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|
# 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.
#
# The top-level configure.ac in a subtree using NTP_CACHEVERSION
# will clear a previous cache lacking any saved cache version number,
# while children do not. This comes into play only when introducing
# NTP_CACHEVERSION where it had not been previously used: Previous
# cached results are presumed incompatible and not used. The reason
# children do not flush the cached is it is shared with the parent and
# 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 the child version stamp in it.
#
# See html/copyright.html or COPYRIGHT in plain text.
AC_DEFUN_ONCE([NTP_CACHEVERSION], [
AC_BEFORE([$0], [AM_INIT_AUTOMAKE])dnl
AC_BEFORE([$0], [AC_CONFIG_HEADERS])dnl
AC_BEFORE([$0], [AC_PROG_CC])dnl
AC_BEFORE([$0], [AC_CONFIG_SUBDIRS])dnl
ntp_cache_flush=1
case "$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
/dev/null)
ntp_cache_flush=0
;;
*)
case "$NTP_CACHEVERSION_PARENT" in
'')
# Do not clear the cache immediately after it is created
# empty as it is noisy. Differentiate a newly-created
# config.cache from one predating the cache version
# mechanism by looking for the first cached variable set
# by Autoconf
case "$ac_cv_path_install" in
'')
# empty config.cache file
ntp_cache_flush=0
esac
;;
*)
# Parent configure just created cache from empty,
# flushing would be counterproductive.
ntp_cache_flush=0;
;;
esac
esac
;;
*)
# configure cache version mismatches config.cache version
;;
esac
case "$ntp_cache_flush" in
1)
c_version="${ntp_cv_[$1]_cache_version:-(no version found)}"
# Do we flush all variables or exclude others' version stamps?
case "$NTP_CACHEVERSION_PARENT" in
'')
# Clear all *_cv_* variables including our child subdirs'
# ntp_cv_*_cache_version variables. This prevents subdir
# configure scripts from noticing a version mismatch just
# after the top configure in the invocation cleared and
# recreated the cache.
c_varname_list=`set |
sed -n -e 's/=.*$//' \
-e '/_cv_/p'
`
;;
*)
# This is not the top configure this particular invocation.
# Clear all *_cv_* variables sparing the version stamps
# of other configure scripts, so we don't trigger
# useless repeated clearings.
c_varname_list=`set |
sed -n -e 's/=.*$//' \
-e '/ntp_cv_.*_cache_version/d' \
-e '/_cv_/p'
`
esac
for c_varname in $c_varname_list
do
dnl AS_UNSET([$c_varname])
dnl With Autoconf 2.61 and automake 1.10.3, using AS_UNSET
dnl here triggers generation of a syntax error in configure.
dnl Once we require a newer Autoconf we can revert to the
dnl AS_UNSET code.
{ eval $c_varname=; unset $c_varname; }
done
AC_MSG_NOTICE([[$cache_file saved by another version, ignored.]])
AC_MSG_NOTICE([[configure script cache version: ]][$2])
AC_MSG_NOTICE([[$cache_file version: $c_version]])
AS_UNSET([c_varname])
AS_UNSET([c_varname_list])
AS_UNSET([c_version])
esac
AS_UNSET([ntp_cache_flush])
# save configure version in config.cache for next time
ntp_cv_[$1]_cache_version="[$2]"
# let any subdir configure.ac NTP_CACHEVERSION invocations
# know they are not the top level.
NTP_CACHEVERSION_PARENT='[$1]' ; export NTP_CACHEVERSION_PARENT
])dnl
|
