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 //===- TemplateName.h - C++ Template Name Representation --------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 //  This file defines the TemplateName interface and subclasses.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_CLANG_AST_TEMPLATENAME_H
 #define LLVM_CLANG_AST_TEMPLATENAME_H
 
 #include "clang/AST/DependenceFlags.h"
 #include "clang/AST/NestedNameSpecifier.h"
 #include "clang/Basic/LLVM.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/PointerUnion.h"
 #include "llvm/Support/PointerLikeTypeTraits.h"
 #include <cassert>
 #include <optional>
 
 namespace clang {
 
 class ASTContext;
 class Decl;
 class DependentTemplateName;
 class IdentifierInfo;
 class NamedDecl;
 class NestedNameSpecifier;
 enum OverloadedOperatorKind : int;
 class OverloadedTemplateStorage;
 class AssumedTemplateStorage;
 class DeducedTemplateStorage;
 struct PrintingPolicy;
 class QualifiedTemplateName;
 class SubstTemplateTemplateParmPackStorage;
 class SubstTemplateTemplateParmStorage;
 class TemplateArgument;
 class TemplateDecl;
 class TemplateTemplateParmDecl;
 class UsingShadowDecl;
 
 /// Implementation class used to describe either a set of overloaded
 /// template names or an already-substituted template template parameter pack.
 class UncommonTemplateNameStorage {
 protected:
   enum Kind {
     Overloaded,
     Assumed, // defined in DeclarationName.h
     Deduced,
     SubstTemplateTemplateParm,
     SubstTemplateTemplateParmPack
   };
 
   struct BitsTag {
     LLVM_PREFERRED_TYPE(Kind)
     unsigned Kind : 3;
 
     // The template parameter index.
     unsigned Index : 14;
 
     /// The pack index, or the number of stored templates
     /// or template arguments, depending on which subclass we have.
     unsigned Data : 15;
   };
 
   union {
     struct BitsTag Bits;
     void *PointerAlignment;
   };
 
   UncommonTemplateNameStorage(Kind Kind, unsigned Index, unsigned Data) {
     Bits.Kind = Kind;
     Bits.Index = Index;
     Bits.Data = Data;
   }
 
 public:
   OverloadedTemplateStorage *getAsOverloadedStorage()  {
     return Bits.Kind == Overloaded
              ? reinterpret_cast<OverloadedTemplateStorage *>(this)
              : nullptr;
   }
 
   AssumedTemplateStorage *getAsAssumedTemplateName()  {
     return Bits.Kind == Assumed
              ? reinterpret_cast<AssumedTemplateStorage *>(this)
              : nullptr;
   }
 
   DeducedTemplateStorage *getAsDeducedTemplateName() {
     return Bits.Kind == Deduced
                ? reinterpret_cast<DeducedTemplateStorage *>(this)
                : nullptr;
   }
 
   SubstTemplateTemplateParmStorage *getAsSubstTemplateTemplateParm() {
     return Bits.Kind == SubstTemplateTemplateParm
              ? reinterpret_cast<SubstTemplateTemplateParmStorage *>(this)
              : nullptr;
   }
 
   SubstTemplateTemplateParmPackStorage *getAsSubstTemplateTemplateParmPack() {
     return Bits.Kind == SubstTemplateTemplateParmPack
              ? reinterpret_cast<SubstTemplateTemplateParmPackStorage *>(this)
              : nullptr;
   }
 };
 
 /// A structure for storing the information associated with an
 /// overloaded template name.
 class OverloadedTemplateStorage : public UncommonTemplateNameStorage {
   friend class ASTContext;
 
   OverloadedTemplateStorage(unsigned size)
       : UncommonTemplateNameStorage(Overloaded, 0, size) {}
 
   NamedDecl **getStorage() {
     return reinterpret_cast<NamedDecl **>(this + 1);
   }
   NamedDecl * const *getStorage() const {
     return reinterpret_cast<NamedDecl *const *>(this + 1);
   }
 
 public:
   unsigned size() const { return Bits.Data; }
 
   using iterator = NamedDecl *const *;
 
   iterator begin() const { return getStorage(); }
   iterator end() const { return getStorage() + Bits.Data; }
 
   llvm::ArrayRef<NamedDecl*> decls() const {
     return llvm::ArrayRef(begin(), end());
   }
 };
 
 /// A structure for storing an already-substituted template template
 /// parameter pack.
 ///
 /// This kind of template names occurs when the parameter pack has been
 /// provided with a template template argument pack in a context where its
 /// enclosing pack expansion could not be fully expanded.
 class SubstTemplateTemplateParmPackStorage : public UncommonTemplateNameStorage,
                                              public llvm::FoldingSetNode {
   const TemplateArgument *Arguments;
   llvm::PointerIntPair<Decl *, 1, bool> AssociatedDeclAndFinal;
 
 public:
   SubstTemplateTemplateParmPackStorage(ArrayRef<TemplateArgument> ArgPack,
                                        Decl *AssociatedDecl, unsigned Index,
                                        bool Final);
 
   /// A template-like entity which owns the whole pattern being substituted.
   /// This will own a set of template parameters.
   Decl *getAssociatedDecl() const;
 
   /// Returns the index of the replaced parameter in the associated declaration.
   /// This should match the result of `getParameterPack()->getIndex()`.
   unsigned getIndex() const { return Bits.Index; }
 
   // When true the substitution will be 'Final' (subst node won't be placed).
   bool getFinal() const;
 
   /// Retrieve the template template parameter pack being substituted.
   TemplateTemplateParmDecl *getParameterPack() const;
 
   /// Retrieve the template template argument pack with which this
   /// parameter was substituted.
   TemplateArgument getArgumentPack() const;
 
   void Profile(llvm::FoldingSetNodeID &ID, ASTContext &Context);
 
   static void Profile(llvm::FoldingSetNodeID &ID, ASTContext &Context,
                       const TemplateArgument &ArgPack, Decl *AssociatedDecl,
                       unsigned Index, bool Final);
 };
 
 struct DefaultArguments {
   // The position in the template parameter list
   // the first argument corresponds to.
   unsigned StartPos;
   ArrayRef<TemplateArgument> Args;
 
   operator bool() const { return !Args.empty(); }
 };
 
 /// Represents a C++ template name within the type system.
 ///
 /// A C++ template name refers to a template within the C++ type
 /// system. In most cases, a template name is simply a reference to a
 /// class template, e.g.
 ///
 /// \code
 /// template<typename T> class X { };
 ///
 /// X<int> xi;
 /// \endcode
 ///
 /// Here, the 'X' in \c X<int> is a template name that refers to the
 /// declaration of the class template X, above. Template names can
 /// also refer to function templates, C++0x template aliases, etc.
 ///
 /// Some template names are dependent. For example, consider:
 ///
 /// \code
 /// template<typename MetaFun, typename T1, typename T2> struct apply2 {
 ///   typedef typename MetaFun::template apply<T1, T2>::type type;
 /// };
 /// \endcode
 ///
 /// Here, "apply" is treated as a template name within the typename
 /// specifier in the typedef. "apply" is a nested template, and can
 /// only be understood in the context of a template instantiation,
 /// hence is represented as a dependent template name.
 class TemplateName {
   // NameDecl is either a TemplateDecl or a UsingShadowDecl depending on the
   // NameKind.
   // !! There is no free low bits in 32-bit builds to discriminate more than 4
   // pointer types in PointerUnion.
   using StorageType =
       llvm::PointerUnion<Decl *, UncommonTemplateNameStorage *,
                          QualifiedTemplateName *, DependentTemplateName *>;
 
   StorageType Storage;
 
   explicit TemplateName(void *Ptr);
 
 public:
   // Kind of name that is actually stored.
   enum NameKind {
     /// A single template declaration.
     Template,
 
     /// A set of overloaded template declarations.
     OverloadedTemplate,
 
     /// An unqualified-id that has been assumed to name a function template
     /// that will be found by ADL.
     AssumedTemplate,
 
     /// A qualified template name, where the qualification is kept
     /// to describe the source code as written.
     QualifiedTemplate,
 
     /// A dependent template name that has not been resolved to a
     /// template (or set of templates).
     DependentTemplate,
 
     /// A template template parameter that has been substituted
     /// for some other template name.
     SubstTemplateTemplateParm,
 
     /// A template template parameter pack that has been substituted for
     /// a template template argument pack, but has not yet been expanded into
     /// individual arguments.
     SubstTemplateTemplateParmPack,
 
     /// A template name that refers to a template declaration found through a
     /// specific using shadow declaration.
     UsingTemplate,
 
     /// A template name that refers to another TemplateName with deduced default
     /// arguments.
     DeducedTemplate,
   };
 
   TemplateName() = default;
   explicit TemplateName(TemplateDecl *Template);
   explicit TemplateName(OverloadedTemplateStorage *Storage);
   explicit TemplateName(AssumedTemplateStorage *Storage);
   explicit TemplateName(SubstTemplateTemplateParmStorage *Storage);
   explicit TemplateName(SubstTemplateTemplateParmPackStorage *Storage);
   explicit TemplateName(QualifiedTemplateName *Qual);
   explicit TemplateName(DependentTemplateName *Dep);
   explicit TemplateName(UsingShadowDecl *Using);
   explicit TemplateName(DeducedTemplateStorage *Deduced);
 
   /// Determine whether this template name is NULL.
   bool isNull() const;
 
   // Get the kind of name that is actually stored.
   NameKind getKind() const;
 
   /// Retrieve the underlying template declaration that
   /// this template name refers to, if known.
   ///
   /// \returns The template declaration that this template name refers
   /// to, if any. If the template name does not refer to a specific
   /// declaration because it is a dependent name, or if it refers to a
   /// set of function templates, returns NULL.
   TemplateDecl *getAsTemplateDecl(bool IgnoreDeduced = false) const;
 
   /// Retrieves the underlying template declaration that
   /// this template name refers to, along with the
   /// deduced default arguments, if any.
   std::pair<TemplateDecl *, DefaultArguments>
   getTemplateDeclAndDefaultArgs() const;
 
   /// Retrieve the underlying, overloaded function template
   /// declarations that this template name refers to, if known.
   ///
   /// \returns The set of overloaded function templates that this template
   /// name refers to, if known. If the template name does not refer to a
   /// specific set of function templates because it is a dependent name or
   /// refers to a single template, returns NULL.
   OverloadedTemplateStorage *getAsOverloadedTemplate() const;
 
   /// Retrieve information on a name that has been assumed to be a
   /// template-name in order to permit a call via ADL.
   AssumedTemplateStorage *getAsAssumedTemplateName() const;
 
   /// Retrieve the substituted template template parameter, if
   /// known.
   ///
   /// \returns The storage for the substituted template template parameter,
   /// if known. Otherwise, returns NULL.
   SubstTemplateTemplateParmStorage *getAsSubstTemplateTemplateParm() const;
 
   /// Retrieve the substituted template template parameter pack, if
   /// known.
   ///
   /// \returns The storage for the substituted template template parameter pack,
   /// if known. Otherwise, returns NULL.
   SubstTemplateTemplateParmPackStorage *
   getAsSubstTemplateTemplateParmPack() const;
 
   /// Retrieve the underlying qualified template name
   /// structure, if any.
   QualifiedTemplateName *getAsQualifiedTemplateName() const;
 
   /// Retrieve the underlying dependent template name
   /// structure, if any.
   DependentTemplateName *getAsDependentTemplateName() const;
 
   /// Retrieve the using shadow declaration through which the underlying
   /// template declaration is introduced, if any.
   UsingShadowDecl *getAsUsingShadowDecl() const;
 
   /// Retrieve the deduced template info, if any.
   DeducedTemplateStorage *getAsDeducedTemplateName() const;
 
   std::optional<TemplateName> desugar(bool IgnoreDeduced) const;
 
   TemplateName getUnderlying() const;
 
   TemplateNameDependence getDependence() const;
 
   /// Determines whether this is a dependent template name.
   bool isDependent() const;
 
   /// Determines whether this is a template name that somehow
   /// depends on a template parameter.
   bool isInstantiationDependent() const;
 
   /// Determines whether this template name contains an
   /// unexpanded parameter pack (for C++0x variadic templates).
   bool containsUnexpandedParameterPack() const;
 
   enum class Qualified { None, AsWritten };
   /// Print the template name.
   ///
   /// \param OS the output stream to which the template name will be
   /// printed.
   ///
   /// \param Qual print the (Qualified::None) simple name,
   /// (Qualified::AsWritten) any written (possibly partial) qualifier, or
   /// (Qualified::Fully) the fully qualified name.
   void print(raw_ostream &OS, const PrintingPolicy &Policy,
              Qualified Qual = Qualified::AsWritten) const;
 
   /// Debugging aid that dumps the template name.
   void dump(raw_ostream &OS, const ASTContext &Context) const;
 
   /// Debugging aid that dumps the template name to standard
   /// error.
   void dump() const;
 
   void Profile(llvm::FoldingSetNodeID &ID) {
     ID.AddPointer(Storage.getOpaqueValue());
   }
 
   /// Retrieve the template name as a void pointer.
   void *getAsVoidPointer() const { return Storage.getOpaqueValue(); }
 
   /// Build a template name from a void pointer.
   static TemplateName getFromVoidPointer(void *Ptr) {
     return TemplateName(Ptr);
   }
 
   /// Structural equality.
   bool operator==(TemplateName Other) const { return Storage == Other.Storage; }
   bool operator!=(TemplateName Other) const { return !operator==(Other); }
 };
 
 /// Insertion operator for diagnostics.  This allows sending TemplateName's
 /// into a diagnostic with <<.
 const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
                                       TemplateName N);
 
 /// A structure for storing the information associated with a
 /// substituted template template parameter.
 class SubstTemplateTemplateParmStorage
   : public UncommonTemplateNameStorage, public llvm::FoldingSetNode {
   friend class ASTContext;
 
   TemplateName Replacement;
   Decl *AssociatedDecl;
 
   SubstTemplateTemplateParmStorage(TemplateName Replacement,
                                    Decl *AssociatedDecl, unsigned Index,
                                    std::optional<unsigned> PackIndex)
       : UncommonTemplateNameStorage(SubstTemplateTemplateParm, Index,
                                     PackIndex ? *PackIndex + 1 : 0),
         Replacement(Replacement), AssociatedDecl(AssociatedDecl) {
     assert(AssociatedDecl != nullptr);
   }
 
 public:
   /// A template-like entity which owns the whole pattern being substituted.
   /// This will own a set of template parameters.
   Decl *getAssociatedDecl() const { return AssociatedDecl; }
 
   /// Returns the index of the replaced parameter in the associated declaration.
   /// This should match the result of `getParameter()->getIndex()`.
   unsigned getIndex() const { return Bits.Index; }
 
   std::optional<unsigned> getPackIndex() const {
     if (Bits.Data == 0)
       return std::nullopt;
     return Bits.Data - 1;
   }
 
   TemplateTemplateParmDecl *getParameter() const;
   TemplateName getReplacement() const { return Replacement; }
 
   void Profile(llvm::FoldingSetNodeID &ID);
 
   static void Profile(llvm::FoldingSetNodeID &ID, TemplateName Replacement,
                       Decl *AssociatedDecl, unsigned Index,
                       std::optional<unsigned> PackIndex);
 };
 
 class DeducedTemplateStorage : public UncommonTemplateNameStorage,
                                public llvm::FoldingSetNode {
   friend class ASTContext;
 
   TemplateName Underlying;
 
   DeducedTemplateStorage(TemplateName Underlying,
                          const DefaultArguments &DefArgs);
 
 public:
   TemplateName getUnderlying() const { return Underlying; }
 
   DefaultArguments getDefaultArguments() const {
     return {/*StartPos=*/Bits.Index,
             /*Args=*/{reinterpret_cast<const TemplateArgument *>(this + 1),
                       Bits.Data}};
   }
 
   void Profile(llvm::FoldingSetNodeID &ID, const ASTContext &Context) const;
 
   static void Profile(llvm::FoldingSetNodeID &ID, const ASTContext &Context,
                       TemplateName Underlying, const DefaultArguments &DefArgs);
 };
 
 inline TemplateName TemplateName::getUnderlying() const {
   if (SubstTemplateTemplateParmStorage *subst
         = getAsSubstTemplateTemplateParm())
     return subst->getReplacement().getUnderlying();
   return *this;
 }
 
 /// Represents a template name as written in source code.
 ///
 /// This kind of template name may refer to a template name that was
 /// preceded by a nested name specifier, e.g., \c std::vector. Here,
 /// the nested name specifier is "std::" and the template name is the
 /// declaration for "vector". It may also have been written with the
 /// 'template' keyword. The QualifiedTemplateName class is only
 /// used to provide "sugar" for template names, so that they can
 /// be differentiated from canonical template names. and has no
 /// semantic meaning. In this manner, it is to TemplateName what
 /// ElaboratedType is to Type, providing extra syntactic sugar
 /// for downstream clients.
 class QualifiedTemplateName : public llvm::FoldingSetNode {
   friend class ASTContext;
 
   /// The nested name specifier that qualifies the template name.
   ///
   /// The bit is used to indicate whether the "template" keyword was
   /// present before the template name itself. Note that the
   /// "template" keyword is always redundant in this case (otherwise,
   /// the template name would be a dependent name and we would express
   /// this name with DependentTemplateName).
   llvm::PointerIntPair<NestedNameSpecifier *, 1> Qualifier;
 
   /// The underlying template name, it is either
   ///  1) a Template -- a template declaration that this qualified name refers
   ///     to.
   ///  2) or a UsingTemplate -- a template declaration introduced by a
   ///     using-shadow declaration.
   TemplateName UnderlyingTemplate;
 
   QualifiedTemplateName(NestedNameSpecifier *NNS, bool TemplateKeyword,
                         TemplateName Template)
       : Qualifier(NNS, TemplateKeyword ? 1 : 0), UnderlyingTemplate(Template) {
     assert(UnderlyingTemplate.getKind() == TemplateName::Template ||
            UnderlyingTemplate.getKind() == TemplateName::UsingTemplate);
   }
 
 public:
   /// Return the nested name specifier that qualifies this name.
   NestedNameSpecifier *getQualifier() const { return Qualifier.getPointer(); }
 
   /// Whether the template name was prefixed by the "template"
   /// keyword.
   bool hasTemplateKeyword() const { return Qualifier.getInt(); }
 
   /// Return the underlying template name.
   TemplateName getUnderlyingTemplate() const { return UnderlyingTemplate; }
 
   void Profile(llvm::FoldingSetNodeID &ID) {
     Profile(ID, getQualifier(), hasTemplateKeyword(), UnderlyingTemplate);
   }
 
   static void Profile(llvm::FoldingSetNodeID &ID, NestedNameSpecifier *NNS,
                       bool TemplateKeyword, TemplateName TN) {
     ID.AddPointer(NNS);
     ID.AddBoolean(TemplateKeyword);
     ID.AddPointer(TN.getAsVoidPointer());
   }
 };
 
 /// Represents a dependent template name that cannot be
 /// resolved prior to template instantiation.
 ///
 /// This kind of template name refers to a dependent template name,
 /// including its nested name specifier (if any). For example,
 /// DependentTemplateName can refer to "MetaFun::template apply",
 /// where "MetaFun::" is the nested name specifier and "apply" is the
 /// template name referenced. The "template" keyword is implied.
 class DependentTemplateName : public llvm::FoldingSetNode {
   friend class ASTContext;
 
   /// The nested name specifier that qualifies the template
   /// name.
   ///
   /// The bit stored in this qualifier describes whether the \c Name field
   /// is interpreted as an IdentifierInfo pointer (when clear) or as an
   /// overloaded operator kind (when set).
   llvm::PointerIntPair<NestedNameSpecifier *, 1, bool> Qualifier;
 
   /// The dependent template name.
   union {
     /// The identifier template name.
     ///
     /// Only valid when the bit on \c Qualifier is clear.
     const IdentifierInfo *Identifier;
 
     /// The overloaded operator name.
     ///
     /// Only valid when the bit on \c Qualifier is set.
     OverloadedOperatorKind Operator;
   };
 
   /// The canonical template name to which this dependent
   /// template name refers.
   ///
   /// The canonical template name for a dependent template name is
   /// another dependent template name whose nested name specifier is
   /// canonical.
   TemplateName CanonicalTemplateName;
 
   DependentTemplateName(NestedNameSpecifier *Qualifier,
                         const IdentifierInfo *Identifier)
       : Qualifier(Qualifier, false), Identifier(Identifier),
         CanonicalTemplateName(this) {}
 
   DependentTemplateName(NestedNameSpecifier *Qualifier,
                         const IdentifierInfo *Identifier,
                         TemplateName Canon)
       : Qualifier(Qualifier, false), Identifier(Identifier),
         CanonicalTemplateName(Canon) {}
 
   DependentTemplateName(NestedNameSpecifier *Qualifier,
                         OverloadedOperatorKind Operator)
       : Qualifier(Qualifier, true), Operator(Operator),
         CanonicalTemplateName(this) {}
 
   DependentTemplateName(NestedNameSpecifier *Qualifier,
                         OverloadedOperatorKind Operator,
                         TemplateName Canon)
        : Qualifier(Qualifier, true), Operator(Operator),
          CanonicalTemplateName(Canon) {}
 
 public:
   /// Return the nested name specifier that qualifies this name.
   NestedNameSpecifier *getQualifier() const { return Qualifier.getPointer(); }
 
   /// Determine whether this template name refers to an identifier.
   bool isIdentifier() const { return !Qualifier.getInt(); }
 
   /// Returns the identifier to which this template name refers.
   const IdentifierInfo *getIdentifier() const {
     assert(isIdentifier() && "Template name isn't an identifier?");
     return Identifier;
   }
 
   /// Determine whether this template name refers to an overloaded
   /// operator.
   bool isOverloadedOperator() const { return Qualifier.getInt(); }
 
   /// Return the overloaded operator to which this template name refers.
   OverloadedOperatorKind getOperator() const {
     assert(isOverloadedOperator() &&
            "Template name isn't an overloaded operator?");
     return Operator;
   }
 
   void Profile(llvm::FoldingSetNodeID &ID) {
     if (isIdentifier())
       Profile(ID, getQualifier(), getIdentifier());
     else
       Profile(ID, getQualifier(), getOperator());
   }
 
   static void Profile(llvm::FoldingSetNodeID &ID, NestedNameSpecifier *NNS,
                       const IdentifierInfo *Identifier) {
     ID.AddPointer(NNS);
     ID.AddBoolean(false);
     ID.AddPointer(Identifier);
   }
 
   static void Profile(llvm::FoldingSetNodeID &ID, NestedNameSpecifier *NNS,
                       OverloadedOperatorKind Operator) {
     ID.AddPointer(NNS);
     ID.AddBoolean(true);
     ID.AddInteger(Operator);
   }
 };
 
 } // namespace clang.
 
 namespace llvm {
 
 /// The clang::TemplateName class is effectively a pointer.
 template<>
 struct PointerLikeTypeTraits<clang::TemplateName> {
   static inline void *getAsVoidPointer(clang::TemplateName TN) {
     return TN.getAsVoidPointer();
   }
 
   static inline clang::TemplateName getFromVoidPointer(void *Ptr) {
     return clang::TemplateName::getFromVoidPointer(Ptr);
   }
 
   // No bits are available!
   static constexpr int NumLowBitsAvailable = 0;
 };
 
 } // namespace llvm.
 
 #endif // LLVM_CLANG_AST_TEMPLATENAME_H

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