llvm-project/clang/lib/Sema/SemaTemplateInstantiate.cpp

//===------- SemaTemplateInstantiate.cpp - C++ Template Instantiation ------===/
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//===----------------------------------------------------------------------===/
//
//  This file implements C++ template instantiation.
//
//===----------------------------------------------------------------------===/

#include "Sema.h"
#include "TreeTransform.h"
#include "clang/AST/ASTConsumer.h"
#include "clang/AST/ASTContext.h"
#include "clang/AST/Expr.h"
#include "clang/AST/DeclTemplate.h"
#include "clang/Parse/DeclSpec.h"
#include "clang/Basic/LangOptions.h"
#include "llvm/Support/Compiler.h"

using namespace clang;

//===----------------------------------------------------------------------===/
// Template Instantiation Support
//===----------------------------------------------------------------------===/

/// \brief Retrieve the template argument list(s) that should be used to
/// instantiate the definition of the given declaration.
MultiLevelTemplateArgumentList
Sema::getTemplateInstantiationArgs(NamedDecl *D) {
  // Accumulate the set of template argument lists in this structure.
  MultiLevelTemplateArgumentList Result;
  
  DeclContext *Ctx = dyn_cast<DeclContext>(D);
  if (!Ctx)
    Ctx = D->getDeclContext();
  
  while (!Ctx->isFileContext()) {
    // Add template arguments from a class template instantiation.
    if (ClassTemplateSpecializationDecl *Spec 
          = dyn_cast<ClassTemplateSpecializationDecl>(Ctx)) {
      // We're done when we hit an explicit specialization.
      if (Spec->getSpecializationKind() == TSK_ExplicitSpecialization)
        break;
      
      Result.addOuterTemplateArguments(&Spec->getTemplateInstantiationArgs());
    } 
    
    // Add template arguments from a function template specialization.
    else if (FunctionDecl *Function = dyn_cast<FunctionDecl>(Ctx)) {
      // FIXME: Check whether this is an explicit specialization.
      if (const TemplateArgumentList *TemplateArgs
            = Function->getTemplateSpecializationArgs())
        Result.addOuterTemplateArguments(TemplateArgs);

      // If this is a friend declaration and it declares an entity at
      // namespace scope, take arguments from its lexical parent
      // instead of its semantic parent.
      if (Function->getFriendObjectKind() &&
          Function->getDeclContext()->isFileContext()) {
        Ctx = Function->getLexicalDeclContext();
        continue;
      }
    }

    Ctx = Ctx->getParent();
  }
  
  return Result;
}

Sema::InstantiatingTemplate::
InstantiatingTemplate(Sema &SemaRef, SourceLocation PointOfInstantiation,
                      Decl *Entity,
                      SourceRange InstantiationRange)
  :  SemaRef(SemaRef) {

  Invalid = CheckInstantiationDepth(PointOfInstantiation,
                                    InstantiationRange);
  if (!Invalid) {
    ActiveTemplateInstantiation Inst;
    Inst.Kind = ActiveTemplateInstantiation::TemplateInstantiation;
    Inst.PointOfInstantiation = PointOfInstantiation;
    Inst.Entity = reinterpret_cast<uintptr_t>(Entity);
    Inst.TemplateArgs = 0;
    Inst.NumTemplateArgs = 0;
    Inst.InstantiationRange = InstantiationRange;
    SemaRef.ActiveTemplateInstantiations.push_back(Inst);
    Invalid = false;
  }
}

Sema::InstantiatingTemplate::InstantiatingTemplate(Sema &SemaRef, 
                                         SourceLocation PointOfInstantiation,
                                         TemplateDecl *Template,
                                         const TemplateArgument *TemplateArgs,
                                         unsigned NumTemplateArgs,
                                         SourceRange InstantiationRange)
  : SemaRef(SemaRef) {

  Invalid = CheckInstantiationDepth(PointOfInstantiation,
                                    InstantiationRange);
  if (!Invalid) {
    ActiveTemplateInstantiation Inst;
    Inst.Kind 
      = ActiveTemplateInstantiation::DefaultTemplateArgumentInstantiation;
    Inst.PointOfInstantiation = PointOfInstantiation;
    Inst.Entity = reinterpret_cast<uintptr_t>(Template);
    Inst.TemplateArgs = TemplateArgs;
    Inst.NumTemplateArgs = NumTemplateArgs;
    Inst.InstantiationRange = InstantiationRange;
    SemaRef.ActiveTemplateInstantiations.push_back(Inst);
    Invalid = false;
  }
}

Sema::InstantiatingTemplate::InstantiatingTemplate(Sema &SemaRef, 
                                         SourceLocation PointOfInstantiation,
                                      FunctionTemplateDecl *FunctionTemplate,
                                        const TemplateArgument *TemplateArgs,
                                                   unsigned NumTemplateArgs,
                         ActiveTemplateInstantiation::InstantiationKind Kind,
                                              SourceRange InstantiationRange)
: SemaRef(SemaRef) {
  
  Invalid = CheckInstantiationDepth(PointOfInstantiation,
                                    InstantiationRange);
  if (!Invalid) {
    ActiveTemplateInstantiation Inst;
    Inst.Kind = Kind;
    Inst.PointOfInstantiation = PointOfInstantiation;
    Inst.Entity = reinterpret_cast<uintptr_t>(FunctionTemplate);
    Inst.TemplateArgs = TemplateArgs;
    Inst.NumTemplateArgs = NumTemplateArgs;
    Inst.InstantiationRange = InstantiationRange;
    SemaRef.ActiveTemplateInstantiations.push_back(Inst);
    Invalid = false;
  }
}

Sema::InstantiatingTemplate::InstantiatingTemplate(Sema &SemaRef, 
                                         SourceLocation PointOfInstantiation,
                          ClassTemplatePartialSpecializationDecl *PartialSpec,
                                         const TemplateArgument *TemplateArgs,
                                         unsigned NumTemplateArgs,
                                         SourceRange InstantiationRange)
  : SemaRef(SemaRef) {

  Invalid = CheckInstantiationDepth(PointOfInstantiation,
                                    InstantiationRange);
  if (!Invalid) {
    ActiveTemplateInstantiation Inst;
    Inst.Kind 
      = ActiveTemplateInstantiation::DeducedTemplateArgumentSubstitution;
    Inst.PointOfInstantiation = PointOfInstantiation;
    Inst.Entity = reinterpret_cast<uintptr_t>(PartialSpec);
    Inst.TemplateArgs = TemplateArgs;
    Inst.NumTemplateArgs = NumTemplateArgs;
    Inst.InstantiationRange = InstantiationRange;
    SemaRef.ActiveTemplateInstantiations.push_back(Inst);
    Invalid = false;
  }
}

void Sema::InstantiatingTemplate::Clear() {
  if (!Invalid) {
    SemaRef.ActiveTemplateInstantiations.pop_back();
    Invalid = true;
  }
}

bool Sema::InstantiatingTemplate::CheckInstantiationDepth(
                                        SourceLocation PointOfInstantiation,
                                           SourceRange InstantiationRange) {
  if (SemaRef.ActiveTemplateInstantiations.size() 
       <= SemaRef.getLangOptions().InstantiationDepth)
    return false;

  SemaRef.Diag(PointOfInstantiation, 
               diag::err_template_recursion_depth_exceeded)
    << SemaRef.getLangOptions().InstantiationDepth
    << InstantiationRange;
  SemaRef.Diag(PointOfInstantiation, diag::note_template_recursion_depth)
    << SemaRef.getLangOptions().InstantiationDepth;
  return true;
}

/// \brief Prints the current instantiation stack through a series of
/// notes.
void Sema::PrintInstantiationStack() {
  // FIXME: In all of these cases, we need to show the template arguments
  for (llvm::SmallVector<ActiveTemplateInstantiation, 16>::reverse_iterator
         Active = ActiveTemplateInstantiations.rbegin(),
         ActiveEnd = ActiveTemplateInstantiations.rend();
       Active != ActiveEnd;
       ++Active) {
    switch (Active->Kind) {
    case ActiveTemplateInstantiation::TemplateInstantiation: {
      Decl *D = reinterpret_cast<Decl *>(Active->Entity);
      if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(D)) {
        unsigned DiagID = diag::note_template_member_class_here;
        if (isa<ClassTemplateSpecializationDecl>(Record))
          DiagID = diag::note_template_class_instantiation_here;
        Diags.Report(FullSourceLoc(Active->PointOfInstantiation, SourceMgr), 
                     DiagID)
          << Context.getTypeDeclType(Record)
          << Active->InstantiationRange;
      } else if (FunctionDecl *Function = dyn_cast<FunctionDecl>(D)) {
        unsigned DiagID;
        if (Function->getPrimaryTemplate())
          DiagID = diag::note_function_template_spec_here;
        else
          DiagID = diag::note_template_member_function_here;
        Diags.Report(FullSourceLoc(Active->PointOfInstantiation, SourceMgr), 
                     DiagID)
          << Function
          << Active->InstantiationRange;
      } else {
        Diags.Report(FullSourceLoc(Active->PointOfInstantiation, SourceMgr),
                     diag::note_template_static_data_member_def_here)
          << cast<VarDecl>(D)
          << Active->InstantiationRange;
      }
      break;
    }

    case ActiveTemplateInstantiation::DefaultTemplateArgumentInstantiation: {
      TemplateDecl *Template = cast<TemplateDecl>((Decl *)Active->Entity);
      std::string TemplateArgsStr
        = TemplateSpecializationType::PrintTemplateArgumentList(
                                                         Active->TemplateArgs, 
                                                      Active->NumTemplateArgs,
                                                      Context.PrintingPolicy);
      Diags.Report(FullSourceLoc(Active->PointOfInstantiation, SourceMgr),
                   diag::note_default_arg_instantiation_here)
        << (Template->getNameAsString() + TemplateArgsStr)
        << Active->InstantiationRange;
      break;
    }

    case ActiveTemplateInstantiation::ExplicitTemplateArgumentSubstitution: {
      FunctionTemplateDecl *FnTmpl 
        = cast<FunctionTemplateDecl>((Decl *)Active->Entity);
      Diags.Report(FullSourceLoc(Active->PointOfInstantiation, SourceMgr),
                   diag::note_explicit_template_arg_substitution_here)
        << FnTmpl << Active->InstantiationRange;
      break;
    }
        
    case ActiveTemplateInstantiation::DeducedTemplateArgumentSubstitution:
      if (ClassTemplatePartialSpecializationDecl *PartialSpec
            = dyn_cast<ClassTemplatePartialSpecializationDecl>(
                                                    (Decl *)Active->Entity)) {
        Diags.Report(FullSourceLoc(Active->PointOfInstantiation, SourceMgr),
                     diag::note_partial_spec_deduct_instantiation_here)
          << Context.getTypeDeclType(PartialSpec)
          << Active->InstantiationRange;
      } else {
        FunctionTemplateDecl *FnTmpl
          = cast<FunctionTemplateDecl>((Decl *)Active->Entity);
        Diags.Report(FullSourceLoc(Active->PointOfInstantiation, SourceMgr),
                     diag::note_function_template_deduction_instantiation_here)
          << FnTmpl << Active->InstantiationRange;
      }
      break;

    }
  }
}

bool Sema::isSFINAEContext() const {
  using llvm::SmallVector;
  for (SmallVector<ActiveTemplateInstantiation, 16>::const_reverse_iterator
         Active = ActiveTemplateInstantiations.rbegin(),
         ActiveEnd = ActiveTemplateInstantiations.rend();
       Active != ActiveEnd;
       ++Active) {

    switch(Active->Kind) {
    case ActiveTemplateInstantiation::TemplateInstantiation:
      // This is a template instantiation, so there is no SFINAE.
      return false;
        
    case ActiveTemplateInstantiation::DefaultTemplateArgumentInstantiation:
      // A default template argument instantiation may or may not be a
      // SFINAE context; look further up the stack.
      break;
        
    case ActiveTemplateInstantiation::ExplicitTemplateArgumentSubstitution:
    case ActiveTemplateInstantiation::DeducedTemplateArgumentSubstitution:
      // We're either substitution explicitly-specified template arguments
      // or deduced template arguments, so SFINAE applies.
      return true;
    }
  }

  return false;
}

//===----------------------------------------------------------------------===/
// Template Instantiation for Types
//===----------------------------------------------------------------------===/
namespace {
  class VISIBILITY_HIDDEN TemplateInstantiator 
    : public TreeTransform<TemplateInstantiator> 
  {
    const MultiLevelTemplateArgumentList &TemplateArgs;
    SourceLocation Loc;
    DeclarationName Entity;

  public:
    typedef TreeTransform<TemplateInstantiator> inherited;
    
    TemplateInstantiator(Sema &SemaRef, 
                         const MultiLevelTemplateArgumentList &TemplateArgs,
                         SourceLocation Loc,
                         DeclarationName Entity) 
      : inherited(SemaRef), TemplateArgs(TemplateArgs), Loc(Loc), 
        Entity(Entity) { }

    /// \brief Determine whether the given type \p T has already been 
    /// transformed.
    ///
    /// For the purposes of template instantiation, a type has already been
    /// transformed if it is NULL or if it is not dependent.
    bool AlreadyTransformed(QualType T) {
      return T.isNull() || !T->isDependentType();
    }
        
    /// \brief Returns the location of the entity being instantiated, if known.
    SourceLocation getBaseLocation() { return Loc; }
    
    /// \brief Returns the name of the entity being instantiated, if any.
    DeclarationName getBaseEntity() { return Entity; }
    
    /// \brief Transform the given declaration by instantiating a reference to
    /// this declaration.
    Decl *TransformDecl(Decl *D);

    /// \brief Transform the definition of the given declaration by 
    /// instantiating it.
    Decl *TransformDefinition(Decl *D);
    
    /// \brief Rebuild the exception declaration and register the declaration
    /// as an instantiated local.
    VarDecl *RebuildExceptionDecl(VarDecl *ExceptionDecl, QualType T, 
                                  DeclaratorInfo *Declarator,
                                  IdentifierInfo *Name,
                                  SourceLocation Loc, SourceRange TypeRange);
    
    Sema::OwningExprResult TransformDeclRefExpr(DeclRefExpr *E);
    
    /// \brief Transforms a template type parameter type by performing 
    /// substitution of the corresponding template type argument.
    QualType TransformTemplateTypeParmType(const TemplateTypeParmType *T);
  };
}

Decl *TemplateInstantiator::TransformDecl(Decl *D) {
  if (!D)
    return 0;
  
  if (TemplateTemplateParmDecl *TTP = dyn_cast<TemplateTemplateParmDecl>(D)) {
    if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
      assert(TemplateArgs(TTP->getDepth(), TTP->getPosition()).getAsDecl() &&
             "Wrong kind of template template argument");
      return cast<TemplateDecl>(TemplateArgs(TTP->getDepth(), 
                                             TTP->getPosition()).getAsDecl());
    }
    
    // If the corresponding template argument is NULL or non-existent, it's 
    // because we are performing instantiation from explicitly-specified 
    // template arguments in a function template, but there were some
    // arguments left unspecified.
    if (!TemplateArgs.hasTemplateArgument(TTP->getDepth(), 
                                          TTP->getPosition()))
      return D;
    
    // FIXME: Implement depth reduction of template template parameters
    assert(false && 
      "Reducing depth of template template parameters is not yet implemented");
  }
  
  return SemaRef.FindInstantiatedDecl(cast<NamedDecl>(D));
}

Decl *TemplateInstantiator::TransformDefinition(Decl *D) {
  Decl *Inst = getSema().SubstDecl(D, getSema().CurContext, TemplateArgs);
  if (!Inst)
    return 0;
  
  getSema().CurrentInstantiationScope->InstantiatedLocal(D, Inst);
  return Inst;
}

VarDecl *
TemplateInstantiator::RebuildExceptionDecl(VarDecl *ExceptionDecl,
                                           QualType T, 
                                           DeclaratorInfo *Declarator,
                                           IdentifierInfo *Name,
                                           SourceLocation Loc, 
                                           SourceRange TypeRange) {
  VarDecl *Var = inherited::RebuildExceptionDecl(ExceptionDecl, T, Declarator,
                                                 Name, Loc, TypeRange);
  if (Var && !Var->isInvalidDecl())
    getSema().CurrentInstantiationScope->InstantiatedLocal(ExceptionDecl, Var);
  return Var;
}

Sema::OwningExprResult 
TemplateInstantiator::TransformDeclRefExpr(DeclRefExpr *E) {
  // FIXME: Clean this up a bit
  NamedDecl *D = E->getDecl();
  if (NonTypeTemplateParmDecl *NTTP = dyn_cast<NonTypeTemplateParmDecl>(D)) {
    if (NTTP->getDepth() >= TemplateArgs.getNumLevels()) {
      assert(false && "Cannot reduce non-type template parameter depth yet");
      return getSema().ExprError();
    }
    
    // If the corresponding template argument is NULL or non-existent, it's 
    // because we are performing instantiation from explicitly-specified 
    // template arguments in a function template, but there were some
    // arguments left unspecified.
    if (!TemplateArgs.hasTemplateArgument(NTTP->getDepth(), 
                                          NTTP->getPosition()))
      return SemaRef.Owned(E->Retain());
    
    const TemplateArgument &Arg = TemplateArgs(NTTP->getDepth(), 
                                               NTTP->getPosition());
    
    // The template argument itself might be an expression, in which
    // case we just return that expression.
    if (Arg.getKind() == TemplateArgument::Expression)
      return SemaRef.Owned(Arg.getAsExpr()->Retain());
    
    if (Arg.getKind() == TemplateArgument::Declaration) {
      ValueDecl *VD = cast<ValueDecl>(Arg.getAsDecl());
      
      VD = cast_or_null<ValueDecl>(getSema().FindInstantiatedDecl(VD));
      if (!VD)
        return SemaRef.ExprError();
      
      return SemaRef.BuildDeclRefExpr(VD, VD->getType(), E->getLocation(), 
                                      /*FIXME:*/false, /*FIXME:*/false);
    }
    
    assert(Arg.getKind() == TemplateArgument::Integral);
    QualType T = Arg.getIntegralType();
    if (T->isCharType() || T->isWideCharType())
      return SemaRef.Owned(new (SemaRef.Context) CharacterLiteral(
                                            Arg.getAsIntegral()->getZExtValue(),
                                            T->isWideCharType(),
                                            T, 
                                            E->getSourceRange().getBegin()));
    if (T->isBooleanType())
      return SemaRef.Owned(new (SemaRef.Context) CXXBoolLiteralExpr(
                                          Arg.getAsIntegral()->getBoolValue(),
                                          T, 
                                          E->getSourceRange().getBegin()));
    
    assert(Arg.getAsIntegral()->getBitWidth() == SemaRef.Context.getIntWidth(T));
    return SemaRef.Owned(new (SemaRef.Context) IntegerLiteral(
                                              *Arg.getAsIntegral(),
                                              T, 
                                              E->getSourceRange().getBegin()));
  }
  
  NamedDecl *InstD = SemaRef.FindInstantiatedDecl(D);
  if (!InstD)
    return SemaRef.ExprError();
  
  // If we instantiated an UnresolvedUsingDecl and got back an UsingDecl,
  // we need to get the underlying decl. 
  // FIXME: Is this correct? Maybe FindInstantiatedDecl should do this?
  InstD = InstD->getUnderlyingDecl();
  
  // FIXME: nested-name-specifier for QualifiedDeclRefExpr
  return SemaRef.BuildDeclarationNameExpr(E->getLocation(), InstD, 
                                          /*FIXME:*/false,
                                          /*FIXME:*/0, 
                                          /*FIXME:*/false);  
}

QualType 
TemplateInstantiator::TransformTemplateTypeParmType(
                                              const TemplateTypeParmType *T) {
  if (T->getDepth() < TemplateArgs.getNumLevels()) {
    // Replace the template type parameter with its corresponding
    // template argument.
    
    // If the corresponding template argument is NULL or doesn't exist, it's 
    // because we are performing instantiation from explicitly-specified 
    // template arguments in a function template class, but there were some 
    // arguments left unspecified.
    if (!TemplateArgs.hasTemplateArgument(T->getDepth(), T->getIndex()))
      return QualType(T, 0);
    
    assert(TemplateArgs(T->getDepth(), T->getIndex()).getKind() 
             == TemplateArgument::Type &&
           "Template argument kind mismatch");

    return TemplateArgs(T->getDepth(), T->getIndex()).getAsType();
  } 

  // The template type parameter comes from an inner template (e.g.,
  // the template parameter list of a member template inside the
  // template we are instantiating). Create a new template type
  // parameter with the template "level" reduced by one.
  return getSema().Context.getTemplateTypeParmType(
                                  T->getDepth() - TemplateArgs.getNumLevels(),
                                                   T->getIndex(),
                                                   T->isParameterPack(),
                                                   T->getName());
}

/// \brief Perform substitution on the type T with a given set of template
/// arguments.
///
/// This routine substitutes the given template arguments into the
/// type T and produces the instantiated type.
///
/// \param T the type into which the template arguments will be
/// substituted. If this type is not dependent, it will be returned
/// immediately.
///
/// \param TemplateArgs the template arguments that will be
/// substituted for the top-level template parameters within T.
///
/// \param Loc the location in the source code where this substitution
/// is being performed. It will typically be the location of the
/// declarator (if we're instantiating the type of some declaration)
/// or the location of the type in the source code (if, e.g., we're
/// instantiating the type of a cast expression).
///
/// \param Entity the name of the entity associated with a declaration
/// being instantiated (if any). May be empty to indicate that there
/// is no such entity (if, e.g., this is a type that occurs as part of
/// a cast expression) or that the entity has no name (e.g., an
/// unnamed function parameter).
///
/// \returns If the instantiation succeeds, the instantiated
/// type. Otherwise, produces diagnostics and returns a NULL type.
QualType Sema::SubstType(QualType T, 
                         const MultiLevelTemplateArgumentList &TemplateArgs,
                         SourceLocation Loc, DeclarationName Entity) {
  assert(!ActiveTemplateInstantiations.empty() &&
         "Cannot perform an instantiation without some context on the "
         "instantiation stack");

  // If T is not a dependent type, there is nothing to do.
  if (!T->isDependentType())
    return T;

  TemplateInstantiator Instantiator(*this, TemplateArgs, Loc, Entity);
  return Instantiator.TransformType(T);
}

/// \brief Perform substitution on the base class specifiers of the
/// given class template specialization.
///
/// Produces a diagnostic and returns true on error, returns false and
/// attaches the instantiated base classes to the class template
/// specialization if successful.
bool 
Sema::SubstBaseSpecifiers(CXXRecordDecl *Instantiation,
                          CXXRecordDecl *Pattern,
                          const MultiLevelTemplateArgumentList &TemplateArgs) {
  bool Invalid = false;
  llvm::SmallVector<CXXBaseSpecifier*, 4> InstantiatedBases;
  for (ClassTemplateSpecializationDecl::base_class_iterator 
         Base = Pattern->bases_begin(), BaseEnd = Pattern->bases_end();
       Base != BaseEnd; ++Base) {
    if (!Base->getType()->isDependentType()) {
      InstantiatedBases.push_back(new (Context) CXXBaseSpecifier(*Base));
      continue;
    }

    QualType BaseType = SubstType(Base->getType(), 
                                  TemplateArgs, 
                                  Base->getSourceRange().getBegin(),
                                  DeclarationName());
    if (BaseType.isNull()) {
      Invalid = true;
      continue;
    }

    if (CXXBaseSpecifier *InstantiatedBase
          = CheckBaseSpecifier(Instantiation,
                               Base->getSourceRange(),
                               Base->isVirtual(),
                               Base->getAccessSpecifierAsWritten(),
                               BaseType,
                               /*FIXME: Not totally accurate */
                               Base->getSourceRange().getBegin()))
      InstantiatedBases.push_back(InstantiatedBase);
    else
      Invalid = true;
  }

  if (!Invalid &&
      AttachBaseSpecifiers(Instantiation, InstantiatedBases.data(),
                           InstantiatedBases.size()))
    Invalid = true;

  return Invalid;
}

/// \brief Instantiate the definition of a class from a given pattern.
///
/// \param PointOfInstantiation The point of instantiation within the
/// source code.
///
/// \param Instantiation is the declaration whose definition is being
/// instantiated. This will be either a class template specialization
/// or a member class of a class template specialization.
///
/// \param Pattern is the pattern from which the instantiation
/// occurs. This will be either the declaration of a class template or
/// the declaration of a member class of a class template.
///
/// \param TemplateArgs The template arguments to be substituted into
/// the pattern.
///
/// \param TSK the kind of implicit or explicit instantiation to perform.
///
/// \param Complain whether to complain if the class cannot be instantiated due
/// to the lack of a definition.
///
/// \returns true if an error occurred, false otherwise.
bool
Sema::InstantiateClass(SourceLocation PointOfInstantiation,
                       CXXRecordDecl *Instantiation, CXXRecordDecl *Pattern,
                       const MultiLevelTemplateArgumentList &TemplateArgs,
                       TemplateSpecializationKind TSK,
                       bool Complain) {
  bool Invalid = false;

  CXXRecordDecl *PatternDef 
    = cast_or_null<CXXRecordDecl>(Pattern->getDefinition(Context));
  if (!PatternDef) {
    if (!Complain) {
      // Say nothing
    } else if (Pattern == Instantiation->getInstantiatedFromMemberClass()) {
      Diag(PointOfInstantiation,
           diag::err_implicit_instantiate_member_undefined)
        << Context.getTypeDeclType(Instantiation);
      Diag(Pattern->getLocation(), diag::note_member_of_template_here);
    } else {
      Diag(PointOfInstantiation, diag::err_template_instantiate_undefined)
        << (TSK != TSK_ImplicitInstantiation)
        << Context.getTypeDeclType(Instantiation);
      Diag(Pattern->getLocation(), diag::note_template_decl_here);
    }
    return true;
  }
  Pattern = PatternDef;

  InstantiatingTemplate Inst(*this, PointOfInstantiation, Instantiation);
  if (Inst)
    return true;

  // Enter the scope of this instantiation. We don't use
  // PushDeclContext because we don't have a scope.
  DeclContext *PreviousContext = CurContext;
  CurContext = Instantiation;

  // Start the definition of this instantiation.
  Instantiation->startDefinition();

  // Do substitution on the base class specifiers.
  if (SubstBaseSpecifiers(Instantiation, Pattern, TemplateArgs))
    Invalid = true;

  llvm::SmallVector<DeclPtrTy, 4> Fields;
  for (RecordDecl::decl_iterator Member = Pattern->decls_begin(),
         MemberEnd = Pattern->decls_end(); 
       Member != MemberEnd; ++Member) {
    Decl *NewMember = SubstDecl(*Member, Instantiation, TemplateArgs);
    if (NewMember) {
      if (NewMember->isInvalidDecl())
        Invalid = true;
      else if (FieldDecl *Field = dyn_cast<FieldDecl>(NewMember))
        Fields.push_back(DeclPtrTy::make(Field));
      else if (UsingDecl *UD = dyn_cast<UsingDecl>(NewMember))
        Instantiation->addDecl(UD);
    } else {
      // FIXME: Eventually, a NULL return will mean that one of the
      // instantiations was a semantic disaster, and we'll want to set Invalid =
      // true. For now, we expect to skip some members that we can't yet handle.
    }
  }

  // Finish checking fields.
  ActOnFields(0, Instantiation->getLocation(), DeclPtrTy::make(Instantiation),
              Fields.data(), Fields.size(), SourceLocation(), SourceLocation(),
              0);

  // Add any implicitly-declared members that we might need.
  AddImplicitlyDeclaredMembersToClass(Instantiation);

  // Exit the scope of this instantiation.
  CurContext = PreviousContext;

  if (!Invalid)
    Consumer.HandleTagDeclDefinition(Instantiation);

  // If this is an explicit instantiation, instantiate our members, too.
  if (!Invalid && TSK != TSK_ImplicitInstantiation) {
    Inst.Clear();
    InstantiateClassMembers(PointOfInstantiation, Instantiation, TemplateArgs,
                            TSK);
  }

  return Invalid;
}

bool 
Sema::InstantiateClassTemplateSpecialization(
                           ClassTemplateSpecializationDecl *ClassTemplateSpec,
                           TemplateSpecializationKind TSK,
                           bool Complain) {
  // Perform the actual instantiation on the canonical declaration.
  ClassTemplateSpec = cast<ClassTemplateSpecializationDecl>(
                                         ClassTemplateSpec->getCanonicalDecl());

  // We can only instantiate something that hasn't already been
  // instantiated or specialized. Fail without any diagnostics: our
  // caller will provide an error message.
  if (ClassTemplateSpec->getSpecializationKind() != TSK_Undeclared)
    return true;

  ClassTemplateDecl *Template = ClassTemplateSpec->getSpecializedTemplate();
  CXXRecordDecl *Pattern = 0;

  // C++ [temp.class.spec.match]p1:
  //   When a class template is used in a context that requires an
  //   instantiation of the class, it is necessary to determine
  //   whether the instantiation is to be generated using the primary
  //   template or one of the partial specializations. This is done by
  //   matching the template arguments of the class template
  //   specialization with the template argument lists of the partial
  //   specializations.
  typedef std::pair<ClassTemplatePartialSpecializationDecl *,
                    TemplateArgumentList *> MatchResult;
  llvm::SmallVector<MatchResult, 4> Matched;
  for (llvm::FoldingSet<ClassTemplatePartialSpecializationDecl>::iterator 
         Partial = Template->getPartialSpecializations().begin(),
         PartialEnd = Template->getPartialSpecializations().end();
       Partial != PartialEnd;
       ++Partial) {
    TemplateDeductionInfo Info(Context);
    if (TemplateDeductionResult Result
          = DeduceTemplateArguments(&*Partial, 
                                    ClassTemplateSpec->getTemplateArgs(),
                                    Info)) {
      // FIXME: Store the failed-deduction information for use in
      // diagnostics, later.
      (void)Result;
    } else {
      Matched.push_back(std::make_pair(&*Partial, Info.take()));
    }
  }

  if (Matched.size() == 1) {
    //   -- If exactly one matching specialization is found, the
    //      instantiation is generated from that specialization.
    Pattern = Matched[0].first;
    ClassTemplateSpec->setInstantiationOf(Matched[0].first, Matched[0].second);
  } else if (Matched.size() > 1) {
    //   -- If more than one matching specialization is found, the
    //      partial order rules (14.5.4.2) are used to determine
    //      whether one of the specializations is more specialized
    //      than the others. If none of the specializations is more
    //      specialized than all of the other matching
    //      specializations, then the use of the class template is
    //      ambiguous and the program is ill-formed.
    // FIXME: Implement partial ordering of class template partial
    // specializations.
    Diag(ClassTemplateSpec->getLocation(), 
         diag::unsup_template_partial_spec_ordering);

    // FIXME: Temporary hack to fall back to the primary template
    ClassTemplateDecl *OrigTemplate = Template;
    while (OrigTemplate->getInstantiatedFromMemberTemplate())
      OrigTemplate = OrigTemplate->getInstantiatedFromMemberTemplate();
    
    Pattern = OrigTemplate->getTemplatedDecl();
  } else {
    //   -- If no matches are found, the instantiation is generated
    //      from the primary template.
    ClassTemplateDecl *OrigTemplate = Template;
    while (OrigTemplate->getInstantiatedFromMemberTemplate())
      OrigTemplate = OrigTemplate->getInstantiatedFromMemberTemplate();
    
    Pattern = OrigTemplate->getTemplatedDecl();
  }

  // Note that this is an instantiation.
  ClassTemplateSpec->setSpecializationKind(TSK);

  bool Result = InstantiateClass(ClassTemplateSpec->getLocation(),
                                 ClassTemplateSpec, Pattern, 
                              getTemplateInstantiationArgs(ClassTemplateSpec),
                                 TSK,
                                 Complain);
  
  for (unsigned I = 0, N = Matched.size(); I != N; ++I) {
    // FIXME: Implement TemplateArgumentList::Destroy!
    //    if (Matched[I].first != Pattern)
    //      Matched[I].second->Destroy(Context);
  }
  
  return Result;
}

/// \brief Instantiates the definitions of all of the member
/// of the given class, which is an instantiation of a class template
/// or a member class of a template.
void
Sema::InstantiateClassMembers(SourceLocation PointOfInstantiation,
                              CXXRecordDecl *Instantiation,
                        const MultiLevelTemplateArgumentList &TemplateArgs,
                              TemplateSpecializationKind TSK) {
  // FIXME: extern templates
  for (DeclContext::decl_iterator D = Instantiation->decls_begin(),
                               DEnd = Instantiation->decls_end();
       D != DEnd; ++D) {
    if (FunctionDecl *Function = dyn_cast<FunctionDecl>(*D)) {
      if (!Function->getBody())
        InstantiateFunctionDefinition(PointOfInstantiation, Function);
    } else if (VarDecl *Var = dyn_cast<VarDecl>(*D)) {
      if (Var->isStaticDataMember())
        InstantiateStaticDataMemberDefinition(PointOfInstantiation, Var);
    } else if (CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(*D)) {
      if (!Record->isInjectedClassName() && !Record->getDefinition(Context)) {
        assert(Record->getInstantiatedFromMemberClass() && 
               "Missing instantiated-from-template information");
        InstantiateClass(PointOfInstantiation, Record,
                         Record->getInstantiatedFromMemberClass(),
                         TemplateArgs,
                         TSK);
      }
    }
  }
}

/// \brief Instantiate the definitions of all of the members of the
/// given class template specialization, which was named as part of an
/// explicit instantiation.
void 
Sema::InstantiateClassTemplateSpecializationMembers(
                                           SourceLocation PointOfInstantiation,
                            ClassTemplateSpecializationDecl *ClassTemplateSpec,
                                               TemplateSpecializationKind TSK) {
  // C++0x [temp.explicit]p7:
  //   An explicit instantiation that names a class template
  //   specialization is an explicit instantion of the same kind
  //   (declaration or definition) of each of its members (not
  //   including members inherited from base classes) that has not
  //   been previously explicitly specialized in the translation unit
  //   containing the explicit instantiation, except as described
  //   below.
  InstantiateClassMembers(PointOfInstantiation, ClassTemplateSpec,
                          getTemplateInstantiationArgs(ClassTemplateSpec),
                          TSK);
}

Sema::OwningStmtResult 
Sema::SubstStmt(Stmt *S, const MultiLevelTemplateArgumentList &TemplateArgs) {
  if (!S)
    return Owned(S);

  TemplateInstantiator Instantiator(*this, TemplateArgs,
                                    SourceLocation(),
                                    DeclarationName());
  return Instantiator.TransformStmt(S);
}

Sema::OwningExprResult 
Sema::SubstExpr(Expr *E, const MultiLevelTemplateArgumentList &TemplateArgs) {
  if (!E)
    return Owned(E);
  
  TemplateInstantiator Instantiator(*this, TemplateArgs,
                                    SourceLocation(),
                                    DeclarationName());
  return Instantiator.TransformExpr(E);
}

/// \brief Do template substitution on a nested-name-specifier.
NestedNameSpecifier *
Sema::SubstNestedNameSpecifier(NestedNameSpecifier *NNS,
                               SourceRange Range,
                         const MultiLevelTemplateArgumentList &TemplateArgs) {
  TemplateInstantiator Instantiator(*this, TemplateArgs, Range.getBegin(),
                                    DeclarationName());
  return Instantiator.TransformNestedNameSpecifier(NNS, Range);
}

TemplateName
Sema::SubstTemplateName(TemplateName Name, SourceLocation Loc,
                        const MultiLevelTemplateArgumentList &TemplateArgs) {
  TemplateInstantiator Instantiator(*this, TemplateArgs, Loc,
                                    DeclarationName());
  return Instantiator.TransformTemplateName(Name);
}

TemplateArgument Sema::Subst(TemplateArgument Arg, 
                         const MultiLevelTemplateArgumentList &TemplateArgs) {
  TemplateInstantiator Instantiator(*this, TemplateArgs, SourceLocation(),
                                    DeclarationName());
  return Instantiator.TransformTemplateArgument(Arg);
}