[PATCH] D141177: [Clang] Don't tell people to place _Alignas on a struct in diagnostics

[Aaron Ballman via Phabricator via cfe-commits]

aaron.ballman added inline comments.


================
Comment at: clang/lib/Sema/SemaDecl.cpp:5337-5346
+      if (AL.isC11AlignasAttribute()) {
+        // Don't use the message with placement with _Alignas.
+        // This is because C doesnt let you use _Alignas on type declarations.
+        Diag(AL.getLoc(), diag::warn_attribute_ignored) << AL;
+      } else {
+        Diag(AL.getLoc(), AL.isRegularKeywordAttribute()
+                              ? diag::err_declspec_keyword_has_no_effect
----------------
I think this might be a bit more clear:
```
unsigned DiagID;
if (AL.isC11AlignasAttribute()) {
  // Don't use the message with placement with _Alignas.
  // This is because C doesnt let you use _Alignas on type declarations.
  DiagID = diag::warn_attribute_ignored;
} else if (AL.isRegularKeywordAttribute())
  DiagID = diag::err_declspec_keyword_has_no_effect;
else
  DiagID = diag::warn_declspec_attribute_ignored;

Diag(AL.getLoc(), DiagID) << AL << GetDiagnosticTypeSpecifierID(DS);
```


================
Comment at: clang/test/Parser/c1x-alignas.c:12
 
+_Alignas(int) struct c6; // expected-warning {{'_Alignas' attribute ignored}}
+
----------------
I'd like to see a C23-specific test that does:
```
alignas(int) struct c7;
```
(the test doesn't have to be in this file, but it's to validate that we correctly handle `alignas` when it's a keyword that aliases to `_Alignas`.)


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D141177/new/

https://reviews.llvm.org/D141177