diff options
Diffstat (limited to 'm4/ntp_cacheversion.m4')
| -rw-r--r-- | m4/ntp_cacheversion.m4 | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/m4/ntp_cacheversion.m4 b/m4/ntp_cacheversion.m4 new file mode 100644 index 0000000000000..bf27b89130d17 --- /dev/null +++ b/m4/ntp_cacheversion.m4 @@ -0,0 +1,120 @@ +# 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. In this case top-level means a configure script +# not invoked by another configure script in its parent directory. + +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 + 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 $c_varname_list + do + AS_UNSET([$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 |