Re: Getting AC_PROG_CC_C99

[Gary V. Vaughan]

[Re-adding bug-autoconf]

Hi Bruno,

On 30 Sep 2011, at 16:56, Bruno Haible wrote:
> Gary V. Vaughan wrote:
>> But why emit a warning when
>> we can just fix-up the definition on the fly? ...
>> This changeset fixes AC_PROG_CC_C99
>> (and effectively AC_PROG_CC_STDC) whether it is called before or
>> after gl_EARLY, directly or by AC_PROG_CC_STDC, or even not at all!
>> ...
>> +[AC_PROVIDE_IFELSE([AC_PROG_CC_C99],
>> +        [AC_DEFUN([AC_PROG_CC_C99])],
>> +  [AC_DEFUN([AC_PROG_CC_C99],
>> +    m4_defn([AC_PROG_CC_C99])[AC_DEFUN([AC_PROG_CC_C99])])])])
> 
> We can't use this. AC_PROVIDE_IFELSE is undocumented.

Oh yuck.  Good point.  Libtool is a bad citizen... oopsie.

>> By putting the fix in gl_EARLY rather than autoconf itself, there's
>> still the possibility of getting multiple expansions with something
>> like:
>> 
>>  AC_PROG_CC
>>  AC_PROG_CC_C99
>>  AC_PROG_CC_STDC
>>  gl_EARLY
>> 
>> But that seems pathological to me in any case, so I haven't tried to
>> address that.
> 
> That's why I think it should be addressed in Autoconf.

And I think it is as easy as adding AC_DEFUN([AC_PROG_CC_C99]) to the
end of the existing AC_PROG_CC_C99 macro to make sure subsequent invocations
expand to nothing.  And maybe the same thing in AC_PROG_CC_C89 if it has the
same bug.

Autoconf folks, please ask me if you'd like a patch to that effect.

>> * m4/gnulib-common (gl_PROG_CC_C99_ONCE): New macro to automatically
>> neuter AC_PROG_CC_C99 after first invocation.
> 
> We didn't say that we want to enable C99 for all programs. See
> <http://lists.gnu.org/archive/html/bug-gnulib/2011-09/msg00441.html>

Ah yes, I got a bit too excited there.

> I'm applying this for now. Maybe you have a more acceptable workaround against
> the "$CC gets augmented twice" problem?

Your patch is perfectly acceptable to me already.  Thank you!

> 2011-09-30  Bruno Haible  <address@hidden>
> 
>       Centralize C99 requirement.
>       * m4/gnulib-common.m4 (gl_PROG_CC_C99): New macro.
>       * modules/stdarg (configure.ac-early): Invoke it instead of
>       AC_PROG_CC_STDC.
>       Reported by Gary V. Vaughan and Paul Eggert.

Cheers,
-- 
Gary V. Vaughan (gary AT gnu DOT org)