[Sema] Diagnose template alias declaration in local class

[erik.pilkington]

Summary

Clang currently doesn't diagnose the following invalid code:
void f() {

struct s {
  template<class> using x = int;
};

}

Despite begin rejected by both GCC and the standard, in temp p2. Fixes PR26841.

[rsmith]

test/CXX/temp/temp.decls/temp.mem/p2.cpp

11

Can you add a test for a static data member template too, please?

[erik.pilkington]

Include local static data member template in test. Thanks for taking a look Richard, would you mind committing this for me?

[rsmith]

Landed as r265571.

lib/Sema/SemaDeclCXX.cpp

 
     if (TemplateParamLists.size() != 1) {
       Diag(UsingLoc, diag::err_alias_template_extra_headers)
         << SourceRange(TemplateParamLists[1]->getTemplateLoc(),
          TemplateParamLists[TemplateParamLists.size()-1]->getRAngleLoc());
     }
     TemplateParameterList *TemplateParams = TemplateParamLists[0];
 
+    // Check that we can declare a template here.
+    if (CheckTemplateDeclScope(S, TemplateParams))
+      return nullptr;
+
     // Only consider previous declarations in the same scope.
     FilterLookupForScope(Previous, CurContext, S, /*ConsiderLinkage*/false,
                          /*ExplicitInstantiationOrSpecialization*/false);
     if (!Previous.empty()) {
       Redeclaration = true;
 
       OldDecl = Previous.getAsSingle<TypeAliasTemplateDecl>();
       if (!OldDecl && !Invalid) {

test/CXX/temp/temp.decls/temp.mem/p2.cpp

-// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -std=c++14 -fsyntax-only -verify %s
 
 template <typename>
 void quux();
 
 void fun() {
   struct foo {
     template <typename> struct bar {};  // expected-error{{templates cannot be declared inside of a local class}}
     template <typename> void baz() {}   // expected-error{{templates cannot be declared inside of a local class}}
     template <typename> void qux();     // expected-error{{templates cannot be declared inside of a local class}}
+    template <typename> using corge = int; // expected-error{{templates cannot be declared inside of a local class}}
+    template <typename T> static T grault; // expected-error{{static data member}} expected-error{{templates cannot be declared inside of a local class}}
   };
 }