Implement function template specialization at class scope extension in 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/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: