Re: New substitution: top_build_prefix

[Ralf Wildenhues]

* Eric Blake wrote on Sat, Nov 10, 2007 at 08:20:27PM CET:
> According to Ralf Wildenhues on 11/10/2007 4:00 AM:
> 
> > Hmm, do you think I could make the version comparison be against
> > `2.61a.265'?
> 
> Yes, that will work, thanks to my recent fix to m4_version_unletter...
> 
> >  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.
> 
> although I kind of like Benoit's suggestion of also providing a witness
> macro in autoconf, so that the test can be made independent of whether the
> patch is backported to earlier autoconf versions.

OK.  Thanks for the reviews, Benoit and Eric.  This is what I've added
to Autoconf.

Another nitty gritty detail: should I leave in the version check >= 2.62
in Libtool so that future Autoconf versions will not need to carry
around the witness macro baggage?

Cheers,
Ralf

    Add witness macro for @top_build_prefix@ substitution.
    
    * lib/autoconf/status.m4 (_AC_HAVE_TOP_BUILD_PREFIX): New macro.
    (_AC_OUTPUT_FILE): Mention it here.

diff --git a/lib/autoconf/status.m4 b/lib/autoconf/status.m4
index 487cc01..0d1d93e 100644
--- a/lib/autoconf/status.m4
+++ b/lib/autoconf/status.m4
@@ -136,6 +136,11 @@ ac_abs_srcdir=$ac_abs_top_srcdir$ac_dir_suffix
 ])# _AC_SRCDIRS
 
 
+# _AC_HAVE_TOP_BUILD_PREFIX
+# -------------------------
+# Announce to the world (to Libtool) that we substitute @address@hidden
+AC_DEFUN([_AC_HAVE_TOP_BUILD_PREFIX])
+
 
 ## ---------------------- ##
 ## Registering the tags.  ##
@@ -622,6 +627,7 @@ dnl configure_input is a somewhat special, so we don't call 
AC_SUBST_TRACE.
 s&@configure_input@&$configure_input&;t t
 dnl During the transition period, this is a special case:
 s&@top_builddir@&$ac_top_builddir_sub&;t t[]AC_SUBST_TRACE([top_builddir])
+dnl For this substitution see the witness macro _AC_HAVE_TOP_BUILD_PREFIX 
above.
 s&@top_build_prefix@&$ac_top_build_prefix&;t 
t[]AC_SUBST_TRACE([top_build_prefix])
 m4_foreach([_AC_Var], [srcdir, abs_srcdir, top_srcdir, abs_top_srcdir,
                        builddir, abs_builddir,