Re: git: cd0727ec709b - main - libc: Add <stdio.h> C23 feature test macro

> On 15 Aug 2026, at 19:23, Dimitry Andric <dim@FreeBSD.org> wrote:
> 
> On 14 Aug 2026, at 21:32, Faraz Vahedi <kfv@FreeBSD.org> wrote:
>> 
>> The branch main has been updated by kfv:
>> 
>> URL: https://cgit.FreeBSD.org/src/commit/?id=cd0727ec709bb54f8f82104f6113284a15dd3464
>> 
>> commit cd0727ec709bb54f8f82104f6113284a15dd3464
>> Author:     Faraz Vahedi <kfv@FreeBSD.org>
>> AuthorDate: 2026-08-14 12:22:00 +0000
>> Commit:     Faraz Vahedi <kfv@FreeBSD.org>
>> CommitDate: 2026-08-14 19:31:54 +0000
>> 
>>   libc: Add <stdio.h> C23 feature test macro
>> 
>>   Define the __STDC_VERSION_STDIO_H__ feature test macro now that
>>   the header fully conforms to C23.
>> 
>>   Reviewed by:    fuz
>>   Approved by:    fuz (mentor)
>>   MFC after:      1 month
>>   Differential Revision: https://reviews.freebsd.org/D58842
> ...
>> diff --git a/include/stdio.h b/include/stdio.h
>> index ea016d65095d..50e3ff2d1c34 100644
>> --- a/include/stdio.h
>> +++ b/include/stdio.h
>> @@ -32,8 +32,8 @@
>> * SUCH DAMAGE.
>> */
>> 
>> -#ifndef _STDIO_H_
>> -#define _STDIO_H_
>> +#ifndef __STDC_VERSION_STDIO_H__
>> +#define __STDC_VERSION_STDIO_H__ 202311L
>> 
>> #include <sys/cdefs.h>
>> #include <sys/_null.h>
> 
> This particular change appears to have broken the math/gmp port, which
> hasn't functionally changed since 2023.
> 
> It has this construct to detect the existence of FILE:
> 
>  /* For reference, "defined(EOF)" cannot be used here.  In g++ 2.95.4,
>     <iostream> defines EOF but not FILE.  */
>  #if defined (FILE)                                              \
>    || defined (H_STDIO)                                          \
>    || defined (_H_STDIO)               /* AIX */                 \
>    || defined (_STDIO_H)               /* glibc, Sun, SCO */     \
>    || defined (_STDIO_H_)              /* BSD, OSF */            \
>    || defined (__STDIO_H)              /* Borland */             \
>    || defined (__STDIO_H__)            /* IRIX */                \
>    || defined (_STDIO_INCLUDED)        /* HPUX */                \
>    || defined (__dj_include_stdio_h_)  /* DJGPP */               \
>    || defined (_FILE_DEFINED)          /* Microsoft */           \
>    || defined (__STDIO__)              /* Apple MPW MrC */       \
>    || defined (_MSL_STDIO_H)           /* Metrowerks */          \
>    || defined (_STDIO_H_INCLUDED)      /* QNX4 */                \
>    || defined (_ISO_STDIO_ISO_H)       /* Sun C++ */             \
>    || defined (__STDIO_LOADED)         /* VMS */                 \
>    || defined (_STDIO)                 /* HPE NonStop */         \
>    || defined (__DEFINED_FILE)         /* musl */
>  #define _GMP_H_HAVE_FILE 1
>  #endif
> 
> Now that _STDIO_H_ has been removed, the detection fails and another
> part of the port falls over due to an incorrect prototype.
> 
> I guess we could patch the math/gmp port with another
> __STDC_VERSION_STDIO_H__ macro, but it might be good to do an exp-run to
> see if there are more GNU projects which rely on the existence of the
> _STDIO_H_ macro?

FWIW, I would prefer something like this:

diff --git a/include/stdio.h b/include/stdio.h
index 50e3ff2d1c34..07ed71035e84 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -32,8 +32,12 @@
  * SUCH DAMAGE.
  */

+#ifndef _STDIO_H_
+#define _STDIO_H_
+
 #ifndef __STDC_VERSION_STDIO_H__
 #define __STDC_VERSION_STDIO_H__       202311L
+#endif

 #include <sys/cdefs.h>
 #include <sys/_null.h>
@@ -540,4 +544,4 @@ extern int __isthreaded;
 __END_DECLS
 __NULLABILITY_PRAGMA_POP

-#endif /* !__STDC_VERSION_STDIO_H__ */
+#endif /* !_STDIO_H_ */

-Dimitry