Re: [PATCH] warnings.m4: provide a means to specify the program to compile

[Jim Meyering]

Akim Demaille wrote:
> I have submitted this patch several times in this thread (starting at
> http://lists.gnu.org/archive/html/bug-gnulib/2012-04/msg00049.html),
> and for some reason it remains unnoticed, and uncommented.  Please let
> me know what is wrong in my approach.
>
> I would like to wrap a Bison 2.5.1 soon, and I expect to use this
> patch to decide whether I enable -Wzero-as-null-pointer-constant (as
> G++ can happily reject 0 as a pointer without supporting nullptr, not
> considered as a bug by G++ people).

Hi Akim,

I was burned by that, too, while trying to build bison using gcc-4.8.x.

> The attached patch enhances warnings.m4 in several ways:
>
> - gl_COMPILER_OPTION_IF allows to define more fine grain tests on the
>   behavior of the compiler.  Forcing the result to be an assignment to
>   a variable (which is AC_SUBST'ed) does not seem to offer the
>   orthogonal design one would expect.  This would be useful elsewhere,
>   for instance in manywarnings, as I have already reported
>   (http://lists.gnu.org/archive/html/bug-gnulib/2012-03/msg00198.html)
>
> - separating the diagnostic part from the action part provides a
>   cleaner way to implement test cases.
>
> - separating the diagnostic part from the action part helps extending
>   both in a cleaner way:
>
>   - it allowed me to cleanly integrate the missing AC_SUBST for
>     WARN_CFLAGS instead of leaving this to modules/warnings
>
>   - it will make it easier to check for the answers of the compiler on
>     stderr (as currently, we merely check whether the compiler rejects
>     the candidate option with an error status; this results in uselessly
>     long compilation command lines, and spurious warnings in some
>     situations).
>
> - the added parameter to gl_WARN_ADD allows to fine tune whether a
>   given warning is wanted or not (e.g., 0 vs. nullptr as above).

I like the patch.
If no one objects, I'll push it later today.