llvm/clang/include/clang/AST/DeclTemplate.h

//===- DeclTemplate.h - Classes for representing C++ templates --*- 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++ template declaration subclasses.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_AST_DECLTEMPLATE_H
#define LLVM_CLANG_AST_DECLTEMPLATE_H

#include "clang/AST/ASTConcept.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclBase.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclarationName.h"
#include "clang/AST/Redeclarable.h"
#include "clang/AST/TemplateBase.h"
#include "clang/AST/Type.h"
#include "clang/Basic/LLVM.h"
#include "clang/Basic/SourceLocation.h"
#include "clang/Basic/Specifiers.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/FoldingSet.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/PointerUnion.h"
#include "llvm/ADT/iterator.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/TrailingObjects.h"
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <optional>
#include <utility>

namespace clang {

enum BuiltinTemplateKind : int;
class ClassTemplateDecl;
class ClassTemplatePartialSpecializationDecl;
class Expr;
class FunctionTemplateDecl;
class IdentifierInfo;
class NonTypeTemplateParmDecl;
class TemplateDecl;
class TemplateTemplateParmDecl;
class TemplateTypeParmDecl;
class ConceptDecl;
class UnresolvedSetImpl;
class VarTemplateDecl;
class VarTemplatePartialSpecializationDecl;

/// Stores a template parameter of any kind.
TemplateParameter;

NamedDecl *getAsNamedDecl(TemplateParameter P);

/// Stores a list of template parameters for a TemplateDecl and its
/// derived classes.
class TemplateParameterList final
    : private llvm::TrailingObjects<TemplateParameterList, NamedDecl *,
                                    Expr *> { … };

/// Stores a list of template parameters and the associated
/// requires-clause (if any) for a TemplateDecl and its derived classes.
/// Suitable for creating on the stack.
template <size_t N, bool HasRequiresClause>
class FixedSizeTemplateParameterListStorage
    : public TemplateParameterList::FixedSizeStorageOwner { … };

/// A template argument list.
class TemplateArgumentList final
    : private llvm::TrailingObjects<TemplateArgumentList, TemplateArgument> { … };

void *allocateDefaultArgStorageChain(const ASTContext &C);

/// Storage for a default argument. This is conceptually either empty, or an
/// argument value, or a pointer to a previous declaration that had a default
/// argument.
///
/// However, this is complicated by modules: while we require all the default
/// arguments for a template to be equivalent, there may be more than one, and
/// we need to track all the originating parameters to determine if the default
/// argument is visible.
template<typename ParmDecl, typename ArgType>
class DefaultArgStorage { … };

//===----------------------------------------------------------------------===//
// Kinds of Templates
//===----------------------------------------------------------------------===//

/// \brief The base class of all kinds of template declarations (e.g.,
/// class, function, etc.).
///
/// The TemplateDecl class stores the list of template parameters and a
/// reference to the templated scoped declaration: the underlying AST node.
class TemplateDecl : public NamedDecl { … };

/// Provides information about a function template specialization,
/// which is a FunctionDecl that has been explicitly specialization or
/// instantiated from a function template.
class FunctionTemplateSpecializationInfo final
    : public llvm::FoldingSetNode,
      private llvm::TrailingObjects<FunctionTemplateSpecializationInfo,
                                    MemberSpecializationInfo *> { … };

/// Provides information a specialization of a member of a class
/// template, which may be a member function, static data member,
/// member class or member enumeration.
class MemberSpecializationInfo { … };

/// Provides information about a dependent function-template
/// specialization declaration.
///
/// This is used for function templates explicit specializations declared
/// within class templates:
///
/// \code
/// template<typename> struct A {
///   template<typename> void f();
///   template<> void f<int>(); // DependentFunctionTemplateSpecializationInfo
/// };
/// \endcode
///
/// As well as dependent friend declarations naming function template
/// specializations declared within class templates:
///
/// \code
///   template \<class T> void foo(T);
///   template \<class T> class A {
///     friend void foo<>(T); // DependentFunctionTemplateSpecializationInfo
///   };
/// \endcode
class DependentFunctionTemplateSpecializationInfo final
    : private llvm::TrailingObjects<DependentFunctionTemplateSpecializationInfo,
                                    FunctionTemplateDecl *> { … };

/// Declaration of a redeclarable template.
class RedeclarableTemplateDecl : public TemplateDecl,
                                 public Redeclarable<RedeclarableTemplateDecl>
{ … };

template <> struct RedeclarableTemplateDecl::
SpecEntryTraits<FunctionTemplateSpecializationInfo> { … };

/// Declaration of a template function.
class FunctionTemplateDecl : public RedeclarableTemplateDecl { … };

//===----------------------------------------------------------------------===//
// Kinds of Template Parameters
//===----------------------------------------------------------------------===//

/// Defines the position of a template parameter within a template
/// parameter list.
///
/// Because template parameter can be listed
/// sequentially for out-of-line template members, each template parameter is
/// given a Depth - the nesting of template parameter scopes - and a Position -
/// the occurrence within the parameter list.
/// This class is inheritedly privately by different kinds of template
/// parameters and is not part of the Decl hierarchy. Just a facility.
class TemplateParmPosition { … };

/// Declaration of a template type parameter.
///
/// For example, "T" in
/// \code
/// template<typename T> class vector;
/// \endcode
class TemplateTypeParmDecl final : public TypeDecl,
    private llvm::TrailingObjects<TemplateTypeParmDecl, TypeConstraint> { … };

/// NonTypeTemplateParmDecl - Declares a non-type template parameter,
/// e.g., "Size" in
/// @code
/// template<int Size> class array { };
/// @endcode
class NonTypeTemplateParmDecl final
    : public DeclaratorDecl,
      protected TemplateParmPosition,
      private llvm::TrailingObjects<NonTypeTemplateParmDecl,
                                    std::pair<QualType, TypeSourceInfo *>,
                                    Expr *> { … };

/// TemplateTemplateParmDecl - Declares a template template parameter,
/// e.g., "T" in
/// @code
/// template <template <typename> class T> class container { };
/// @endcode
/// A template template parameter is a TemplateDecl because it defines the
/// name of a template and the template parameters allowable for substitution.
class TemplateTemplateParmDecl final
    : public TemplateDecl,
      protected TemplateParmPosition,
      private llvm::TrailingObjects<TemplateTemplateParmDecl,
                                    TemplateParameterList *> { … };

/// Represents the builtin template declaration which is used to
/// implement __make_integer_seq and other builtin templates.  It serves
/// no real purpose beyond existing as a place to hold template parameters.
class BuiltinTemplateDecl : public TemplateDecl { … };

/// Provides information about an explicit instantiation of a variable or class
/// template.
struct ExplicitInstantiationInfo { … };

SpecializationOrInstantiationInfo;

/// Represents a class template specialization, which refers to
/// a class template with a given set of template arguments.
///
/// Class template specializations represent both explicit
/// specialization of class templates, as in the example below, and
/// implicit instantiations of class templates.
///
/// \code
/// template<typename T> class array;
///
/// template<>
/// class array<bool> { }; // class template specialization array<bool>
/// \endcode
class ClassTemplateSpecializationDecl : public CXXRecordDecl,
                                        public llvm::FoldingSetNode { … };

class ClassTemplatePartialSpecializationDecl
  : public ClassTemplateSpecializationDecl { … };

/// Declaration of a class template.
class ClassTemplateDecl : public RedeclarableTemplateDecl { … };

/// Declaration of a friend template.
///
/// For example:
/// \code
/// template \<typename T> class A {
///   friend class MyVector<T>; // not a friend template
///   template \<typename U> friend class B; // not a friend template
///   template \<typename U> friend class Foo<T>::Nested; // friend template
/// };
/// \endcode
///
/// \note This class is not currently in use.  All of the above
/// will yield a FriendDecl, not a FriendTemplateDecl.
class FriendTemplateDecl : public Decl { … };

/// Declaration of an alias template.
///
/// For example:
/// \code
/// template \<typename T> using V = std::map<T*, int, MyCompare<T>>;
/// \endcode
class TypeAliasTemplateDecl : public RedeclarableTemplateDecl { … };

/// Represents a variable template specialization, which refers to
/// a variable template with a given set of template arguments.
///
/// Variable template specializations represent both explicit
/// specializations of variable templates, as in the example below, and
/// implicit instantiations of variable templates.
///
/// \code
/// template<typename T> constexpr T pi = T(3.1415926535897932385);
///
/// template<>
/// constexpr float pi<float>; // variable template specialization pi<float>
/// \endcode
class VarTemplateSpecializationDecl : public VarDecl,
                                      public llvm::FoldingSetNode { … };

class VarTemplatePartialSpecializationDecl
    : public VarTemplateSpecializationDecl { … };

/// Declaration of a variable template.
class VarTemplateDecl : public RedeclarableTemplateDecl { … };

/// Declaration of a C++20 concept.
class ConceptDecl : public TemplateDecl, public Mergeable<ConceptDecl> { … };

// An implementation detail of ConceptSpecialicationExpr that holds the template
// arguments, so we can later use this to reconstitute the template arguments
// during constraint checking.
class ImplicitConceptSpecializationDecl final
    : public Decl,
      private llvm::TrailingObjects<ImplicitConceptSpecializationDecl,
                                    TemplateArgument> { … };

/// A template parameter object.
///
/// Template parameter objects represent values of class type used as template
/// arguments. There is one template parameter object for each such distinct
/// value used as a template argument across the program.
///
/// \code
/// struct A { int x, y; };
/// template<A> struct S;
/// S<A{1, 2}> s1;
/// S<A{1, 2}> s2; // same type, argument is same TemplateParamObjectDecl.
/// \endcode
class TemplateParamObjectDecl : public ValueDecl,
                                public Mergeable<TemplateParamObjectDecl>,
                                public llvm::FoldingSetNode { … };

inline NamedDecl *getAsNamedDecl(TemplateParameter P) { … }

inline TemplateDecl *getAsTypeTemplateDecl(Decl *D) { … }

/// Check whether the template parameter is a pack expansion, and if so,
/// determine the number of parameters produced by that expansion. For instance:
///
/// \code
/// template<typename ...Ts> struct A {
///   template<Ts ...NTs, template<Ts> class ...TTs, typename ...Us> struct B;
/// };
/// \endcode
///
/// In \c A<int,int>::B, \c NTs and \c TTs have expanded pack size 2, and \c Us
/// is not a pack expansion, so returns an empty Optional.
inline std::optional<unsigned> getExpandedPackSize(const NamedDecl *Param) { … }

/// Internal helper used by Subst* nodes to retrieve the parameter list
/// for their AssociatedDecl.
TemplateParameterList *getReplacedTemplateParameterList(Decl *D);

} // namespace clang

#endif // LLVM_CLANG_AST_DECLTEMPLATE_H