Implement function template specialization at class scope extension i…

…n Microsoft mode. A new AST node is introduced: ClassScopeFunctionSpecialization. This node holds a FunctionDecl that is not yet specialized; then during the class template instantiation the ClassScopeFunctionSpecialization will spawn the actual function specialization.

Example:
template <class T>
class A {
public:
  template <class U> void f(U p) {  }
  template <> void f(int p) {  } // <== class scope specialization
};

This extension is necessary to parse MSVC standard C++ headers, MFC and ATL code.
BTW, with this feature in, clang can parse (-fsyntax-only) all the MSVC 2010 standard header files without any error.

llvm-svn: 137573

clang/include/clang/AST/ASTContext.h

@@ -152,6 +152,11 @@ class ASTContext : public llvm::RefCountedBase<ASTContext> {
   /// \brief Mapping from __block VarDecls to their copy initialization expr.
   llvm::DenseMap<const VarDecl*, Expr*> BlockVarCopyInits;
 
+  /// \brief Mapping from class scope functions specialization to their
+  ///  templateS pattern.
+  llvm::DenseMap<const FunctionDecl*, FunctionDecl*>
+    ClassScopeSpecilizationPattern;
+
   /// \brief Representation of a "canonical" template template parameter that
   /// is used in canonical template names.
   class CanonicalTemplateTemplateParm : public llvm::FoldingSetNode {
@@ -382,6 +387,11 @@ class ASTContext : public llvm::RefCountedBase<ASTContext> {
   MemberSpecializationInfo *getInstantiatedFromStaticDataMember(
                                                            const VarDecl *Var);
 
+  FunctionDecl *getClassScopeSpecializationPattern(const FunctionDecl *FD);
+
+  void setClassScopeSpecializationPattern(FunctionDecl *FD,
+                                          FunctionDecl *Pattern);
+
   /// \brief Note that the static data member \p Inst is an instantiation of
   /// the static data member template \p Tmpl of a class template.
   void setInstantiatedFromStaticDataMember(VarDecl *Inst, VarDecl *Tmpl,

clang/include/clang/AST/Decl.h

@@ -1851,7 +1851,11 @@ class FunctionDecl : public DeclaratorDecl, public DeclContext,
   bool isFunctionTemplateSpecialization() const {
     return getPrimaryTemplate() != 0;
   }
-
+
+  /// \brief Retrieve the class scope template pattern that this function
+  ///  template specialization is instantiated from.
+  FunctionDecl *getClassScopeSpecializationPattern() const;
+
   /// \brief If this function is actually a function template specialization,
   /// retrieve information about this function template specialization. 
   /// Otherwise, returns NULL.

clang/include/clang/AST/DeclTemplate.h

@@ -2097,6 +2097,58 @@ class TypeAliasTemplateDecl : public RedeclarableTemplateDecl,
   friend class ASTDeclWriter;
 };
 
+/// Declaration of a function specialization at template class scope.
+/// This is a non standard extension needed to support MSVC.
+/// For example:
+/// template <class T>
+/// class A {
+///    template <class U> void foo(U a) { }
+///    template<> void foo(int a) { }
+/// }
+///
+/// "template<> foo(int a)" will be saved in Specialization as a normal
+/// CXXMethodDecl. Then during an instantiation of class A, it will be
+/// transformed into an actual function specialization.
+class ClassScopeFunctionSpecializationDecl : public Decl {
+private:
+  ClassScopeFunctionSpecializationDecl(DeclContext *DC, SourceLocation Loc,
+                                       CXXMethodDecl *FD)
+    : Decl(Decl::ClassScopeFunctionSpecialization, DC, Loc),
+      Specialization(FD) {}
+
+  ClassScopeFunctionSpecializationDecl(EmptyShell Empty)
+    : Decl(Decl::ClassScopeFunctionSpecialization, Empty) {}
+
+  CXXMethodDecl *Specialization;
+
+public:
+  CXXMethodDecl *getSpecialization() const { return Specialization; }
+
+  static ClassScopeFunctionSpecializationDecl *Create(ASTContext &C,
+                                                      DeclContext *DC,
+                                                      SourceLocation Loc,
+                                                      CXXMethodDecl *FD) {
+    return new (C) ClassScopeFunctionSpecializationDecl(DC , Loc, FD);
+  }
+
+  static ClassScopeFunctionSpecializationDecl *Create(ASTContext &Context,
+                                                      EmptyShell Empty) {
+    return new (Context)ClassScopeFunctionSpecializationDecl(0,
+                                                         SourceLocation(), 0);
+  }
+  // Implement isa/cast/dyncast/etc.
+  static bool classof(const Decl *D) { return classofKind(D->getKind()); }
+  static bool classofKind(Kind K) {
+    return K == Decl::ClassScopeFunctionSpecialization;
+  }
+  static bool classof(const ClassScopeFunctionSpecializationDecl *D) {
+    return true;
+  }
+
+  friend class ASTDeclReader;
+  friend class ASTDeclWriter;
+};
+
 /// Implementation of inline functions that require the template declarations
 inline AnyFunctionDecl::AnyFunctionDecl(FunctionTemplateDecl *FTD)
   : Function(FTD) { }

clang/include/clang/AST/RecursiveASTVisitor.h

@@ -1114,6 +1114,10 @@ DEF_TRAVERSE_DECL(FriendTemplateDecl, {
     }
   })
 
+DEF_TRAVERSE_DECL(ClassScopeFunctionSpecializationDecl, {
+  TRY_TO(TraverseDecl(D->getSpecialization()));
+ })
+
 DEF_TRAVERSE_DECL(LinkageSpecDecl, { })
 
 DEF_TRAVERSE_DECL(ObjCClassDecl, {

clang/include/clang/Basic/DeclNodes.td

@@ -74,3 +74,4 @@ def Friend : Decl;
 def FriendTemplate : Decl;
 def StaticAssert : Decl;
 def Block : Decl, DeclContext;
+def ClassScopeFunctionSpecialization : Decl;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -2028,6 +2028,9 @@ def err_not_class_template_specialization : Error<
   "parameter}0">;
 def err_function_specialization_in_class : Error<
   "cannot specialize a function %0 within class scope">;
+def ext_function_specialization_in_class : ExtWarn<
+  "explicit specialization of %0 within class scope in a Microsoft extension">,
+  InGroup<Microsoft>;
 def ext_explicit_specialization_storage_class : ExtWarn<
   "explicit specialization cannot have a storage class">;
 def err_explicit_specialization_inconsistent_storage_class : Error<

clang/include/clang/Sema/Sema.h

@@ -1002,7 +1002,8 @@ class Sema {
                                      LookupResult &Previous,
                                      MultiTemplateParamsArg TemplateParamLists,
                                      bool IsFunctionDefinition,
-                                     bool &Redeclaration);
+                                     bool &Redeclaration,
+                                     bool &AddToScope);
   bool AddOverriddenMethods(CXXRecordDecl *DC, CXXMethodDecl *MD);
   void DiagnoseHiddenVirtualMethods(CXXRecordDecl *DC, CXXMethodDecl *MD);
   void CheckFunctionDeclaration(Scope *S,

clang/include/clang/Sema/Template.h

@@ -350,7 +350,8 @@ namespace clang {
                             TemplateParameterList *TemplateParams = 0);
     Decl *VisitCXXRecordDecl(CXXRecordDecl *D);
     Decl *VisitCXXMethodDecl(CXXMethodDecl *D,
-                             TemplateParameterList *TemplateParams = 0);
+                             TemplateParameterList *TemplateParams = 0,
+                             bool IsClassScopeSpecialization = false);
     Decl *VisitCXXConstructorDecl(CXXConstructorDecl *D);
     Decl *VisitCXXDestructorDecl(CXXDestructorDecl *D);
     Decl *VisitCXXConversionDecl(CXXConversionDecl *D);
@@ -367,6 +368,8 @@ namespace clang {
     Decl *VisitUsingShadowDecl(UsingShadowDecl *D);
     Decl *VisitUnresolvedUsingValueDecl(UnresolvedUsingValueDecl *D);
     Decl *VisitUnresolvedUsingTypenameDecl(UnresolvedUsingTypenameDecl *D);
+    Decl *VisitClassScopeFunctionSpecializationDecl(
+                                      ClassScopeFunctionSpecializationDecl *D);
 
     // Base case. FIXME: Remove once we can instantiate everything.
     Decl *VisitDecl(Decl *D) {

clang/include/clang/Serialization/ASTBitCodes.h

@@ -826,7 +826,10 @@ namespace clang {
       DECL_INDIRECTFIELD,
       /// \brief A NonTypeTemplateParmDecl record that stores an expanded
       /// non-type template parameter pack.
-      DECL_EXPANDED_NON_TYPE_TEMPLATE_PARM_PACK
+      DECL_EXPANDED_NON_TYPE_TEMPLATE_PARM_PACK,
+      /// \brief A ClassScopeFunctionSpecializationDecl record a class scope
+      /// function specialization. (Microsoft extension).
+      DECL_CLASS_SCOPE_FUNCTION_SPECIALIZATION
     };
 
     /// \brief Record codes for each kind of statement or expression.

clang/lib/AST/ASTContext.cpp

@@ -518,6 +518,24 @@ ASTContext::setInstantiatedFromStaticDataMember(VarDecl *Inst, VarDecl *Tmpl,
     = new (*this) MemberSpecializationInfo(Tmpl, TSK, PointOfInstantiation);
 }
 
+FunctionDecl *ASTContext::getClassScopeSpecializationPattern(
+                                                     const FunctionDecl *FD){
+  assert(FD && "Specialization is 0");
+  llvm::DenseMap<const FunctionDecl*, FunctionDecl *>::const_iterator Pos
+    = ClassScopeSpecilizationPattern.find(FD);
+  if (Pos == ClassScopeSpecilizationPattern.end())
+    return 0;
+
+  return Pos->second;
+}
+
+void ASTContext::setClassScopeSpecializationPattern(FunctionDecl *FD,
+                                        FunctionDecl *Pattern) {
+  assert(FD && "Specialization is 0");
+  assert(Pattern && "Class scope specialization pattern is 0");
+  ClassScopeSpecilizationPattern[FD] = Pattern;
+}
+
 NamedDecl *
 ASTContext::getInstantiatedFromUsingDecl(UsingDecl *UUD) {
   llvm::DenseMap<UsingDecl *, NamedDecl *>::const_iterator Pos
@@ -6439,5 +6457,6 @@ size_t ASTContext::getSideTableAllocatedMemory() const {
     + llvm::capacity_in_bytes(InstantiatedFromUnnamedFieldDecl)
     + llvm::capacity_in_bytes(OverriddenMethods)
     + llvm::capacity_in_bytes(Types)
-    + llvm::capacity_in_bytes(VariableArrayTypes);
+    + llvm::capacity_in_bytes(VariableArrayTypes)
+    + llvm::capacity_in_bytes(ClassScopeSpecilizationPattern);
 }

clang/lib/AST/Decl.cpp

@@ -1922,13 +1922,17 @@ bool FunctionDecl::isImplicitlyInstantiable() const {
 
   switch (getTemplateSpecializationKind()) {
   case TSK_Undeclared:
-  case TSK_ExplicitSpecialization:
   case TSK_ExplicitInstantiationDefinition:
     return false;
 
   case TSK_ImplicitInstantiation:
     return true;
 
+  // It is possible to instantiate TSK_ExplicitSpecialization kind
+  // if the FunctionDecl has a class scope specialization pattern.
+  case TSK_ExplicitSpecialization:
+    return getClassScopeSpecializationPattern() != 0;
+
   case TSK_ExplicitInstantiationDeclaration:
     // Handled below.
     break;
@@ -1951,6 +1955,10 @@ bool FunctionDecl::isImplicitlyInstantiable() const {
 }                      
 
 FunctionDecl *FunctionDecl::getTemplateInstantiationPattern() const {
+  // Handle class scope explicit specialization special case.
+  if (getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
+    return getClassScopeSpecializationPattern();
+
   if (FunctionTemplateDecl *Primary = getPrimaryTemplate()) {
     while (Primary->getInstantiatedFromMemberTemplate()) {
       // If we have hit a point where the user provided a specialization of
@@ -1976,6 +1984,10 @@ FunctionTemplateDecl *FunctionDecl::getPrimaryTemplate() const {
   return 0;
 }
 
+FunctionDecl *FunctionDecl::getClassScopeSpecializationPattern() const {
+    return getASTContext().getClassScopeSpecializationPattern(this);
+}
+
 const TemplateArgumentList *
 FunctionDecl::getTemplateSpecializationArgs() const {
   if (FunctionTemplateSpecializationInfo *Info

clang/lib/AST/DeclBase.cpp

@@ -493,6 +493,7 @@ unsigned Decl::getIdentifierNamespaceForKind(Kind DeclKind) {
     case UsingDirective:
     case ClassTemplateSpecialization:
     case ClassTemplatePartialSpecialization:
+    case ClassScopeFunctionSpecialization:
     case ObjCImplementation:
     case ObjCCategory:
     case ObjCCategoryImpl:

clang/lib/CodeGen/CGDecl.cpp

@@ -70,6 +70,7 @@ void CodeGenFunction::EmitDecl(const Decl &D) {
   case Decl::Friend:
   case Decl::FriendTemplate:
   case Decl::Block:
+  case Decl::ClassScopeFunctionSpecialization:
     assert(0 && "Declaration should not be in declstmts!");
   case Decl::Function:  // void X();
   case Decl::Record:    // struct/union/class X;

clang/lib/Sema/SemaDecl.cpp

@@ -1722,9 +1722,16 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD) {
       // Preserve triviality.
       NewMethod->setTrivial(OldMethod->isTrivial());
 
+      // MSVC allows explicit template specialization at class scope:
+      // 2 CXMethodDecls referring to the same function will be injected.
+      // We don't want a redeclartion error.
+      bool IsClassScopeExplicitSpecialization =
+                              OldMethod->isFunctionTemplateSpecialization() &&
+                              NewMethod->isFunctionTemplateSpecialization();
       bool isFriend = NewMethod->getFriendObjectKind();
 
-      if (!isFriend && NewMethod->getLexicalDeclContext()->isRecord()) {
+      if (!isFriend && NewMethod->getLexicalDeclContext()->isRecord() &&
+          !IsClassScopeExplicitSpecialization) {
         //    -- Member function declarations with the same name and the
         //       same parameter types cannot be overloaded if any of them
         //       is a static member function declaration.
@@ -3226,6 +3233,7 @@ Decl *Sema::HandleDeclarator(Scope *S, Declarator &D,
     Previous.clear();
 
   bool Redeclaration = false;
+  bool AddToScope = true;
   if (D.getDeclSpec().getStorageClassSpec() == DeclSpec::SCS_typedef) {
     if (TemplateParamLists.size()) {
       Diag(D.getIdentifierLoc(), diag::err_template_typedef);
@@ -3236,7 +3244,8 @@ Decl *Sema::HandleDeclarator(Scope *S, Declarator &D,
   } else if (R->isFunctionType()) {
     New = ActOnFunctionDeclarator(S, D, DC, R, TInfo, Previous,
                                   move(TemplateParamLists),
-                                  IsFunctionDefinition, Redeclaration);
+                                  IsFunctionDefinition, Redeclaration,
+                                  AddToScope);
   } else {
     New = ActOnVariableDeclarator(S, D, DC, R, TInfo, Previous,
                                   move(TemplateParamLists),
@@ -3248,7 +3257,8 @@ Decl *Sema::HandleDeclarator(Scope *S, Declarator &D,
 
   // If this has an identifier and is not an invalid redeclaration or 
   // function template specialization, add it to the scope stack.
-  if (New->getDeclName() && !(Redeclaration && New->isInvalidDecl()))
+  if (New->getDeclName() && AddToScope &&
+       !(Redeclaration && New->isInvalidDecl()))
     PushOnScopeChains(New, S);
 
   return New;
@@ -4201,7 +4211,8 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
                               QualType R, TypeSourceInfo *TInfo,
                               LookupResult &Previous,
                               MultiTemplateParamsArg TemplateParamLists,
-                              bool IsFunctionDefinition, bool &Redeclaration) {
+                              bool IsFunctionDefinition, bool &Redeclaration,
+                              bool &AddToScope) {
   assert(R.getTypePtr()->isFunctionType());
 
   // TODO: consider using NameInfo for diagnostic.
@@ -4266,6 +4277,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
   FunctionTemplateDecl *FunctionTemplate = 0;
   bool isExplicitSpecialization = false;
   bool isFunctionTemplateSpecialization = false;
+  bool isDependentClassScopeExplicitSpecialization = false;
 
   if (!getLangOptions().CPlusPlus) {
     // Determine whether the function was written with a
@@ -4769,10 +4781,11 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     } else if (isFunctionTemplateSpecialization) {
       if (CurContext->isDependentContext() && CurContext->isRecord() 
           && !isFriend) {
-        Diag(NewFD->getLocation(), diag::err_function_specialization_in_class)
+        isDependentClassScopeExplicitSpecialization = true;
+        Diag(NewFD->getLocation(), getLangOptions().Microsoft ? 
+          diag::ext_function_specialization_in_class :
+          diag::err_function_specialization_in_class)
           << NewFD->getDeclName();
-        NewFD->setInvalidDecl();
-        return 0;
       } else if (CheckFunctionTemplateSpecialization(NewFD,
                                   (HasExplicitTemplateArgs ? &TemplateArgs : 0),
                                                      Previous))
@@ -4802,8 +4815,9 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
     }
 
     // Perform semantic checking on the function declaration.
-    CheckFunctionDeclaration(S, NewFD, Previous, isExplicitSpecialization,
-                             Redeclaration);
+    if (!isDependentClassScopeExplicitSpecialization)
+      CheckFunctionDeclaration(S, NewFD, Previous, isExplicitSpecialization,
+                               Redeclaration);
 
     assert((NewFD->isInvalidDecl() || !Redeclaration ||
             Previous.getResultKind() != LookupResult::FoundOverloaded) &&
@@ -4984,6 +4998,18 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
           Context.setcudaConfigureCallDecl(NewFD);
         }
       }
+
+  // Here we have an function template explicit specialization at class scope.
+  // The actually specialization will be postponed to template instatiation
+  // time via the ClassScopeFunctionSpecializationDecl node.
+  if (isDependentClassScopeExplicitSpecialization) {
+    ClassScopeFunctionSpecializationDecl *NewSpec =
+                         ClassScopeFunctionSpecializationDecl::Create(
+                                Context, CurContext,  SourceLocation(), 
+                                cast<CXXMethodDecl>(NewFD));
+    CurContext->addDecl(NewSpec);
+    AddToScope = false;
+  }
 
   return NewFD;
 }

clang/lib/Sema/SemaDeclCXX.cpp

@@ -8652,10 +8652,11 @@ Decl *Sema::ActOnFriendFunctionDecl(Scope *S, Declarator &D, bool IsDefinition,
   }
 
   bool Redeclaration = false;
+  bool AddToScope = true;
   NamedDecl *ND = ActOnFunctionDeclarator(DCScope, D, DC, T, TInfo, Previous,
                                           move(TemplateParams),
                                           IsDefinition,
-                                          Redeclaration);
+                                          Redeclaration, AddToScope);
   if (!ND) return 0;
 
   assert(ND->getDeclContext() == DC);

clang/lib/Sema/SemaTemplate.cpp

@@ -4511,9 +4511,18 @@ static bool CheckTemplateSpecializationScope(Sema &S,
   }
 
   if (S.CurContext->isRecord() && !IsPartialSpecialization) {
-    S.Diag(Loc, diag::err_template_spec_decl_class_scope)
-      << Specialized;
-    return true;
+    if (S.getLangOptions().Microsoft) {
+      // Do not warn for class scope explicit specialization during
+      // instantiation, warning was already emitted during pattern
+      // semantic analysis.
+      if (!S.ActiveTemplateInstantiations.size())
+        S.Diag(Loc, diag::ext_function_specialization_in_class)
+          << Specialized;
+    } else {
+      S.Diag(Loc, diag::err_template_spec_decl_class_scope)
+        << Specialized;
+      return true;
+    }
   }
 
   // C++ [temp.class.spec]p6: