Store build time

configure.ac

@@ -11,7 +11,6 @@ AM_INIT_AUTOMAKE([foreign -Wall subdir-objects])
 AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_HEADERS([config.h])
 AM_SILENT_RULES([yes])
-
 # ABI version
 #
 # Set the libtool library version, see LIBRARY_INTERFACE
@@ -36,6 +35,8 @@ AC_DEFINE([$1], [$2], [$3])
 AC_SUBST([$1], ['$2'])
 ])
 
+AX_BUILD_DATE_EPOCH(ELPA_BUILDTIME)
+
 # API Version
 AC_DEFINE([EARLIEST_API_VERSION], [20170403], [Earliest supported ELPA API version])
 
@@ -44,6 +45,8 @@ AC_DEFINE_SUBST(CURRENT_API_VERSION, 20200417, "Current ELPA API version")
 AC_DEFINE([EARLIEST_AUTOTUNE_VERSION], [20171201], [Earliest ELPA API version, which supports autotuning])
 AC_DEFINE([CURRENT_AUTOTUNE_VERSION], [20200417], [Current ELPA autotune version])
 AC_DEFINE_SUBST(CURRENT_AUTOTUNE_VERSION, 20200417, "Current ELPA autotune version")
+AC_DEFINE_UNQUOTED([ELPA_BUILDTIME], [$ELPA_BUILDTIME], ["Time of build"])
+
 
 AX_CHECK_GNU_MAKE()
 if test x$_cv_gnu_make_command = x ; then
@@ -51,7 +54,6 @@ if test x$_cv_gnu_make_command = x ; then
 fi
 
 enable_legacy=no
-
 AC_MSG_CHECKING(whether in C interface the error argument should be optional)
 AC_ARG_ENABLE([optional-argument-in-C-API],
               AS_HELP_STRING([--enable-optional-argument-in-C-API],

m4/ax_build_date_epoch.m4

+#
+# DESCRIPTION
+#
+#   Sets VARIABLE to a string representing the current time.  It is
+#   formatted according to FORMAT if specified, otherwise it is formatted as
+#   the number of seconds (excluding leap seconds) since the UNIX epoch (01
+#   Jan 1970 00:00:00 UTC).
+#
+#   If the SOURCE_DATE_EPOCH environment variable is set, it uses the value
+#   of that variable instead of the current time.  See
+#   https://reproducible-builds.org/specs/source-date-epoch).  If
+#   SOURCE_DATE_EPOCH is set but cannot be properly interpreted as a UNIX
+#   timestamp, then execute ACTION-IF-FAIL if specified, otherwise error.
+#
+#   VARIABLE is AC_SUBST-ed.
+#
+# LICENSE
+#
+#   Copyright (c) 2016 Eric Bavier <bavier@member.fsf.org>
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 2
+
+AC_DEFUN([AX_BUILD_DATE_EPOCH],
+[dnl
+AC_MSG_CHECKING([for build time])
+ax_date_fmt="m4_default($2,%s)"
+AS_IF([test x"$SOURCE_DATE_EPOCH" = x],
+ [$1=`date "+$ax_date_fmt"`],
+ [ax_build_date=`date -u -d "@$SOURCE_DATE_EPOCH" "+$ax_date_fmt" 2>/dev/null \
+                 || date -u -r "$SOURCE_DATE_EPOCH" "+$ax_date_fmt" 2>/dev/null`
+  AS_IF([test x"$ax_build_date" = x],
+   [m4_ifval([$3],
+      [$3],
+      [AC_MSG_ERROR([malformed SOURCE_DATE_EPOCH])])],
+   [$1=$ax_build_date])])
+AC_MSG_RESULT([$$1])
+])dnl AX_BUILD_DATE_EPOCH
+