bug#31347: AM_PROG_CC_C_O is disabled by gnulib std-gnu11.m4

[Jamal Natour]

Hi,

As a user of C++11 and C++14, I use the ax_cxx_compile_stdcxx variants,
these have seemed to work on the various combinations of
platforms/compilers I've used.

https://github.com/jamal-fuma/fuma_m4/blob/master/ax_cxx_compile_stdcxx.m4
https://github.com/jamal-fuma/fuma_m4/blob/master/ax_cxx_compile_stdcxx_14.m4

Perhaps these will offer a workaround until such time as you can solve
the issue.

HTH

Jamal

On 15:56 Wed 02 May 2018    , Mike Miller wrote:
> Hi,
>
> In GNU Octave, we are embracing a lot of C++11, and so we are using the
> gnulib std-gnu11.m4 drop-in to ensure that the compiler conforms to the
> latest standards. I think several other GNU projects also use this file.
>
> The std-gnu11.m4 file defines AC_PROG_CC and AC_PROG_CXX replacements,
> which I think are backported from Autoconf git.
>
> In a trivial project, for example
>
>     AC_INIT([test], [0])
>     AM_INIT_AUTOMAKE([1.14 foreign])
>     AC_PROG_CC
>     AC_CONFIG_FILES([Makefile])
>     AC_OUTPUT
>
> the AM_PROG_CC_C_O feature test is automatically called, as expected and
> described in the Automake 1.14 NEWS.
>
> With std-gnu11.m4 added to this project, however, the AM_PROG_CC_C_O
> macro is no longer called, either automatically or manually. The
> intention of Automake to ensure that this test is always done is
> defeated simply by including this file.
>
> If a call to the real macro
>
>     _AM_PROG_CC_C_O
>
> is added after AC_PROG_CC, then the feature test is restored.
>
> I know enough m4 to get by, but I suspect this has to do with the order
> of inclusion, and that Automake redefines AC_PROG_CC to call its own
> _AM_PROG_CC_C_O, which is later clobbered by the inclusion of
> std-gnu11.m4.
>
> Is there anything Automake can do to ensure that AM_PROG_CC_C_O is
> called even if AC_PROG_CC is redefined locally?
>
> Even if you judge this not to be an Automake bug, I wanted to bring this
> to your attention, since the std-gnu11.m4 file is the recommended way to
> rely on modern language standards support at the moment.
>
> Thanks,
>
> --
> mike



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