[PATCH] Disallowing just GNU-style attributes in certain positions

[Richard Smith]

On Thu, Jul 17, 2014 at 11:36 AM, Aaron Ballman <aaron at aaronballman.com>
wrote:

> GNU-style type attributes are not allowed in new expressions, such as:
>
> auto *P = new int * __attribute__((attr));
>
> We silently accept them in clang, but have a FIXME in the code to
> address the issue. This patch is an initial stab at addressing the
> issue, and I am looking for feedback on whether my approach is
> reasonable or not. (It disables support for GNU attributes, but not
> other vendor attributes which should remain supported.)
>
> Note, the attached test case does not currently pass. It only checks
> for one error diagnostic, but the actual diagnostics for that code
> are:
>
> ..\llvm\tools\clang\test\SemaCXX\attr-gnu.cpp:4:22: error: an
> attribute list cannot appear here
>   auto P = new int * __attribute__((vector_size(8))); // expected-error ...
>                      ^
> ..\llvm\tools\clang\test\SemaCXX\attr-gnu.cpp:4:21: error: expected
> ';' at end of declaration
>   auto P = new int * __attribute__((vector_size(8))); // expected-error ...
>                     ^
>                     ;
> ..\llvm\tools\clang\test\SemaCXX\attr-gnu.cpp:4:22: warning:
> declaration does not declare anything [-Wmissing-declarations]
>   auto P = new int * __attribute__((vector_size(8))); // expected-error ...
>                      ^~~~~~~~~~~~~
> 1 warning and 2 errors generated.
>
> The first diagnostic is obviously correct, but are the other two
> reasonable diagnostics as well?
>

I would prefer for them to be suppressed: if you're in the
GNUAttributesProhibited case and you see a GNU attribute, I think you
should both parse it and diagnose it.

If the approach is reasonable, I'll clean the patch up, add more test
> cases, etc. I mostly wanted to check my direction first. Thanks!
>

The direction looks good to me. I think your AttrRequirements enum could be
made clearer (separate XAllowed and XProhibited flags seem a bit confusing
at first -- perhaps XParsed and XParsedAndRejected or something along those
lines might be clearer?)
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