl *getCanonicalDecl() override {
     return cast<CXXConstructorDecl>(FunctionDecl::getCanonicalDecl());
   }
   const CXXConstructorDecl *getCanonicalDecl() const {
     return const_cast<CXXConstructorDecl*>(this)->getCanonicalDecl();
   }
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == CXXConstructor; }
 };
 
 /// Represents a C++ destructor within a class.
 ///
 /// For example:
 ///
 /// \code
 /// class X {
 /// public:
 ///   ~X(); // represented by a CXXDestructorDecl.
 /// };
 /// \endcode
 class CXXDestructorDecl : public CXXMethodDecl {
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   // FIXME: Don't allocate storage for these except in the first declaration
   // of a virtual destructor.
   FunctionDecl *OperatorDelete = nullptr;
   Expr *OperatorDeleteThisArg = nullptr;
 
   CXXDestructorDecl(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
                     const DeclarationNameInfo &NameInfo, QualType T,
                     TypeSourceInfo *TInfo, bool UsesFPIntrin, bool isInline,
                     bool isImplicitlyDeclared, ConstexprSpecKind ConstexprKind,
                     Expr *TrailingRequiresClause = nullptr)
       : CXXMethodDecl(CXXDestructor, C, RD, StartLoc, NameInfo, T, TInfo,
                       SC_None, UsesFPIntrin, isInline, ConstexprKind,
                       SourceLocation(), TrailingRequiresClause) {
     setImplicit(isImplicitlyDeclared);
   }
 
   void anchor() override;
 
 public:
   static CXXDestructorDecl *
   Create(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
          const DeclarationNameInfo &NameInfo, QualType T, TypeSourceInfo *TInfo,
          bool UsesFPIntrin, bool isInline, bool isImplicitlyDeclared,
          ConstexprSpecKind ConstexprKind,
          Expr *TrailingRequiresClause = nullptr);
   static CXXDestructorDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   void setOperatorDelete(FunctionDecl *OD, Expr *ThisArg);
 
   const FunctionDecl *getOperatorDelete() const {
     return getCanonicalDecl()->OperatorDelete;
   }
 
   Expr *getOperatorDeleteThisArg() const {
     return getCanonicalDecl()->OperatorDeleteThisArg;
   }
 
   /// Will this destructor ever be called when considering which deallocation
   /// function is associated with the destructor? Can optionally be passed an
   /// 'operator delete' function declaration to test against specifically.
   bool isCalledByDelete(const FunctionDecl *OpDel = nullptr) const;
 
   CXXDestructorDecl *getCanonicalDecl() override {
     return cast<CXXDestructorDecl>(FunctionDecl::getCanonicalDecl());
   }
   const CXXDestructorDecl *getCanonicalDecl() const {
     return const_cast<CXXDestructorDecl*>(this)->getCanonicalDecl();
   }
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == CXXDestructor; }
 };
 
 /// Represents a C++ conversion function within a class.
 ///
 /// For example:
 ///
 /// \code
 /// class X {
 /// public:
 ///   operator bool();
 /// };
 /// \endcode
 class CXXConversionDecl : public CXXMethodDecl {
   CXXConversionDecl(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
                     const DeclarationNameInfo &NameInfo, QualType T,
                     TypeSourceInfo *TInfo, bool UsesFPIntrin, bool isInline,
                     ExplicitSpecifier ES, ConstexprSpecKind ConstexprKind,
                     SourceLocation EndLocation,
                     Expr *TrailingRequiresClause = nullptr)
       : CXXMethodDecl(CXXConversion, C, RD, StartLoc, NameInfo, T, TInfo,
                       SC_None, UsesFPIntrin, isInline, ConstexprKind,
                       EndLocation, TrailingRequiresClause),
         ExplicitSpec(ES) {}
   void anchor() override;
 
   ExplicitSpecifier ExplicitSpec;
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   static CXXConversionDecl *
   Create(ASTContext &C, CXXRecordDecl *RD, SourceLocation StartLoc,
          const DeclarationNameInfo &NameInfo, QualType T, TypeSourceInfo *TInfo,
          bool UsesFPIntrin, bool isInline, ExplicitSpecifier ES,
          ConstexprSpecKind ConstexprKind, SourceLocation EndLocation,
          Expr *TrailingRequiresClause = nullptr);
   static CXXConversionDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   ExplicitSpecifier getExplicitSpecifier() {
     return getCanonicalDecl()->ExplicitSpec;
   }
 
   const ExplicitSpecifier getExplicitSpecifier() const {
     return getCanonicalDecl()->ExplicitSpec;
   }
 
   /// Return true if the declaration is already resolved to be explicit.
   bool isExplicit() const { return getExplicitSpecifier().isExplicit(); }
   void setExplicitSpecifier(ExplicitSpecifier ES) { ExplicitSpec = ES; }
 
   /// Returns the type that this conversion function is converting to.
   QualType getConversionType() const {
     return getType()->castAs<FunctionType>()->getReturnType();
   }
 
   /// Determine whether this conversion function is a conversion from
   /// a lambda closure type to a block pointer.
   bool isLambdaToBlockPointerConversion() const;
 
   CXXConversionDecl *getCanonicalDecl() override {
     return cast<CXXConversionDecl>(FunctionDecl::getCanonicalDecl());
   }
   const CXXConversionDecl *getCanonicalDecl() const {
     return const_cast<CXXConversionDecl*>(this)->getCanonicalDecl();
   }
 
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == CXXConversion; }
 };
 
 /// Represents the language in a linkage specification.
 ///
 /// The values are part of the serialization ABI for
 /// ASTs and cannot be changed without altering that ABI.
 enum class LinkageSpecLanguageIDs { C = 1, CXX = 2 };
 
 /// Represents a linkage specification.
 ///
 /// For example:
 /// \code
 ///   extern "C" void foo();
 /// \endcode
 class LinkageSpecDecl : public Decl, public DeclContext {
   virtual void anchor();
   // This class stores some data in DeclContext::LinkageSpecDeclBits to save
   // some space. Use the provided accessors to access it.
 
   /// The source location for the extern keyword.
   SourceLocation ExternLoc;
 
   /// The source location for the right brace (if valid).
   SourceLocation RBraceLoc;
 
   LinkageSpecDecl(DeclContext *DC, SourceLocation ExternLoc,
                   SourceLocation LangLoc, LinkageSpecLanguageIDs lang,
                   bool HasBraces);
 
 public:
   static LinkageSpecDecl *Create(ASTContext &C, DeclContext *DC,
                                  SourceLocation ExternLoc,
                                  SourceLocation LangLoc,
                                  LinkageSpecLanguageIDs Lang, bool HasBraces);
   static LinkageSpecDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   /// Return the language specified by this linkage specification.
   LinkageSpecLanguageIDs getLanguage() const {
     return static_cast<LinkageSpecLanguageIDs>(LinkageSpecDeclBits.Language);
   }
 
   /// Set the language specified by this linkage specification.
   void setLanguage(LinkageSpecLanguageIDs L) {
     LinkageSpecDeclBits.Language = llvm::to_underlying(L);
   }
 
   /// Determines whether this linkage specification had braces in
   /// its syntactic form.
   bool hasBraces() const {
     assert(!RBraceLoc.isValid() || LinkageSpecDeclBits.HasBraces);
     return LinkageSpecDeclBits.HasBraces;
   }
 
   SourceLocation getExternLoc() const { return ExternLoc; }
   SourceLocation getRBraceLoc() const { return RBraceLoc; }
   void setExternLoc(SourceLocation L) { ExternLoc = L; }
   void setRBraceLoc(SourceLocation L) {
     RBraceLoc = L;
     LinkageSpecDeclBits.HasBraces = RBraceLoc.isValid();
   }
 
   SourceLocation getEndLoc() const LLVM_READONLY {
     if (hasBraces())
       return getRBraceLoc();
     // No braces: get the end location of the (only) declaration in context
     // (if present).
     return decls_empty() ? getLocation() : decls_begin()->getEndLoc();
   }
 
   SourceRange getSourceRange() const override LLVM_READONLY {
     return SourceRange(ExternLoc, getEndLoc());
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == LinkageSpec; }
 
   static DeclContext *castToDeclContext(const LinkageSpecDecl *D) {
     return static_cast<DeclContext *>(const_cast<LinkageSpecDecl*>(D));
   }
 
   static LinkageSpecDecl *castFromDeclContext(const DeclContext *DC) {
     return static_cast<LinkageSpecDecl *>(const_cast<DeclContext*>(DC));
   }
 };
 
 /// Represents C++ using-directive.
 ///
 /// For example:
 /// \code
 ///    using namespace std;
 /// \endcode
 ///
 /// \note UsingDirectiveDecl should be Decl not NamedDecl, but we provide
 /// artificial names for all using-directives in order to store
 /// them in DeclContext effectively.
 class UsingDirectiveDecl : public NamedDecl {
   /// The location of the \c using keyword.
   SourceLocation UsingLoc;
 
   /// The location of the \c namespace keyword.
   SourceLocation NamespaceLoc;
 
   /// The nested-name-specifier that precedes the namespace.
   NestedNameSpecifierLoc QualifierLoc;
 
   /// The namespace nominated by this using-directive.
   NamedDecl *NominatedNamespace;
 
   /// Enclosing context containing both using-directive and nominated
   /// namespace.
   DeclContext *CommonAncestor;
 
   UsingDirectiveDecl(DeclContext *DC, SourceLocation UsingLoc,
                      SourceLocation NamespcLoc,
                      NestedNameSpecifierLoc QualifierLoc,
                      SourceLocation IdentLoc,
                      NamedDecl *Nominated,
                      DeclContext *CommonAncestor)
       : NamedDecl(UsingDirective, DC, IdentLoc, getName()), UsingLoc(UsingLoc),
         NamespaceLoc(NamespcLoc), QualifierLoc(QualifierLoc),
         NominatedNamespace(Nominated), CommonAncestor(CommonAncestor) {}
 
   /// Returns special DeclarationName used by using-directives.
   ///
   /// This is only used by DeclContext for storing UsingDirectiveDecls in
   /// its lookup structure.
   static DeclarationName getName() {
     return DeclarationName::getUsingDirectiveName();
   }
 
   void anchor() override;
 
 public:
   friend class ASTDeclReader;
 
   // Friend for getUsingDirectiveName.
   friend class DeclContext;
 
   /// Retrieve the nested-name-specifier that qualifies the
   /// name of the namespace, with source-location information.
   NestedNameSpecifierLoc getQualifierLoc() const { return QualifierLoc; }
 
   /// Retrieve the nested-name-specifier that qualifies the
   /// name of the namespace.
   NestedNameSpecifier *getQualifier() const {
     return QualifierLoc.getNestedNameSpecifier();
   }
 
   NamedDecl *getNominatedNamespaceAsWritten() { return NominatedNamespace; }
   const NamedDecl *getNominatedNamespaceAsWritten() const {
     return NominatedNamespace;
   }
 
   /// Returns the namespace nominated by this using-directive.
   NamespaceDecl *getNominatedNamespace();
 
   const NamespaceDecl *getNominatedNamespace() const {
     return const_cast<UsingDirectiveDecl*>(this)->getNominatedNamespace();
   }
 
   /// Returns the common ancestor context of this using-directive and
   /// its nominated namespace.
   DeclContext *getCommonAncestor() { return CommonAncestor; }
   const DeclContext *getCommonAncestor() const { return CommonAncestor; }
 
   /// Return the location of the \c using keyword.
   SourceLocation getUsingLoc() const { return UsingLoc; }
 
   // FIXME: Could omit 'Key' in name.
   /// Returns the location of the \c namespace keyword.
   SourceLocation getNamespaceKeyLocation() const { return NamespaceLoc; }
 
   /// Returns the location of this using declaration's identifier.
   SourceLocation getIdentLocation() const { return getLocation(); }
 
   static UsingDirectiveDecl *Create(ASTContext &C, DeclContext *DC,
                                     SourceLocation UsingLoc,
                                     SourceLocation NamespaceLoc,
                                     NestedNameSpecifierLoc QualifierLoc,
                                     SourceLocation IdentLoc,
                                     NamedDecl *Nominated,
                                     DeclContext *CommonAncestor);
   static UsingDirectiveDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   SourceRange getSourceRange() const override LLVM_READONLY {
     return SourceRange(UsingLoc, getLocation());
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == UsingDirective; }
 };
 
 /// Represents a C++ namespace alias.
 ///
 /// For example:
 ///
 /// \code
 /// namespace Foo = Bar;
 /// \endcode
 class NamespaceAliasDecl : public NamedDecl,
                            public Redeclarable<NamespaceAliasDecl> {
   friend class ASTDeclReader;
 
   /// The location of the \c namespace keyword.
   SourceLocation NamespaceLoc;
 
   /// The location of the namespace's identifier.
   ///
   /// This is accessed by TargetNameLoc.
   SourceLocation IdentLoc;
 
   /// The nested-name-specifier that precedes the namespace.
   NestedNameSpecifierLoc QualifierLoc;
 
   /// The Decl that this alias points to, either a NamespaceDecl or
   /// a NamespaceAliasDecl.
   NamedDecl *Namespace;
 
   NamespaceAliasDecl(ASTContext &C, DeclContext *DC,
                      SourceLocation NamespaceLoc, SourceLocation AliasLoc,
                      IdentifierInfo *Alias, NestedNameSpecifierLoc QualifierLoc,
                      SourceLocation IdentLoc, NamedDecl *Namespace)
       : NamedDecl(NamespaceAlias, DC, AliasLoc, Alias), redeclarable_base(C),
         NamespaceLoc(NamespaceLoc), IdentLoc(IdentLoc),
         QualifierLoc(QualifierLoc), Namespace(Namespace) {}
 
   void anchor() override;
 
   using redeclarable_base = Redeclarable<NamespaceAliasDecl>;
 
   NamespaceAliasDecl *getNextRedeclarationImpl() override;
   NamespaceAliasDecl *getPreviousDeclImpl() override;
   NamespaceAliasDecl *getMostRecentDeclImpl() override;
 
 public:
   static NamespaceAliasDecl *Create(ASTContext &C, DeclContext *DC,
                                     SourceLocation NamespaceLoc,
                                     SourceLocation AliasLoc,
                                     IdentifierInfo *Alias,
                                     NestedNameSpecifierLoc QualifierLoc,
                                     SourceLocation IdentLoc,
                                     NamedDecl *Namespace);
 
   static NamespaceAliasDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   using redecl_range = redeclarable_base::redecl_range;
   using redecl_iterator = redeclarable_base::redecl_iterator;
 
   using redeclarable_base::redecls_begin;
   using redeclarable_base::redecls_end;
   using redeclarable_base::redecls;
   using redeclarable_base::getPreviousDecl;
   using redeclarable_base::getMostRecentDecl;
 
   NamespaceAliasDecl *getCanonicalDecl() override {
     return getFirstDecl();
   }
   const NamespaceAliasDecl *getCanonicalDecl() const {
     return getFirstDecl();
   }
 
   /// Retrieve the nested-name-specifier that qualifies the
   /// name of the namespace, with source-location information.
   NestedNameSpecifierLoc getQualifierLoc() const { return QualifierLoc; }
 
   /// Retrieve the nested-name-specifier that qualifies the
   /// name of the namespace.
   NestedNameSpecifier *getQualifier() const {
     return QualifierLoc.getNestedNameSpecifier();
   }
 
   /// Retrieve the namespace declaration aliased by this directive.
   NamespaceDecl *getNamespace() {
     if (auto *AD = dyn_cast<NamespaceAliasDecl>(Namespace))
       return AD->getNamespace();
 
     return cast<NamespaceDecl>(Namespace);
   }
 
   const NamespaceDecl *getNamespace() const {
     return const_cast<NamespaceAliasDecl *>(this)->getNamespace();
   }
 
   /// Returns the location of the alias name, i.e. 'foo' in
   /// "namespace foo = ns::bar;".
   SourceLocation getAliasLoc() const { return getLocation(); }
 
   /// Returns the location of the \c namespace keyword.
   SourceLocation getNamespaceLoc() const { return NamespaceLoc; }
 
   /// Returns the location of the identifier in the named namespace.
   SourceLocation getTargetNameLoc() const { return IdentLoc; }
 
   /// Retrieve the namespace that this alias refers to, which
   /// may either be a NamespaceDecl or a NamespaceAliasDecl.
   NamedDecl *getAliasedNamespace() const { return Namespace; }
 
   SourceRange getSourceRange() const override LLVM_READONLY {
     return SourceRange(NamespaceLoc, IdentLoc);
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == NamespaceAlias; }
 };
 
 /// Implicit declaration of a temporary that was materialized by
 /// a MaterializeTemporaryExpr and lifetime-extended by a declaration
 class LifetimeExtendedTemporaryDecl final
     : public Decl,
       public Mergeable<LifetimeExtendedTemporaryDecl> {
   friend class MaterializeTemporaryExpr;
   friend class ASTDeclReader;
 
   Stmt *ExprWithTemporary = nullptr;
 
   /// The declaration which lifetime-extended this reference, if any.
   /// Either a VarDecl, or (for a ctor-initializer) a FieldDecl.
   ValueDecl *ExtendingDecl = nullptr;
   unsigned ManglingNumber;
 
   mutable APValue *Value = nullptr;
 
   virtual void anchor();
 
   LifetimeExtendedTemporaryDecl(Expr *Temp, ValueDecl *EDecl, unsigned Mangling)
       : Decl(Decl::LifetimeExtendedTemporary, EDecl->getDeclContext(),
              EDecl->getLocation()),
         ExprWithTemporary(Temp), ExtendingDecl(EDecl),
         ManglingNumber(Mangling) {}
 
   LifetimeExtendedTemporaryDecl(EmptyShell)
       : Decl(Decl::LifetimeExtendedTemporary, EmptyShell{}) {}
 
 public:
   static LifetimeExtendedTemporaryDecl *Create(Expr *Temp, ValueDecl *EDec,
                                                unsigned Mangling) {
     return new (EDec->getASTContext(), EDec->getDeclContext())
         LifetimeExtendedTemporaryDecl(Temp, EDec, Mangling);
   }
   static LifetimeExtendedTemporaryDecl *CreateDeserialized(ASTContext &C,
                                                            GlobalDeclID ID) {
     return new (C, ID) LifetimeExtendedTemporaryDecl(EmptyShell{});
   }
 
   ValueDecl *getExtendingDecl() { return ExtendingDecl; }
   const ValueDecl *getExtendingDecl() const { return ExtendingDecl; }
 
   /// Retrieve the storage duration for the materialized temporary.
   StorageDuration getStorageDuration() const;
 
   /// Retrieve the expression to which the temporary materialization conversion
   /// was applied. This isn't necessarily the initializer of the temporary due
   /// to the C++98 delayed materialization rules, but
   /// skipRValueSubobjectAdjustments can be used to find said initializer within
   /// the subexpression.
   Expr *getTemporaryExpr() { return cast<Expr>(ExprWithTemporary); }
   const Expr *getTemporaryExpr() const { return cast<Expr>(ExprWithTemporary); }
 
   unsigned getManglingNumber() const { return ManglingNumber; }
 
   /// Get the storage for the constant value of a materialized temporary
   /// of static storage duration.
   APValue *getOrCreateValue(bool MayCreate) const;
 
   APValue *getValue() const { return Value; }
 
   // Iterators
   Stmt::child_range childrenExpr() {
     return Stmt::child_range(&ExprWithTemporary, &ExprWithTemporary + 1);
   }
 
   Stmt::const_child_range childrenExpr() const {
     return Stmt::const_child_range(&ExprWithTemporary, &ExprWithTemporary + 1);
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) {
     return K == Decl::LifetimeExtendedTemporary;
   }
 };
 
 /// Represents a shadow declaration implicitly introduced into a scope by a
 /// (resolved) using-declaration or using-enum-declaration to achieve
 /// the desired lookup semantics.
 ///
 /// For example:
 /// \code
 /// namespace A {
 ///   void foo();
 ///   void foo(int);
 ///   struct foo {};
 ///   enum bar { bar1, bar2 };
 /// }
 /// namespace B {
 ///   // add a UsingDecl and three UsingShadowDecls (named foo) to B.
 ///   using A::foo;
 ///   // adds UsingEnumDecl and two UsingShadowDecls (named bar1 and bar2) to B.
 ///   using enum A::bar;
 /// }
 /// \endcode
 class UsingShadowDecl : public NamedDecl, public Redeclarable<UsingShadowDecl> {
   friend class BaseUsingDecl;
 
   /// The referenced declaration.
   NamedDecl *Underlying = nullptr;
 
   /// The using declaration which introduced this decl or the next using
   /// shadow declaration contained in the aforementioned using declaration.
   NamedDecl *UsingOrNextShadow = nullptr;
 
   void anchor() override;
 
   using redeclarable_base = Redeclarable<UsingShadowDecl>;
 
   UsingShadowDecl *getNextRedeclarationImpl() override {
     return getNextRedeclaration();
   }
 
   UsingShadowDecl *getPreviousDeclImpl() override {
     return getPreviousDecl();
   }
 
   UsingShadowDecl *getMostRecentDeclImpl() override {
     return getMostRecentDecl();
   }
 
 protected:
   UsingShadowDecl(Kind K, ASTContext &C, DeclContext *DC, SourceLocation Loc,
                   DeclarationName Name, BaseUsingDecl *Introducer,
                   NamedDecl *Target);
   UsingShadowDecl(Kind K, ASTContext &C, EmptyShell);
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   static UsingShadowDecl *Create(ASTContext &C, DeclContext *DC,
                                  SourceLocation Loc, DeclarationName Name,
                                  BaseUsingDecl *Introducer, NamedDecl *Target) {
     return new (C, DC)
         UsingShadowDecl(UsingShadow, C, DC, Loc, Name, Introducer, Target);
   }
 
   static UsingShadowDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   using redecl_range = redeclarable_base::redecl_range;
   using redecl_iterator = redeclarable_base::redecl_iterator;
 
   using redeclarable_base::redecls_begin;
   using redeclarable_base::redecls_end;
   using redeclarable_base::redecls;
   using redeclarable_base::getPreviousDecl;
   using redeclarable_base::getMostRecentDecl;
   using redeclarable_base::isFirstDecl;
 
   UsingShadowDecl *getCanonicalDecl() override {
     return getFirstDecl();
   }
   const UsingShadowDecl *getCanonicalDecl() const {
     return getFirstDecl();
   }
 
   /// Gets the underlying declaration which has been brought into the
   /// local scope.
   NamedDecl *getTargetDecl() const { return Underlying; }
 
   /// Sets the underlying declaration which has been brought into the
   /// local scope.
   void setTargetDecl(NamedDecl *ND) {
     assert(ND && "Target decl is null!");
     Underlying = ND;
     // A UsingShadowDecl is never a friend or local extern declaration, even
     // if it is a shadow declaration for one.
     IdentifierNamespace =
         ND->getIdentifierNamespace() &
         ~(IDNS_OrdinaryFriend | IDNS_TagFriend | IDNS_LocalExtern);
   }
 
   /// Gets the (written or instantiated) using declaration that introduced this
   /// declaration.
   BaseUsingDecl *getIntroducer() const;
 
   /// The next using shadow declaration contained in the shadow decl
   /// chain of the using declaration which introduced this decl.
   UsingShadowDecl *getNextUsingShadowDecl() const {
     return dyn_cast_or_null<UsingShadowDecl>(UsingOrNextShadow);
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) {
     return K == Decl::UsingShadow || K == Decl::ConstructorUsingShadow;
   }
 };
 
 /// Represents a C++ declaration that introduces decls from somewhere else. It
 /// provides a set of the shadow decls so introduced.
 
 class BaseUsingDecl : public NamedDecl {
   /// The first shadow declaration of the shadow decl chain associated
   /// with this using declaration.
   ///
   /// The bool member of the pair is a bool flag a derived type may use
   /// (UsingDecl makes use of it).
   llvm::PointerIntPair<UsingShadowDecl *, 1, bool> FirstUsingShadow;
 
 protected:
   BaseUsingDecl(Kind DK, DeclContext *DC, SourceLocation L, DeclarationName N)
       : NamedDecl(DK, DC, L, N), FirstUsingShadow(nullptr, false) {}
 
 private:
   void anchor() override;
 
 protected:
   /// A bool flag for use by a derived type
   bool getShadowFlag() const { return FirstUsingShadow.getInt(); }
 
   /// A bool flag a derived type may set
   void setShadowFlag(bool V) { FirstUsingShadow.setInt(V); }
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   /// Iterates through the using shadow declarations associated with
   /// this using declaration.
   class shadow_iterator {
     /// The current using shadow declaration.
     UsingShadowDecl *Current = nullptr;
 
   public:
     using value_type = UsingShadowDecl *;
     using reference = UsingShadowDecl *;
     using pointer = UsingShadowDecl *;
     using iterator_category = std::forward_iterator_tag;
     using difference_type = std::ptrdiff_t;
 
     shadow_iterator() = default;
     explicit shadow_iterator(UsingShadowDecl *C) : Current(C) {}
 
     reference operator*() const { return Current; }
     pointer operator->() const { return Current; }
 
     shadow_iterator &operator++() {
       Current = Current->getNextUsingShadowDecl();
       return *this;
     }
 
     shadow_iterator operator++(int) {
       shadow_iterator tmp(*this);
       ++(*this);
       return tmp;
     }
 
     friend bool operator==(shadow_iterator x, shadow_iterator y) {
       return x.Current == y.Current;
     }
     friend bool operator!=(shadow_iterator x, shadow_iterator y) {
       return x.Current != y.Current;
     }
   };
 
   using shadow_range = llvm::iterator_range<shadow_iterator>;
 
   shadow_range shadows() const {
     return shadow_range(shadow_begin(), shadow_end());
   }
 
   shadow_iterator shadow_begin() const {
     return shadow_iterator(FirstUsingShadow.getPointer());
   }
 
   shadow_iterator shadow_end() const { return shadow_iterator(); }
 
   /// Return the number of shadowed declarations associated with this
   /// using declaration.
   unsigned shadow_size() const {
     return std::distance(shadow_begin(), shadow_end());
   }
 
   void addShadowDecl(UsingShadowDecl *S);
   void removeShadowDecl(UsingShadowDecl *S);
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Using || K == UsingEnum; }
 };
 
 /// Represents a C++ using-declaration.
 ///
 /// For example:
 /// \code
 ///    using someNameSpace::someIdentifier;
 /// \endcode
 class UsingDecl : public BaseUsingDecl, public Mergeable<UsingDecl> {
   /// The source location of the 'using' keyword itself.
   SourceLocation UsingLocation;
 
   /// The nested-name-specifier that precedes the name.
   NestedNameSpecifierLoc QualifierLoc;
 
   /// Provides source/type location info for the declaration name
   /// embedded in the ValueDecl base class.
   DeclarationNameLoc DNLoc;
 
   UsingDecl(DeclContext *DC, SourceLocation UL,
             NestedNameSpecifierLoc QualifierLoc,
             const DeclarationNameInfo &NameInfo, bool HasTypenameKeyword)
       : BaseUsingDecl(Using, DC, NameInfo.getLoc(), NameInfo.getName()),
         UsingLocation(UL), QualifierLoc(QualifierLoc),
         DNLoc(NameInfo.getInfo()) {
     setShadowFlag(HasTypenameKeyword);
   }
 
   void anchor() override;
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   /// Return the source location of the 'using' keyword.
   SourceLocation getUsingLoc() const { return UsingLocation; }
 
   /// Set the source location of the 'using' keyword.
   void setUsingLoc(SourceLocation L) { UsingLocation = L; }
 
   /// Retrieve the nested-name-specifier that qualifies the name,
   /// with source-location information.
   NestedNameSpecifierLoc getQualifierLoc() const { return QualifierLoc; }
 
   /// Retrieve the nested-name-specifier that qualifies the name.
   NestedNameSpecifier *getQualifier() const {
     return QualifierLoc.getNestedNameSpecifier();
   }
 
   DeclarationNameInfo getNameInfo() const {
     return DeclarationNameInfo(getDeclName(), getLocation(), DNLoc);
   }
 
   /// Return true if it is a C++03 access declaration (no 'using').
   bool isAccessDeclaration() const { return UsingLocation.isInvalid(); }
 
   /// Return true if the using declaration has 'typename'.
   bool hasTypename() const { return getShadowFlag(); }
 
   /// Sets whether the using declaration has 'typename'.
   void setTypename(bool TN) { setShadowFlag(TN); }
 
   static UsingDecl *Create(ASTContext &C, DeclContext *DC,
                            SourceLocation UsingL,
                            NestedNameSpecifierLoc QualifierLoc,
                            const DeclarationNameInfo &NameInfo,
                            bool HasTypenameKeyword);
 
   static UsingDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   SourceRange getSourceRange() const override LLVM_READONLY;
 
   /// Retrieves the canonical declaration of this declaration.
   UsingDecl *getCanonicalDecl() override {
     return cast<UsingDecl>(getFirstDecl());
   }
   const UsingDecl *getCanonicalDecl() const {
     return cast<UsingDecl>(getFirstDecl());
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Using; }
 };
 
 /// Represents a shadow constructor declaration introduced into a
 /// class by a C++11 using-declaration that names a constructor.
 ///
 /// For example:
 /// \code
 /// struct Base { Base(int); };
 /// struct Derived {
 ///    using Base::Base; // creates a UsingDecl and a ConstructorUsingShadowDecl
 /// };
 /// \endcode
 class ConstructorUsingShadowDecl final : public UsingShadowDecl {
   /// If this constructor using declaration inherted the constructor
   /// from an indirect base class, this is the ConstructorUsingShadowDecl
   /// in the named direct base class from which the declaration was inherited.
   ConstructorUsingShadowDecl *NominatedBaseClassShadowDecl = nullptr;
 
   /// If this constructor using declaration inherted the constructor
   /// from an indirect base class, this is the ConstructorUsingShadowDecl
   /// that will be used to construct the unique direct or virtual base class
   /// that receives the constructor arguments.
   ConstructorUsingShadowDecl *ConstructedBaseClassShadowDecl = nullptr;
 
   /// \c true if the constructor ultimately named by this using shadow
   /// declaration is within a virtual base class subobject of the class that
   /// contains this declaration.
   LLVM_PREFERRED_TYPE(bool)
   unsigned IsVirtual : 1;
 
   ConstructorUsingShadowDecl(ASTContext &C, DeclContext *DC, SourceLocation Loc,
                              UsingDecl *Using, NamedDecl *Target,
                              bool TargetInVirtualBase)
       : UsingShadowDecl(ConstructorUsingShadow, C, DC, Loc,
                         Using->getDeclName(), Using,
                         Target->getUnderlyingDecl()),
         NominatedBaseClassShadowDecl(
             dyn_cast<ConstructorUsingShadowDecl>(Target)),
         ConstructedBaseClassShadowDecl(NominatedBaseClassShadowDecl),
         IsVirtual(TargetInVirtualBase) {
     // If we found a constructor that chains to a constructor for a virtual
     // base, we should directly call that virtual base constructor instead.
     // FIXME: This logic belongs in Sema.
     if (NominatedBaseClassShadowDecl &&
         NominatedBaseClassShadowDecl->constructsVirtualBase()) {
       ConstructedBaseClassShadowDecl =
           NominatedBaseClassShadowDecl->ConstructedBaseClassShadowDecl;
       IsVirtual = true;
     }
   }
 
   ConstructorUsingShadowDecl(ASTContext &C, EmptyShell Empty)
       : UsingShadowDecl(ConstructorUsingShadow, C, Empty), IsVirtual(false) {}
 
   void anchor() override;
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   static ConstructorUsingShadowDecl *Create(ASTContext &C, DeclContext *DC,
                                             SourceLocation Loc,
                                             UsingDecl *Using, NamedDecl *Target,
                                             bool IsVirtual);
   static ConstructorUsingShadowDecl *CreateDeserialized(ASTContext &C,
                                                         GlobalDeclID ID);
 
   /// Override the UsingShadowDecl's getIntroducer, returning the UsingDecl that
   /// introduced this.
   UsingDecl *getIntroducer() const {
     return cast<UsingDecl>(UsingShadowDecl::getIntroducer());
   }
 
   /// Returns the parent of this using shadow declaration, which
   /// is the class in which this is declared.
   //@{
   const CXXRecordDecl *getParent() const {
     return cast<CXXRecordDecl>(getDeclContext());
   }
   CXXRecordDecl *getParent() {
     return cast<CXXRecordDecl>(getDeclContext());
   }
   //@}
 
   /// Get the inheriting constructor declaration for the direct base
   /// class from which this using shadow declaration was inherited, if there is
   /// one. This can be different for each redeclaration of the same shadow decl.
   ConstructorUsingShadowDecl *getNominatedBaseClassShadowDecl() const {
     return NominatedBaseClassShadowDecl;
   }
 
   /// Get the inheriting constructor declaration for the base class
   /// for which we don't have an explicit initializer, if there is one.
   ConstructorUsingShadowDecl *getConstructedBaseClassShadowDecl() const {
     return ConstructedBaseClassShadowDecl;
   }
 
   /// Get the base class that was named in the using declaration. This
   /// can be different for each redeclaration of this same shadow decl.
   CXXRecordDecl *getNominatedBaseClass() const;
 
   /// Get the base class whose constructor or constructor shadow
   /// declaration is passed the constructor arguments.
   CXXRecordDecl *getConstructedBaseClass() const {
     return cast<CXXRecordDecl>((ConstructedBaseClassShadowDecl
                                     ? ConstructedBaseClassShadowDecl
                                     : getTargetDecl())
                                    ->getDeclContext());
   }
 
   /// Returns \c true if the constructed base class is a virtual base
   /// class subobject of this declaration's class.
   bool constructsVirtualBase() const {
     return IsVirtual;
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == ConstructorUsingShadow; }
 };
 
 /// Represents a C++ using-enum-declaration.
 ///
 /// For example:
 /// \code
 ///    using enum SomeEnumTag ;
 /// \endcode
 
 class UsingEnumDecl : public BaseUsingDecl, public Mergeable<UsingEnumDecl> {
   /// The source location of the 'using' keyword itself.
   SourceLocation UsingLocation;
   /// The source location of the 'enum' keyword.
   SourceLocation EnumLocation;
   /// 'qual::SomeEnum' as an EnumType, possibly with Elaborated/Typedef sugar.
   TypeSourceInfo *EnumType;
 
   UsingEnumDecl(DeclContext *DC, DeclarationName DN, SourceLocation UL,
                 SourceLocation EL, SourceLocation NL, TypeSourceInfo *EnumType)
       : BaseUsingDecl(UsingEnum, DC, NL, DN), UsingLocation(UL), EnumLocation(EL),
         EnumType(EnumType){}
 
   void anchor() override;
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   /// The source location of the 'using' keyword.
   SourceLocation getUsingLoc() const { return UsingLocation; }
   void setUsingLoc(SourceLocation L) { UsingLocation = L; }
 
   /// The source location of the 'enum' keyword.
   SourceLocation getEnumLoc() const { return EnumLocation; }
   void setEnumLoc(SourceLocation L) { EnumLocation = L; }
   NestedNameSpecifier *getQualifier() const {
     return getQualifierLoc().getNestedNameSpecifier();
   }
   NestedNameSpecifierLoc getQualifierLoc() const {
     if (auto ETL = EnumType->getTypeLoc().getAs<ElaboratedTypeLoc>())
       return ETL.getQualifierLoc();
     return NestedNameSpecifierLoc();
   }
   // Returns the "qualifier::Name" part as a TypeLoc.
   TypeLoc getEnumTypeLoc() const {
     return EnumType->getTypeLoc();
   }
   TypeSourceInfo *getEnumType() const {
     return EnumType;
   }
   void setEnumType(TypeSourceInfo *TSI) { EnumType = TSI; }
 
 public:
   EnumDecl *getEnumDecl() const { return cast<EnumDecl>(EnumType->getType()->getAsTagDecl()); }
 
   static UsingEnumDecl *Create(ASTContext &C, DeclContext *DC,
                                SourceLocation UsingL, SourceLocation EnumL,
                                SourceLocation NameL, TypeSourceInfo *EnumType);
 
   static UsingEnumDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   SourceRange getSourceRange() const override LLVM_READONLY;
 
   /// Retrieves the canonical declaration of this declaration.
   UsingEnumDecl *getCanonicalDecl() override {
     return cast<UsingEnumDecl>(getFirstDecl());
   }
   const UsingEnumDecl *getCanonicalDecl() const {
     return cast<UsingEnumDecl>(getFirstDecl());
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == UsingEnum; }
 };
 
 /// Represents a pack of using declarations that a single
 /// using-declarator pack-expanded into.
 ///
 /// \code
 /// template<typename ...T> struct X : T... {
 ///   using T::operator()...;
 ///   using T::operator T...;
 /// };
 /// \endcode
 ///
 /// In the second case above, the UsingPackDecl will have the name
 /// 'operator T' (which contains an unexpanded pack), but the individual
 /// UsingDecls and UsingShadowDecls will have more reasonable names.
 class UsingPackDecl final
     : public NamedDecl, public Mergeable<UsingPackDecl>,
       private llvm::TrailingObjects<UsingPackDecl, NamedDecl *> {
   /// The UnresolvedUsingValueDecl or UnresolvedUsingTypenameDecl from
   /// which this waas instantiated.
   NamedDecl *InstantiatedFrom;
 
   /// The number of using-declarations created by this pack expansion.
   unsigned NumExpansions;
 
   UsingPackDecl(DeclContext *DC, NamedDecl *InstantiatedFrom,
                 ArrayRef<NamedDecl *> UsingDecls)
       : NamedDecl(UsingPack, DC,
                   InstantiatedFrom ? InstantiatedFrom->getLocation()
                                    : SourceLocation(),
                   InstantiatedFrom ? InstantiatedFrom->getDeclName()
                                    : DeclarationName()),
         InstantiatedFrom(InstantiatedFrom), NumExpansions(UsingDecls.size()) {
     std::uninitialized_copy(UsingDecls.begin(), UsingDecls.end(),
                             getTrailingObjects<NamedDecl *>());
   }
 
   void anchor() override;
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
   friend TrailingObjects;
 
   /// Get the using declaration from which this was instantiated. This will
   /// always be an UnresolvedUsingValueDecl or an UnresolvedUsingTypenameDecl
   /// that is a pack expansion.
   NamedDecl *getInstantiatedFromUsingDecl() const { return InstantiatedFrom; }
 
   /// Get the set of using declarations that this pack expanded into. Note that
   /// some of these may still be unresolved.
   ArrayRef<NamedDecl *> expansions() const {
     return llvm::ArrayRef(getTrailingObjects<NamedDecl *>(), NumExpansions);
   }
 
   static UsingPackDecl *Create(ASTContext &C, DeclContext *DC,
                                NamedDecl *InstantiatedFrom,
                                ArrayRef<NamedDecl *> UsingDecls);
 
   static UsingPackDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID,
                                            unsigned NumExpansions);
 
   SourceRange getSourceRange() const override LLVM_READONLY {
     return InstantiatedFrom->getSourceRange();
   }
 
   UsingPackDecl *getCanonicalDecl() override { return getFirstDecl(); }
   const UsingPackDecl *getCanonicalDecl() const { return getFirstDecl(); }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == UsingPack; }
 };
 
 /// Represents a dependent using declaration which was not marked with
 /// \c typename.
 ///
 /// Unlike non-dependent using declarations, these *only* bring through
 /// non-types; otherwise they would break two-phase lookup.
 ///
 /// \code
 /// template \<class T> class A : public Base<T> {
 ///   using Base<T>::foo;
 /// };
 /// \endcode
 class UnresolvedUsingValueDecl : public ValueDecl,
                                  public Mergeable<UnresolvedUsingValueDecl> {
   /// The source location of the 'using' keyword
   SourceLocation UsingLocation;
 
   /// If this is a pack expansion, the location of the '...'.
   SourceLocation EllipsisLoc;
 
   /// The nested-name-specifier that precedes the name.
   NestedNameSpecifierLoc QualifierLoc;
 
   /// Provides source/type location info for the declaration name
   /// embedded in the ValueDecl base class.
   DeclarationNameLoc DNLoc;
 
   UnresolvedUsingValueDecl(DeclContext *DC, QualType Ty,
                            SourceLocation UsingLoc,
                            NestedNameSpecifierLoc QualifierLoc,
                            const DeclarationNameInfo &NameInfo,
                            SourceLocation EllipsisLoc)
       : ValueDecl(UnresolvedUsingValue, DC,
                   NameInfo.getLoc(), NameInfo.getName(), Ty),
         UsingLocation(UsingLoc), EllipsisLoc(EllipsisLoc),
         QualifierLoc(QualifierLoc), DNLoc(NameInfo.getInfo()) {}
 
   void anchor() override;
 
 public:
   friend class ASTDeclReader;
   friend class ASTDeclWriter;
 
   /// Returns the source location of the 'using' keyword.
   SourceLocation getUsingLoc() const { return UsingLocation; }
 
   /// Set the source location of the 'using' keyword.
   void setUsingLoc(SourceLocation L) { UsingLocation = L; }
 
   /// Return true if it is a C++03 access declaration (no 'using').
   bool isAccessDeclaration() const { return UsingLocation.isInvalid(); }
 
   /// Retrieve the nested-name-specifier that qualifies the name,
   /// with source-location information.
   NestedNameSpecifierLoc getQualifierLoc() const { return QualifierLoc; }
 
   /// Retrieve the nested-name-specifier that qualifies the name.
   NestedNameSpecifier *getQualifier() const {
     return QualifierLoc.getNestedNameSpecifier();
   }
 
   DeclarationNameInfo getNameInfo() const {
     return DeclarationNameInfo(getDeclName(), getLocation(), DNLoc);
   }
 
   /// Determine whether this is a pack expansion.
   bool isPackExpansion() const {
     return EllipsisLoc.isValid();
   }
 
   /// Get the location of the ellipsis if this is a pack expansion.
   SourceLocation getEllipsisLoc() const {
     return EllipsisLoc;
   }
 
   static UnresolvedUsingValueDecl *
     Create(ASTContext &C, DeclContext *DC, SourceLocation UsingLoc,
            NestedNameSpecifierLoc QualifierLoc,
            const DeclarationNameInfo &NameInfo, SourceLocation EllipsisLoc);
 
   static UnresolvedUsingValueDecl *CreateDeserialized(ASTContext &C,
                                                       GlobalDeclID ID);
 
   SourceRange getSourceRange() const override LLVM_READONLY;
 
   /// Retrieves the canonical declaration of this declaration.
   UnresolvedUsingValueDecl *getCanonicalDecl() override {
     return getFirstDecl();
   }
   const UnresolvedUsingValueDecl *getCanonicalDecl() const {
     return getFirstDecl();
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == UnresolvedUsingValue; }
 };
 
 /// Represents a dependent using declaration which was marked with
 /// \c typename.
 ///
 /// \code
 /// template \<class T> class A : public Base<T> {
 ///   using typename Base<T>::foo;
 /// };
 /// \endcode
 ///
 /// The type associated with an unresolved using typename decl is
 /// currently always a typename type.
 class UnresolvedUsingTypenameDecl
     : public TypeDecl,
       public Mergeable<UnresolvedUsingTypenameDecl> {
   friend class ASTDeclReader;
 
   /// The source location of the 'typename' keyword
   SourceLocation TypenameLocation;
 
   /// If this is a pack expansion, the location of the '...'.
   SourceLocation EllipsisLoc;
 
   /// The nested-name-specifier that precedes the name.
   NestedNameSpecifierLoc QualifierLoc;
 
   UnresolvedUsingTypenameDecl(DeclContext *DC, SourceLocation UsingLoc,
                               SourceLocation TypenameLoc,
                               NestedNameSpecifierLoc QualifierLoc,
                               SourceLocation TargetNameLoc,
                               IdentifierInfo *TargetName,
                               SourceLocation EllipsisLoc)
     : TypeDecl(UnresolvedUsingTypename, DC, TargetNameLoc, TargetName,
                UsingLoc),
       TypenameLocation(TypenameLoc), EllipsisLoc(EllipsisLoc),
       QualifierLoc(QualifierLoc) {}
 
   void anchor() override;
 
 public:
   /// Returns the source location of the 'using' keyword.
   SourceLocation getUsingLoc() const { return getBeginLoc(); }
 
   /// Returns the source location of the 'typename' keyword.
   SourceLocation getTypenameLoc() const { return TypenameLocation; }
 
   /// Retrieve the nested-name-specifier that qualifies the name,
   /// with source-location information.
   NestedNameSpecifierLoc getQualifierLoc() const { return QualifierLoc; }
 
   /// Retrieve the nested-name-specifier that qualifies the name.
   NestedNameSpecifier *getQualifier() const {
     return QualifierLoc.getNestedNameSpecifier();
   }
 
   DeclarationNameInfo getNameInfo() const {
     return DeclarationNameInfo(getDeclName(), getLocation());
   }
 
   /// Determine whether this is a pack expansion.
   bool isPackExpansion() const {
     return EllipsisLoc.isValid();
   }
 
   /// Get the location of the ellipsis if this is a pack expansion.
   SourceLocation getEllipsisLoc() const {
     return EllipsisLoc;
   }
 
   static UnresolvedUsingTypenameDecl *
     Create(ASTContext &C, DeclContext *DC, SourceLocation UsingLoc,
            SourceLocation TypenameLoc, NestedNameSpecifierLoc QualifierLoc,
            SourceLocation TargetNameLoc, DeclarationName TargetName,
            SourceLocation EllipsisLoc);
 
   static UnresolvedUsingTypenameDecl *CreateDeserialized(ASTContext &C,
                                                          GlobalDeclID ID);
 
   /// Retrieves the canonical declaration of this declaration.
   UnresolvedUsingTypenameDecl *getCanonicalDecl() override {
     return getFirstDecl();
   }
   const UnresolvedUsingTypenameDecl *getCanonicalDecl() const {
     return getFirstDecl();
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == UnresolvedUsingTypename; }
 };
 
 /// This node is generated when a using-declaration that was annotated with
 /// __attribute__((using_if_exists)) failed to resolve to a known declaration.
 /// In that case, Sema builds a UsingShadowDecl whose target is an instance of
 /// this declaration, adding it to the current scope. Referring to this
 /// declaration in any way is an error.
 class UnresolvedUsingIfExistsDecl final : public NamedDecl {
   UnresolvedUsingIfExistsDecl(DeclContext *DC, SourceLocation Loc,
                               DeclarationName Name);
 
   void anchor() override;
 
 public:
   static UnresolvedUsingIfExistsDecl *Create(ASTContext &Ctx, DeclContext *DC,
                                              SourceLocation Loc,
                                              DeclarationName Name);
   static UnresolvedUsingIfExistsDecl *CreateDeserialized(ASTContext &Ctx,
                                                          GlobalDeclID ID);
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Decl::UnresolvedUsingIfExists; }
 };
 
 /// Represents a C++11 static_assert declaration.
 class StaticAssertDecl : public Decl {
   llvm::PointerIntPair<Expr *, 1, bool> AssertExprAndFailed;
   Expr *Message;
   SourceLocation RParenLoc;
 
   StaticAssertDecl(DeclContext *DC, SourceLocation StaticAssertLoc,
                    Expr *AssertExpr, Expr *Message, SourceLocation RParenLoc,
                    bool Failed)
       : Decl(StaticAssert, DC, StaticAssertLoc),
         AssertExprAndFailed(AssertExpr, Failed), Message(Message),
         RParenLoc(RParenLoc) {}
 
   virtual void anchor();
 
 public:
   friend class ASTDeclReader;
 
   static StaticAssertDecl *Create(ASTContext &C, DeclContext *DC,
                                   SourceLocation StaticAssertLoc,
                                   Expr *AssertExpr, Expr *Message,
                                   SourceLocation RParenLoc, bool Failed);
   static StaticAssertDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   Expr *getAssertExpr() { return AssertExprAndFailed.getPointer(); }
   const Expr *getAssertExpr() const { return AssertExprAndFailed.getPointer(); }
 
   Expr *getMessage() { return Message; }
   const Expr *getMessage() const { return Message; }
 
   bool isFailed() const { return AssertExprAndFailed.getInt(); }
 
   SourceLocation getRParenLoc() const { return RParenLoc; }
 
   SourceRange getSourceRange() const override LLVM_READONLY {
     return SourceRange(getLocation(), getRParenLoc());
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == StaticAssert; }
 };
 
 /// A binding in a decomposition declaration. For instance, given:
 ///
 ///   int n[3];
 ///   auto &[a, b, c] = n;
 ///
 /// a, b, and c are BindingDecls, whose bindings are the expressions
 /// x[0], x[1], and x[2] respectively, where x is the implicit
 /// DecompositionDecl of type 'int (&)[3]'.
 class BindingDecl : public ValueDecl {
   /// The declaration that this binding binds to part of.
   ValueDecl *Decomp;
   /// The binding represented by this declaration. References to this
   /// declaration are effectively equivalent to this expression (except
   /// that it is only evaluated once at the point of declaration of the
   /// binding).
   Expr *Binding = nullptr;
 
   BindingDecl(DeclContext *DC, SourceLocation IdLoc, IdentifierInfo *Id)
       : ValueDecl(Decl::Binding, DC, IdLoc, Id, QualType()) {}
 
   void anchor() override;
 
 public:
   friend class ASTDeclReader;
 
   static BindingDecl *Create(ASTContext &C, DeclContext *DC,
                              SourceLocation IdLoc, IdentifierInfo *Id);
   static BindingDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   /// Get the expression to which this declaration is bound. This may be null
   /// in two different cases: while parsing the initializer for the
   /// decomposition declaration, and when the initializer is type-dependent.
   Expr *getBinding() const { return Binding; }
 
   /// Get the decomposition declaration that this binding represents a
   /// decomposition of.
   ValueDecl *getDecomposedDecl() const { return Decomp; }
 
   /// Get the variable (if any) that holds the value of evaluating the binding.
   /// Only present for user-defined bindings for tuple-like types.
   VarDecl *getHoldingVar() const;
 
   /// Set the binding for this BindingDecl, along with its declared type (which
   /// should be a possibly-cv-qualified form of the type of the binding, or a
   /// reference to such a type).
   void setBinding(QualType DeclaredType, Expr *Binding) {
     setType(DeclaredType);
     this->Binding = Binding;
   }
 
   /// Set the decomposed variable for this BindingDecl.
   void setDecomposedDecl(ValueDecl *Decomposed) { Decomp = Decomposed; }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Decl::Binding; }
 };
 
 /// A decomposition declaration. For instance, given:
 ///
 ///   int n[3];
 ///   auto &[a, b, c] = n;
 ///
 /// the second line declares a DecompositionDecl of type 'int (&)[3]', and
 /// three BindingDecls (named a, b, and c). An instance of this class is always
 /// unnamed, but behaves in almost all other respects like a VarDecl.
 class DecompositionDecl final
     : public VarDecl,
       private llvm::TrailingObjects<DecompositionDecl, BindingDecl *> {
   /// The number of BindingDecl*s following this object.
   unsigned NumBindings;
 
   DecompositionDecl(ASTContext &C, DeclContext *DC, SourceLocation StartLoc,
                     SourceLocation LSquareLoc, QualType T,
                     TypeSourceInfo *TInfo, StorageClass SC,
                     ArrayRef<BindingDecl *> Bindings)
       : VarDecl(Decomposition, C, DC, StartLoc, LSquareLoc, nullptr, T, TInfo,
                 SC),
         NumBindings(Bindings.size()) {
     std::uninitialized_copy(Bindings.begin(), Bindings.end(),
                             getTrailingObjects<BindingDecl *>());
     for (auto *B : Bindings)
       B->setDecomposedDecl(this);
   }
 
   void anchor() override;
 
 public:
   friend class ASTDeclReader;
   friend TrailingObjects;
 
   static DecompositionDecl *Create(ASTContext &C, DeclContext *DC,
                                    SourceLocation StartLoc,
                                    SourceLocation LSquareLoc,
                                    QualType T, TypeSourceInfo *TInfo,
                                    StorageClass S,
                                    ArrayRef<BindingDecl *> Bindings);
   static DecompositionDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID,
                                                unsigned NumBindings);
 
   ArrayRef<BindingDecl *> bindings() const {
     return llvm::ArrayRef(getTrailingObjects<BindingDecl *>(), NumBindings);
   }
 
   void printName(raw_ostream &OS, const PrintingPolicy &Policy) const override;
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Decomposition; }
 };
 
 /// An instance of this class represents the declaration of a property
 /// member.  This is a Microsoft extension to C++, first introduced in
 /// Visual Studio .NET 2003 as a parallel to similar features in C#
 /// and Managed C++.
 ///
 /// A property must always be a non-static class member.
 ///
 /// A property member superficially resembles a non-static data
 /// member, except preceded by a property attribute:
 ///   __declspec(property(get=GetX, put=PutX)) int x;
 /// Either (but not both) of the 'get' and 'put' names may be omitted.
 ///
 /// A reference to a property is always an lvalue.  If the lvalue
 /// undergoes lvalue-to-rvalue conversion, then a getter name is
 /// required, and that member is called with no arguments.
 /// If the lvalue is assigned into, then a setter name is required,
 /// and that member is called with one argument, the value assigned.
 /// Both operations are potentially overloaded.  Compound assignments
 /// are permitted, as are the increment and decrement operators.
 ///
 /// The getter and putter methods are permitted to be overloaded,
 /// although their return and parameter types are subject to certain
 /// restrictions according to the type of the property.
 ///
 /// A property declared using an incomplete array type may
 /// additionally be subscripted, adding extra parameters to the getter
 /// and putter methods.
 class MSPropertyDecl : public DeclaratorDecl {
   IdentifierInfo *GetterId, *SetterId;
 
   MSPropertyDecl(DeclContext *DC, SourceLocation L, DeclarationName N,
                  QualType T, TypeSourceInfo *TInfo, SourceLocation StartL,
                  IdentifierInfo *Getter, IdentifierInfo *Setter)
       : DeclaratorDecl(MSProperty, DC, L, N, T, TInfo, StartL),
         GetterId(Getter), SetterId(Setter) {}
 
   void anchor() override;
 public:
   friend class ASTDeclReader;
 
   static MSPropertyDecl *Create(ASTContext &C, DeclContext *DC,
                                 SourceLocation L, DeclarationName N, QualType T,
                                 TypeSourceInfo *TInfo, SourceLocation StartL,
                                 IdentifierInfo *Getter, IdentifierInfo *Setter);
   static MSPropertyDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   static bool classof(const Decl *D) { return D->getKind() == MSProperty; }
 
   bool hasGetter() const { return GetterId != nullptr; }
   IdentifierInfo* getGetterId() const { return GetterId; }
   bool hasSetter() const { return SetterId != nullptr; }
   IdentifierInfo* getSetterId() const { return SetterId; }
 };
 
 /// Parts of a decomposed MSGuidDecl. Factored out to avoid unnecessary
 /// dependencies on DeclCXX.h.
 struct MSGuidDeclParts {
   /// {01234567-...
   uint32_t Part1;
   /// ...-89ab-...
   uint16_t Part2;
   /// ...-cdef-...
   uint16_t Part3;
   /// ...-0123-456789abcdef}
   uint8_t Part4And5[8];
 
   uint64_t getPart4And5AsUint64() const {
     uint64_t Val;
     memcpy(&Val, &Part4And5, sizeof(Part4And5));
     return Val;
   }
 };
 
 /// A global _GUID constant. These are implicitly created by UuidAttrs.
 ///
 ///   struct _declspec(uuid("01234567-89ab-cdef-0123-456789abcdef")) X{};
 ///
 /// X is a CXXRecordDecl that contains a UuidAttr that references the (unique)
 /// MSGuidDecl for the specified UUID.
 class MSGuidDecl : public ValueDecl,
                    public Mergeable<MSGuidDecl>,
                    public llvm::FoldingSetNode {
 public:
   using Parts = MSGuidDeclParts;
 
 private:
   /// The decomposed form of the UUID.
   Parts PartVal;
 
   /// The resolved value of the UUID as an APValue. Computed on demand and
   /// cached.
   mutable APValue APVal;
 
   void anchor() override;
 
   MSGuidDecl(DeclContext *DC, QualType T, Parts P);
 
   static MSGuidDecl *Create(const ASTContext &C, QualType T, Parts P);
   static MSGuidDecl *CreateDeserialized(ASTContext &C, GlobalDeclID ID);
 
   // Only ASTContext::getMSGuidDecl and deserialization create these.
   friend class ASTContext;
   friend class ASTReader;
   friend class ASTDeclReader;
 
 public:
   /// Print this UUID in a human-readable format.
   void printName(llvm::raw_ostream &OS,
                  const PrintingPolicy &Policy) const override;
 
   /// Get the decomposed parts of this declaration.
   Parts getParts() const { return PartVal; }
 
   /// Get the value of this MSGuidDecl as an APValue. This may fail and return
   /// an absent APValue if the type of the declaration is not of the expected
   /// shape.
   APValue &getAsAPValue() const;
 
   static void Profile(llvm::FoldingSetNodeID &ID, Parts P) {
     ID.AddInteger(P.Part1);
     ID.AddInteger(P.Part2);
     ID.AddInteger(P.Part3);
     ID.AddInteger(P.getPart4And5AsUint64());
   }
   void Profile(llvm::FoldingSetNodeID &ID) { Profile(ID, PartVal); }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Decl::MSGuid; }
 };
 
 /// An artificial decl, representing a global anonymous constant value which is
 /// uniquified by value within a translation unit.
 ///
 /// These is currently only used to back the LValue returned by
 /// __builtin_source_location, but could potentially be used for other similar
 /// situations in the future.
 class UnnamedGlobalConstantDecl : public ValueDecl,
                                   public Mergeable<UnnamedGlobalConstantDecl>,
                                   public llvm::FoldingSetNode {
 
   // The constant value of this global.
   APValue Value;
 
   void anchor() override;
 
   UnnamedGlobalConstantDecl(const ASTContext &C, DeclContext *DC, QualType T,
                             const APValue &Val);
 
   static UnnamedGlobalConstantDecl *Create(const ASTContext &C, QualType T,
                                            const APValue &APVal);
   static UnnamedGlobalConstantDecl *CreateDeserialized(ASTContext &C,
                                                        GlobalDeclID ID);
 
   // Only ASTContext::getUnnamedGlobalConstantDecl and deserialization create
   // these.
   friend class ASTContext;
   friend class ASTReader;
   friend class ASTDeclReader;
 
 public:
   /// Print this in a human-readable format.
   void printName(llvm::raw_ostream &OS,
                  const PrintingPolicy &Policy) const override;
 
   const APValue &getValue() const { return Value; }
 
   static void Profile(llvm::FoldingSetNodeID &ID, QualType Ty,
                       const APValue &APVal) {
     Ty.Profile(ID);
     APVal.Profile(ID);
   }
   void Profile(llvm::FoldingSetNodeID &ID) {
     Profile(ID, getType(), getValue());
   }
 
   static bool classof(const Decl *D) { return classofKind(D->getKind()); }
   static bool classofKind(Kind K) { return K == Decl::UnnamedGlobalConstant; }
 };
 
 /// Insertion operator for diagnostics.  This allows sending an AccessSpecifier
 /// into a diagnostic with <<.
 const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
                                       AccessSpecifier AS);
 
 } // namespace clang
 
 #endif // LLVM_CLANG_AST_DECLCXX_H