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

[Adhemerval Zanella Netto]

On 18/02/26 06:28, Jonathan Wakely wrote:
> On Tue, 17 Feb 2026 at 19:03, Paul Eggert <eggert@cs.ucla.edu> wrote:
>>
>> On 2026-02-17 06:48, Tomasz Kamiński wrote:
>>
>>> On Mon, Feb 16, 2026 at 11:04 PM Paul Eggert <eggert@cs.ucla.edu> wrote:
>>>
>>>>> On 2026-02-09 03:27, Tomasz Kamiński wrote:
>>>>>
>>>>>>> Mainly for testing purposes we allow enabling/disabling variadic assert
>>>>>>> regardless of version of C or C++, by defining __ASSERT_VARIADIC to
>>>>>>> 1/0 respectively before inclusion of <assert>
>>>>>
>>>>> I don't see the need for this extra complexity in this patch. People who
>>>>> want to do that sort of testing can do it in other ways. If there is a
>>>>> need, this part of the patch should be separated out into a different
>>>>> patch.
>>>>>
>>> I would really appreciate guidance on how I could test this in other ways,
>>> in a robust manner.
>>
>> One possibility is that a test case that wants __ASSERT_VARIADIC can do
>> "sed 's/\(define __ASSERT_VARIADIC\) [01]/\1 1/' .../assert.h >assert.h"
>> and then compile the test with "gcc -I.". That's robust enough for a
>> test. But see below.
>>
>>> I was simply considering guarding the content
>>> test-assert-c++-variadic.cc with appropriate __cplusplus value,
>>> but this led to de-facto dead-test.
>>>
>>> The problem I am facing is that the test would need to be compiled with
>>> "-std=c++26", but that is not supported by all versions of GCC that glibc
>>> targets. I have looked into how C23 is tested, to see how to conditionally
>>> pass --std=c23 flag, but they seem to rely on defining ISOC23_SOURCES.
>>
>> I'm a little lost here. It sounds like you're trying to test the C++26
>> features of the new <assert.h> even on C++23 platforms. Why bother? Just
>> test the platform that you have. If it's a "dead-test" that's OK; the
>> feature isn't supported on that platform and need not be tested.
> 
> What is a C++26 platform? There are no platforms where the compiler
> defaults to C++26, and probably won't be for maybe 5 years. So the
> test would be dead until then, on all platforms. A test that never
> runs anywhere is not a good test.
> 
> What's desirable is to enable the test now for platforms where GCC
> supports -std=c++26 as an option, but if the test adds -std=c++26 to
> the makefile then it will fail on platforms where GCC is old and
> _doesn't_ support that option.

We can add a configure check for --std=c++26 and enable the test iff
the C++ compiler supports it.