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Re: New substitution: top_build_prefix

From: Benoit Sigoure
Subject: Re: New substitution: top_build_prefix
Date: Sat, 10 Nov 2007 17:59:58 +0100

On Nov 10, 2007, at 12:00 PM, Ralf Wildenhues wrote:

* Ralf Wildenhues wrote on Thu, Nov 08, 2007 at 09:05:24PM CET:

  LIBLTDL = ${top_builddir}/ltdl/
    New config files output variable `top_build_prefix'.

Thanks to Paul and Benoit for reviewing my Autoconf patch.

Here's what I could think of for Libtool.  It's a bit ugly in that it
depends on the Autoconf version, and thus will fix the issue for AIX
make only once Autoconf 2.62 is used.

Hmm, do you think I could make the version comparison be against
`2.61a.265'? Do you see a more straightforward way to find out whether
Autoconf substitutes top_build_prefix, i.e., can I access `autom4te
--trace' results from within macro files? I could define a helper macro
in Autoconf, but that wouldn't feel much nicer either.

I'll wait for comments a couple of days before applying.

Hi Ralf,
thanks for addressing this. I must admit that I can't think of anything better than this (that is, doing the version comparison). I don't know whether you can access the trace result from within a macro, I don't think that's possible.

Your last solution has a very small advantage. Correct me if I'm wrong but basically the idea is to have some sort of witness macro in autoconf (_AC_HAVE_TOP_BUILD_PREFIX, or whatever) and libtool would try to expand it (if it expands => you can use ${top_build_prefix} / otherwise => fall back on ${top_builddir}) is that right? Well, this has the advantage that if this patch is backported by some distribution to an older version, libtool will correctly guess that $ {top_build_prefix} is usable even though you have an older autoconf. I think it might also help people that still deal with CVS autoconf (where the version number might be inaccurate or unreliable, as we have seen in Patrick's report yesterday).

All in all, either solution is sort of kludgy, but I have a slight preference for the helper macro in Autoconf.

2007-11-10  Ralf Wildenhues  <address@hidden>

        Use `${top_build_prefix}' for better compatibility with non-GNU make.
        * libltdl/m4/ltdl.m4 (_LT_BUILD_PREFIX): New macro.
        If the Autoconf version used is >= 2.62, then expand to
        `${top_build_prefix}', otherwise to `${top_builddir}/'.
        (LTDL_CONVENIENCE, LTDL_INSTALLABLE): Use it for defining
        LIBLTDL.  Fixes a build failure with AIX make in a package
        using convenience libltdl in nonrecursive mode.
        * doc/libtool.texi (Distributing libltdl): Document requirements
        to define `top_build_prefix' if Automake is not used.
        Report by Bob Friesenhahn.

Yeah, otherwise this also looks fine by me.

Benoit Sigoure aka Tsuna
EPITA Research and Development Laboratory

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