When parsing a template friend declaration we dropped the template

parameters on the floor in certain cases:
class X {
  template <typename T> friend typename A<T>::Foo;
};

This was parsed as a *non* template friend declaration some how, and
received an ExtWarn. Fixing the parser to actually provide the template
parameters to the freestanding declaration parse triggers the code which
specifically looks for such constructs and hard errors on them.

Along the way, this prevents us from trying to instantiate constructs
like the above inside of a outer template. This is important as loosing
the template parameters means we don't have a well formed declaration
and template instantiation will be unable to rebuild the AST. That fixes
a crash in the GCC test suite.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@130772 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Sema/Sema.h

@@ -1026,10 +1026,11 @@ public:
   void ActOnPopScope(SourceLocation Loc, Scope *S);
   void ActOnTranslationUnitScope(Scope *S);
 
-  /// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
-  /// no declarator (e.g. "struct foo;") is parsed.
   Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
                                    DeclSpec &DS);
+  Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
+                                   DeclSpec &DS,
+                                   MultiTemplateParamsArg TemplateParams);
   
   StmtResult ActOnVlaStmt(const DeclSpec &DS);
 

lib/Parse/ParseDeclCXX.cpp

@@ -1547,7 +1547,7 @@ void Parser::ParseCXXClassMemberDeclaration(AccessSpecifier AS,
   if (Tok.is(tok::semi)) {
     ConsumeToken();
     Decl *TheDecl =
-      Actions.ParsedFreeStandingDeclSpec(getCurScope(), AS, DS);
+      Actions.ParsedFreeStandingDeclSpec(getCurScope(), AS, DS, TemplateParams);
     DS.complete(TheDecl);
     return;
   }

lib/Sema/SemaDecl.cpp

@@ -2132,6 +2132,16 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
 /// no declarator (e.g. "struct foo;") is parsed.
 Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
                                        DeclSpec &DS) {
+  return ParsedFreeStandingDeclSpec(S, AS, DS,
+                                    MultiTemplateParamsArg(*this, 0, 0));
+}
+
+/// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
+/// no declarator (e.g. "struct foo;") is parsed. It also accopts template
+/// parameters to cope with template friend declarations.
+Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
+                                       DeclSpec &DS,
+                                       MultiTemplateParamsArg TemplateParams) {
   Decl *TagD = 0;
   TagDecl *Tag = 0;
   if (DS.getTypeSpecType() == DeclSpec::TST_class ||
@@ -2163,7 +2173,7 @@ Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
     // whatever routines created it handled the friendship aspect.
     if (TagD && !Tag)
       return 0;
-    return ActOnFriendTypeDecl(S, DS, MultiTemplateParamsArg(*this, 0, 0));
+    return ActOnFriendTypeDecl(S, DS, TemplateParams);
   }
 
   // Track whether we warned about the fact that there aren't any

test/CXX/temp/temp.decls/temp.friend/p3.cpp

@@ -8,5 +8,5 @@ class B {
   template <class T> friend class A;
   template <class T> friend class Undeclared;
   
-  template <class T> friend typename A<T>::Member; // expected-warning {{non-class type 'typename A<T>::Member' cannot be a friend}}
+  template <class T> friend typename A<T>::Member; // expected-error {{friend type templates must use an elaborated type}}
 };

test/SemaTemplate/friend-template.cpp

@@ -216,3 +216,11 @@ namespace PR8649 {
 
   X<int, float, 7> x;
 }
+
+// Don't crash, and error on invalid friend type template.
+namespace friend_type_template_no_tag {
+  template <typename T> struct S {
+    template <typename U> friend S<U>; // expected-error{{friend type templates must use an elaborated type}}
+  };
+  template struct S<int>;
+}