Re: Addressing sources dynamically generated by autoconf

[Thomas Jahns]

On Nov 21, 2022, at 18:37 , Russ Allbery <eagle@eyrie.org> wrote:
> Thomas Jahns <jahns@dkrz.de> writes:
> 
>> I know I can write a Makefile.in myself, but given the number of
>> additional targets users expect, I'd really prefer sticking to build
>> instructions as much as possible and delegate dist, check and other
>> targets to automake. I also know about AC_LIBOBJS, but this facility
>> only seems to address a list of sources I can provide in a verbatim way
>> and not necessarily via some macro or shell variable even, but I'd like
>> to be wrong about that.
> 
> AC_LIBOBJ feels like the right mechanism to me, but perhaps I don't
> understand what you're trying to do.  It does seem to do exactly what you
> are talking about, though: substitute in additional sources based on
> Autoconf results without having to list them explicitly in Makefile.am.
> 
> I think the problem you may be running into is that AC_LIBOBJ requires
> that the file name you give it as an argument be a source file that is
> included in the distribution tarball, whereas you want to generate that
> source file on the fly.  But you can work around that with a bit of
> trickery.  Suppose that you have some probe that conditionally calls
> AC_LIBOBJ([mpich-fix]) based on whether you detect that there's a problem.
> You can then include mpich-fix.c in your distribution tarball as a
> one-line file that contains only:
> 
> #include "mpich-fix-real.c"
> 
> mpich-fix-real.c is *not* included in your distribution tarball.  If the
> configure check succeeds, this file is never added to the sources and thus
> is never compiled and the fact the file doesn't exist doesn't matter.  If
> the configure check fails and you need to fix something, then configure
> generates the file mpich-fix-real.c on the fly, Automake adds mpich-real.o
> to LIBOBJS/LTLIBOBJS, and the compiler follows the #include and builds
> your generated code.
> 
> Does that get at the problem that you're having?


Thanks, I hadn't thought of doing that redirection via #include, it might just 
work. I will need to add some boilerplate files, so I'm open to further 
suggestions if that can be made unnecessary. But otherwise, going for #include 
instead of copying appears workable.

Regards, Thomas

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