[Concepts] Add diagnostic: non template declaration

[nwilson]

Summary

Adding diagnostic for concepts declared as non template (function or variable)

[hubert.reinterpretcast]

include/clang/Basic/DiagnosticSemaKinds.td

1970

Using just "concept" here to refer to the specifier is a bit confusing. Perhaps:
"the concept specifier may only be applied to the definition of a function or variable template"

[nwilson]

modifying diagnostic message to: 'concept' can only appear on the definition of a function template or variable template

[hubert.reinterpretcast]

In test/Parser/cxx-concept-declaration.cpp:

concept D1 = true; // expected-error {{C++ requires a type specifier for all declarations}}

triggers the new error and fails the test.

[rsmith]

LGTM

[nwilson]

Thanks Richard.

Sorry about the failed test that Hubert brought up. I'll remove that if no
one objects since it's covered by the Sema tests in this Patch.

Potentially that test in the Parser could be modified to be:
template<typename T>
concept D1 = true;

However, it will just pass and I believe it needs a diagnostic for the
return type not being bool.

[nwilson]

Removing failing test case (in Parser) created by this Patch

include/clang/Basic/DiagnosticSemaKinds.td

def note_non_literal_nontrivial_dtor : Note<
   "%0 is not literal because it has a non-trivial destructor">;
 def warn_private_extern : Warning<
   "use of __private_extern__ on a declaration may not produce external symbol "
   "private to the linkage unit and is deprecated">, InGroup<PrivateExtern>;
 def note_private_extern : Note<
   "use __attribute__((visibility(\"hidden\"))) attribute instead">;
 
 // C++ Concepts TS
+def err_concept_decl_non_template : Error<
+  "'concept' can only appear on the definition of a function template or variable template">;
 def err_concept_decls_may_only_appear_in_namespace_scope : Error<
   "concept declarations may only appear in namespace scope">;
 def err_function_concept_not_defined : Error<
   "function concept declaration must be a definition">;
 
 // C++11 char16_t/char32_t
 def warn_cxx98_compat_unicode_type : Warning<
   "'%0' type specifier is incompatible with C++98">,

lib/Sema/SemaDecl.cpp

NamedDecl *Sema::HandleDeclarator(Scope *S, Declarator &D,
   // of a function declaration (C++ only).
   if (getLangOpts().CPlusPlus)
     CheckExtraCXXDefaultArguments(D);
 
   if (D.getDeclSpec().isConceptSpecified()) {
     // C++ Concepts TS [dcl.spec.concept]p1: The concept specifier shall be
     // applied only to the definition of a function template or variable
     // template, declared in namespace scope
+    if (!TemplateParamLists.size()) {
+      Diag(D.getDeclSpec().getConceptSpecLoc(),
+           diag::err_concept_decl_non_template);
+      return nullptr;
+    }
+
     if (!DC->getRedeclContext()->isFileContext()) {
       Diag(D.getIdentifierLoc(),
            diag::err_concept_decls_may_only_appear_in_namespace_scope);
       return nullptr;
     }
   }
 
   NamedDecl *New;

test/SemaCXX/cxx-concept-declaration.cpp

 
 struct B {
   template<typename T> concept bool D2() { return true; } // expected-error {{concept declarations may only appear in namespace scope}}
 };
 
 struct C {
   template<typename T> static concept bool D3 = true; // expected-error {{concept declarations may only appear in namespace scope}}
 };
+
+concept bool D4() { return true; } // expected-error {{'concept' can only appear on the definition of a function template or variable template}}
+
+concept bool D5 = true; // expected-error {{'concept' can only appear on the definition of a function template or variable template}}