On 10 Aug 2010, at 15:19, Peter Rosin wrote:
> Hi!
Hi Peter,
> A macro by the name AM_PROG_AR might be on its way into Automake,
> and I would like to use it sooner rather than later. But I don't
> think it is prudent to require an Automake version which has the
> macro. Would something like this be a workable solution in
> libtool.m4 (untested, needs adjustments to _LT_CMD_OLD_ARCHIVE
> of course)?
>
> m4_ifndef([AM_PROG_AR],
>
> ############################################################
> # NOTE: A macro with the same interface as this has been #
> # submitted for inclusion into GNU Automake as #
> # AM_PROG_AR. When we require an Automake version which #
> # has this macro we should remove this macro from here #
> # and use the Automake macro unconditionally. #
> ############################################################
> [
> m4_defun([AM_PROG_AR],
> [AC_CHECK_TOOLS(AR, [ar], false)
> : ${AR=ar}
> AC_SUBST([AR])dnl
> ])# AM_PROG_AR
> ])
Just like that!
> Or how are situations like this generally handled?
Following, is a somewhat long-winded answer for the list archives
and the search engine indexing bots:
When I wanted to make use of modern (2.64 era) m4sugar facilities
in getopt.m4sh, but maintaining compatibility back to at least
Autoconf 2.62, I took this approach:
# m4go_expand(ARG)
# ----------------
# M4SH_GETOPTS wants to pass unbalanced parentheses to m4_expand to
# build the branches of a shell `case' statement. That is only
# supported by the implementation of m4_expand in Autoconf-2.64 and
# newer. Since we want to be compatible back to at least
# Autoconf-2.62, reimplement our own 2.64 based m4_expand in the
# m4go_ namespace so that we can be compatible with Autoconf versions
# supporting either semantic.
m4_define([m4go_expand],
[m4_chomp(_$0([$1
]))])
m4_define([_m4go_expand], [...])
However, I was worried about changing semantics between the various
releases, which is why I took a concrete implementation as a copy
of the simplest version, and renamed that into a known namespace.
By contrast, when we submitted AC_PROG_SED to Autoconf, we wrapped
the incumbent Libtool implementation in:
m4_ifndef([AC_PROG_SED], [
############################################################
# NOTE: This macro has been submitted for inclusion into #
# GNU Autoconf as AC_PROG_SED. When it is available in #
# a released version of Autoconf we should remove this #
# macro and use it instead. #
############################################################
m4_defun([AC_PROG_SED],
[...
])#AC_PROG_SED
])#m4_ifndef
The latter is closer to what you're aiming at, and thus I think your
proposal is perfectly fine :)
Cheers,
--
Gary V. Vaughan (g...@gnu.org)
