RFC (C only): [[gnu::allow_vla]] attribute to suppress -Wvla on a single declaration

[Yair Lenga]

Florian,

Thanks for your suggestion. I'm already using macros, but that results
in code that does not look like "C" any more. New "C" developers that
are looking at hte code that uses DECLARE_VLA (or similar) macro -
have trouble understanding this new construct, how to use it,
limitations, etc (e.g., OK to use in `for (DECLARE_VLA(...) ; ; )`.
The attribute provide "in-langauge" support for the same functionality
in a way that is consistent with [[fallthru]], and similar.

Yair

On Thu, Feb 26, 2026 at 6:49 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Yair Lenga via Gcc:
>
> > Hi Martin,
> >
> > Yes - I believe something more "lightweight" than #pragma is needed.
> > What I've observed is that it's very "cumbersome", to write
> >
> > #pragma GCC diagnostic push
> > #pragma GCC diagnostic ignored "-Wvla"
> >      double a[len] ;
> > #pragma GCC diagnostic push
> >
> > Technically, can be "compacted" via #define - but then it's becoming
> > something that it's not "C" any more: e .g.
> > int foo(int how_many) {
> >     DECLARE_VLA(ddd, double, how_many) ;      // Compact but NOT C
> >     int x = 5 ;
> > }
>
> Could you achieve this effect if you used _Pragma?  It can be part of
> macros.  The quoting is a bit tricky to get right, though.  In your
> case, that should be less of an issue because the pragma contents is not
> dependent on macro arguments.
>
> Thanks,
> Florian
>