Re: Support AX_CXX_COMPILE_STDCXX_11 macro in autoconf

Keith Marshall <[email protected]> Sat, 18 Jan 2020 22:18:00 +0000
Newsgroups	gmane.comp.gnu.mingw.user
Organization	MinGW.org Project
Message-ID	<[email protected]>
On 18/01/2020 21:33, Anton Shepelev wrote:
> I had a warning about another macro:
> 
>    configure.ac:215: warning: macro `AM_PATH_ALSA' not found in library
> 
> which is indeed missing from my system,

The "AM_" namespace belongs to automake; automake knows this, and marks
it as a reserved namespace, so will issue diagnostics for unexpanded
macros within it.

> but it said nothing about AX_CXX_COMPILE_STDCXX_11.  Yet, it still is
> there in the generated script, unexpanded.
OTOH, the "AX_" namespace is an arbitrary choice of the independently
maintained autoconf extension macro archive; autoconf neither explicitly
supports this, nor AFAIK reserves the namespace.  Thus, unless your
configure.ac, or some m4 file either explicitly, or implicitly included
by autoconf marks "AX_" as a reserved namespace, any macros within that
namespace which are undefined at autoconf run time will be silently
copied, unexpanded, in the generated configure script.

>> Did you regenerate the configure script _after_ you copied
>> the m4 macro definition to your aclocal directory?  The
>> diagnostic suggests that you didn't.
> 
> Now I did.
> 
>> I don't see any mention of an autoconf version constraint, in the
>> documentation, to which you refer, for AX_CXX_COMPILE_STDCXX_11;
>> what makes you think that there may be one?>
> I thought so because it didn't work after I "installed" this macro
> into /usr/share/aclocal/ .
It isn't sufficient to just dump a macro file in /usr/share/aclocal; you
need to ensure that configure.ac includes, either directly or
indirectly, an m4_include reference for that macro file, _and_ that
autoconf is told to search in /usr/local/aclocal -- IIRC, it may not
automatically search there, (but I may be wrong).

> Now that I have regenerated the configuration script, seen
> no warning about this macro, and it has remained unexpanded,
> I don't know what to suggest.  I have made sure my
> `autogen.sh' invokes `autoconf'.

But does it supply a "-I /usr/local/aclocal" argument, to set that
search path, and does configure.ac have an m4_include for the macro
file, (and ideally an m4_pattern_forbid notification for the "AX_"
namespace).

And BTW, if you are struggling with autotool issues, you may get more
focused advice from autoconf-mXXj517/[email protected] (for autoconf), or automake-mXXj517/[email protected]
(for automake).

-- 
Regards,
Keith.

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