TemplateName.h

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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,