[Clang][Parser] Accept GNU attributes preceding C++ style attributes on templates

[eandrews]

Summary

Clang was rejecting valid code where GNU style attributes preceded C++ style attributes in template declarations as follows:

template<int a>
__attribute__((deprecated("oh no!"))) [[deprecated("oh no!")]] void foo();

This PR fixes the bug.

[compnerd]

Could you add a test case for the inverted order of attributes on a template as well? I don't think that there is a test case for that.

[eandrews]

Thanks for the review! I added a couple more tests.

[erichkeane]

This needs a release note, otherwise LGTM!

[eandrews]

Thanks for the review! I've added a release note.

[erichkeane]

1 suggestion, otherwise LGTM.

clang/docs/ReleaseNotes.rst

416 ↗

(On Diff #527406)

[eandrews]

clang/docs/ReleaseNotes.rst

416 ↗

(On Diff #527406)

I'll make this change when I commit the patch. Thanks!

clang/lib/Parse/ParseTemplate.cpp

DeclGroupPtrTy D = ParseCXXClassMemberDeclaration(
         AS, AccessAttrs, TemplateInfo, &DiagsFromTParams);
 
     if (!D || !D.get().isSingleDecl())
       return nullptr;
     return D.get().getSingleDecl();
   }
 
   ParsedAttributes prefixAttrs(AttrFactory);
-  MaybeParseCXX11Attributes(prefixAttrs);
+  ParsedAttributes DeclSpecAttrs(AttrFactory);
+
+  // GNU attributes are applied to the declaration specification while the
+  // standard attributes are applied to the declaration.  We parse the two
+  // attribute sets into different containters so we can apply them during
+  // the regular parsing process.
+  while (MaybeParseCXX11Attributes(prefixAttrs) ||
+         MaybeParseGNUAttributes(DeclSpecAttrs))
+    ;
 
   if (Tok.is(tok::kw_using)) {
     auto usingDeclPtr = ParseUsingDirectiveOrDeclaration(Context, TemplateInfo, DeclEnd,
                                                          prefixAttrs);
     if (!usingDeclPtr || !usingDeclPtr.get().isSingleDecl())
       return nullptr;
     return usingDeclPtr.get().getSingleDecl();
   }
 
   // Parse the declaration specifiers, stealing any diagnostics from
   // the template parameters.
   ParsingDeclSpec DS(*this, &DiagsFromTParams);
+  DS.SetRangeStart(DeclSpecAttrs.Range.getBegin());
+  DS.SetRangeEnd(DeclSpecAttrs.Range.getEnd());
+  DS.takeAttributesFrom(DeclSpecAttrs);
 
   ParseDeclarationSpecifiers(DS, TemplateInfo, AS,
                              getDeclSpecContextFromDeclaratorContext(Context));
 
   if (Tok.is(tok::semi)) {
     ProhibitAttributes(prefixAttrs);
     DeclEnd = ConsumeToken();
     RecordDecl *AnonRecord = nullptr;

clang/test/Parser/attr-order.cpp

 // RUN: %clang_cc1 -fsyntax-only -fms-extensions -Wno-ignored-attributes -verify %s
 
 struct [[]] __attribute__((lockable)) __declspec(dllexport) A {}; // ok
 struct [[]] __declspec(dllexport) __attribute__((lockable)) B {}; // ok
 struct [[]] [[]] __declspec(dllexport) __attribute__((lockable)) C {}; // ok
 struct __declspec(dllexport) [[]] __attribute__((lockable)) D {}; // ok
 struct __declspec(dllexport) __attribute__((lockable)) [[]] E {}; // ok
 struct __attribute__((lockable)) __declspec(dllexport) [[]] F {}; // ok
 struct __attribute__((lockable)) [[]] __declspec(dllexport) G {}; // ok
 struct [[]] __attribute__((lockable)) [[]] __declspec(dllexport) H {}; // ok
 
 [[noreturn]] __attribute__((cdecl)) __declspec(dllexport) void a(); // ok
 [[noreturn]] __declspec(dllexport) __attribute__((cdecl)) void b(); // ok
 [[]] [[noreturn]] __attribute__((cdecl)) __declspec(dllexport) void c(); // ok
 
-// [[]] attributes before a declaration must be at the start of the line.
 __declspec(dllexport) [[noreturn]] __attribute__((cdecl)) void d(); // expected-error {{an attribute list cannot appear here}}
 __declspec(dllexport) __attribute__((cdecl)) [[noreturn]] void e(); // expected-error {{an attribute list cannot appear here}}
 __attribute__((cdecl)) __declspec(dllexport) [[noreturn]] void f(); // expected-error {{an attribute list cannot appear here}}
-__attribute__((cdecl)) [[noreturn]] __declspec(dllexport) void g();
+
+__attribute__((cdecl)) [[noreturn]] __declspec(dllexport) void g(); // ok
 
 [[noreturn]] __attribute__((cdecl))
 [[]]
 __declspec(dllexport) void h();
+
+template <int a>
+__attribute__((cdecl)) [[noreturn]] __declspec(dllexport) void i(); // ok