Here's my latest revision of ntp_cacheversion.m4 with a bunch of shell
programming tweaks thanks to Eric, plus a change to not clear the
cache right after an empty cache file is created on the first run.
Thanks for the tips and comments.
Cheers,
Dave Hart
# NTP_CACHEVERSION(component, version)
# ------------------------------------
# compare this configure script's cache version stamp with the stamp
# saved by the prior run in config.cache. If they differ, clear all
# cache variables to avoid using results cached with a script that
# is known to differ in a cache-invalidating manner.
#
# Note: use immediately following AC_INIT in configure.ac, as clearing
# all _cv_ variables only makes sense immediately after loading, before
# use or modification.
#
# It is assumed that parent configure.ac files which use
# AC_CONFIG_SUBDIR to invoke child configure.ac files have used
# NTP_CACHEVERSION if any children do. The top-level configure script
# will clear a previous cache lacking any saved cache version number,
# while children do not. The reason is the children can rely on the
# parent having cleared any cache variables predating this mechanism.
# Therefore the child can rely on the config.cache generated by the
# parent on the first run despite not finding its version stamp
# previously saved.
AC_DEFUN_ONCE([NTP_CACHEVERSION], [
AC_BEFORE([$0], [AM_INIT_AUTOMAKE])dnl
AC_BEFORE([$0], [AM_CONFIG_HEADER])dnl
AC_BEFORE([$0], [AC_PROG_CC])dnl
ntp_cache_flush=1
case "$ntp_cv_[$1]_cache_version" in
[$2])
# same version, good
ntp_cache_flush=0
;;
'')
# No cache, predates ntp_cv_$1_cache_version, or is empty.
case "$cache_file" in
../*)
# Parent configure will have cleared cache once already.
# This will misfire if a top-level configure is invoked
# with --config-cache= value beginning with '../', is
# there a better way to detect this configure was
# invoked by a parent directory configure?
ntp_cache_flush=0
;;
/dev/null)
ntp_cache_flush=0
;;
*)
# This appears to be the top-level configure file.
# Do not clear the cache immediately after it is created
# empty as it is noisy. Differentiate a newly-created
# config.cache from one predating the cache version
# mechanism by looking for the first cached variable set
# by Autoconf
case "$ac_cv_path_install" in
'')
# presumably empty config.cache file
ntp_cache_flush=0
esac
esac
;;
*)
# configure cache version mismatches config.cache version
esac
case "$ntp_cache_flush" in
1)
# Clear all *_cv_* variables except our various components'
# ntp_cv_*_cache_version vars.
c_varname_list=`set |
sed -n -e 's/=.*$//' \
-e '/ntp_cv_.*_cache_version/d' \
-e '/_cv_/p'
`
for c_varname in $c_varname_list
do
dnl use AS_UNSET([$c_varname]) eventually
eval ${c_varname}=; $as_unset $c_varname
done
dnl use AS_UNSET([c_varname_list c_varname]) eventually
c_varname_list=; $as_unset c_varname_list c_varname
AC_MSG_NOTICE([$cache_file saved by another version, ignored.])
AC_MSG_NOTICE([configure script cache version: [$2]])
c_version="${ntp_cv_[$1]_cache_version:-(no version found)}"
AC_MSG_NOTICE([$cache_file version: $c_version])
$as_unset c_version
esac
# save configure version in config.cache for next time
ntp_cv_[$1]_cache_version="[$2]"
$as_unset ntp_cache_flush
])dnl
_______________________________________________
Autoconf mailing list
Autoconf@xxxxxxx
http://lists.gnu.org/mailman/listinfo/autoconf
