[PATCH v7] assert: Support assert as variadic macro for C++26 [PR27276]

[Adhemerval Zanella Netto]

On 03/03/26 09:45, Tomasz Kaminski wrote:
> 
> 
> On Tue, Mar 3, 2026 at 1:39 PM Adhemerval Zanella Netto <adhemerval.zanella@linaro.org <mailto:adhemerval.zanella@linaro.org>> wrote:
> 
> 
> 
>     On 03/03/26 07:56, Yury Khrustalev wrote:
>     > On Wed, Feb 25, 2026 at 03:01:23PM +0100, Tomasz Kamiński wrote:
>     >> From: Jonathan Wakely <jwakely@redhat.com <mailto:jwakely@redhat.com>>
>     >
>     > This patch has a new test that fails to compile with GCC 14.2 (although
>     > it works with GCC 14.3) and causes make check to fail e.g. on Debian 13.
>     >
>     >> ...
>     >>
>     >> diff --git a/assert/test-assert-c++-variadic.cc b/assert/test-assert-c++-variadic.cc
>     >> new file mode 100644
>     >> index 0000000000..1bb8eeb525
>     >> --- /dev/null
>     >>
>     >> ...
>     >>
>     >> +template <typename Ts>
>     >> +constexpr bool
>     >> +assert_works ()
>     >> +{
>     >> +  return requires (Ts ts) {
>     >> +    assert (ts);
>     >> +  };
>     >> +}
>     >> +
>     >> +enum OE { oe };
>     >> +enum TE : int { te };
>     >> +enum class SE : int { se };
>     >> +
>     >> +static_assert ( assert_works <OE> ());
>     >> +static_assert ( assert_works <TE> ());
>     >
>     > These static asserts fail:
>     >
>     >   test-assert-c++-variadic.cc:81:35: error: static assertion failed
>     >      81 | static_assert ( assert_works <OE> ());
>     >       |                 ~~~~~~~~~~~~~~~~~~^~
>     >   test-assert-c++-variadic.cc:82:35: error: static assertion failed
>     >      82 | static_assert ( assert_works <TE> ())
>     >
>     > Also:
>     >
>     >   in ‘constexpr’ expansion of ‘assert_works<OE>()’
>     >   error: ‘constexpr’ call flows off the end of the function
>     >
>     > Looks like
>     >
>     >   #if defined __cplusplus && __cplusplus > 202302L
>     >
>     > is not enough to check if this test is supported or not. XFAIL will not
>     > help here because the test doesn't compile which causes make check to
>     > fail.
> 
>     It does seems to me this is a compiler bug, I checked with gcc version 14.3.1 20250814
>     and gcc version 15.2.1 20260112 without issues.
> 
>     Tomasz, is this a compiler bug or something has changes for gcc 14? If so
>     I think we might need __GNUC_PREREQ for the test.
> 
> Yes, this looks like compiler bug that was fixed in 14.3 and 15, but wasn't able to identify
> the specific change yet. I agree that we need a __GNUC_PREREQ for the snippet
> in question, so around these lines:
> 
> +#if __GNUC_PREREQ (14, 2)

Shouldn't it be __GNUC_PREREQ (14, 3) ?

> template <typename Ts>
> constexpr bool
> assert_works ()
> {
>   return requires (Ts ts) {
>     assert (ts);
>   };
> }
> 
> enum OE { oe };
> enum TE : int { te };
> enum class SE : int { se };
> 
> static_assert ( assert_works <OE> ());
> static_assert ( assert_works <TE> ());
> static_assert (!assert_works <SE> ());
> +#endif 
> 
> Let me know if I should prepare a patch with above change?

Please also add the PR that fixes on a comment for the __GNUC_PREREQ usage.