[clang][parser] Allow GNU-style attributes in enum specifiers

[tbaeder]

Summary

We are parsing both C++11 and GNU-style attributes here, but the previous ProhibitAttributes() call was never working for GNU-style attributes.

GNU-style attributes are however expected to be parsed and not diagnosed, for example in clang/test/Sema/ast-print in the following code:

// CHECK-LABEL: enum __attribute__((deprecated(""))) EnumWithAttributes2 *EnumWithAttributes2Ptr;
// expected-warning@+2 {{'EnumWithAttributes2' is deprecated}}
// expected-note@+1 {{'EnumWithAttributes2' has been explicitly marked deprecated here}}
enum __attribute__((deprecated)) EnumWithAttributes2 *EnumWithAttributes2Ptr;

This is essentially the same as https://reviews.llvm.org/D99278 and needs https://reviews.llvm.org/D97362 to be applied first.

The comment just above this change is a bit confusing since it tries to explain that "an elaborated-type-specifier has a much more constrained grammar", but does not mention any attributes.

[aaron.ballman]

To be clear, this is expected to be an NFC change that allows D97362 to be applied without breaking bots? If so, it'd be helpful to have the changes as part of D97362 because they're critical to that review and so that we get appropriate CI pre-merge testing.

[tbaeder]

Abandoning in favor of https://reviews.llvm.org/D97362

clang/lib/Parse/ParseDecl.cpp

if (TemplateInfo.Kind != ParsedTemplateInfo::NonTemplate &&
     if (TemplateInfo.Kind == ParsedTemplateInfo::ExplicitInstantiation) {
       // Enumerations can't be explicitly instantiated.
       DS.SetTypeSpecError();
       Diag(StartLoc, diag::err_explicit_instantiation_enum);
       return;
     }
 
     assert(TemplateInfo.TemplateParams && "no template parameters");
     TParams = MultiTemplateParamsArg(TemplateInfo.TemplateParams->data(),
                                      TemplateInfo.TemplateParams->size());
   }
 
   if (!Name && TUK != Sema::TUK_Definition) {
     Diag(Tok, diag::err_enumerator_unnamed_no_def);
 
     // Skip the rest of this declarator, up until the comma or semicolon.
     SkipUntil(tok::comma, StopAtSemi);
     return;
   }
 
   // An elaborated-type-specifier has a much more constrained grammar:
   //
   //   'enum' nested-name-specifier[opt] identifier
   //
   // If we parsed any other bits, reject them now.
   //
   // MSVC and (for now at least) Objective-C permit a full enum-specifier
   // or opaque-enum-declaration anywhere.
   if (IsElaboratedTypeSpecifier && !getLangOpts().MicrosoftExt &&
       !getLangOpts().ObjC) {
-    ProhibitAttributes(attrs);
+    ProhibitCXX11Attributes(attrs, diag::err_attributes_not_allowed,
+                            /*DiagnoseEmptyAttrs=*/true);
     if (BaseType.isUsable())
       Diag(BaseRange.getBegin(), diag::ext_enum_base_in_type_specifier)
           << (AllowEnumSpecifier == AllowDefiningTypeSpec::Yes) << BaseRange;
     else if (ScopedEnumKWLoc.isValid())
       Diag(ScopedEnumKWLoc, diag::ext_elaborated_enum_class)
         << FixItHint::CreateRemoval(ScopedEnumKWLoc) << IsScopedUsingClassTag;
   }