build: Use Gnulib's 'git-version-gen'.

* Makefile.am (EXTRA_DIST, BUILT_SOURCES): Add $(top_srcdir)/.version.
($(top_srcdir)/.version, gen-tarball-version): New targets.
(dist-hook): Depend on 'gen-tarball-version'.
(.PHONY): Add 'gen-tarball-version'.
* build-aux/git-version-gen: New file, from Gnulib v0.1-1312-ga87d5e5c6.
* configure.ac: Use it in 'AC_INIT'.  Use 'https' for the URL.

4 files changed, 242 insertions, 4 deletions

diff --git a/.gitignore b/.gitignore
index 1fc22d7e93..cff056a9d7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -125,3 +125,4 @@ tmp
 /doc/os-config-lightweight-desktop.texi
 /nix/scripts/download
 /etc/indent-code.el
+/.version
diff --git a/Makefile.am b/Makefile.am
index 64d8d31cfe..8fe9e350cc 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -510,11 +510,19 @@ guix-binary.%.tar.xz:
 	cp "$$tarball" "$@.tmp" ; mv "$@.tmp" "$@"
 
 
-dist-hook: gen-ChangeLog gen-AUTHORS
+dist-hook: gen-ChangeLog gen-AUTHORS gen-tarball-version
 dist-hook: assert-no-store-file-names
 
 distcheck-hook: assert-binaries-available assert-final-inputs-self-contained
 
+EXTRA_DIST += $(top_srcdir)/.version
+BUILT_SOURCES += $(top_srcdir)/.version
+$(top_srcdir)/.version:
+	echo $(VERSION) > "$@-t" && mv "$@-t" "$@"
+
+gen-tarball-version:
+	echo $(VERSION) > "$(distdir)/.tarball-version"
+
 gen-ChangeLog:
 	$(AM_V_GEN)if test -d .git; then		\
 	  $(top_srcdir)/build-aux/gitlog-to-changelog	\
@@ -562,9 +570,10 @@ hydra-jobs.scm: $(GOBJECTS)
 	  "$(top_srcdir)/build-aux/hydra/gnu-system.scm" > "$@.tmp"
 	$(AM_V_at)mv "$@.tmp" "$@"
 
-.PHONY: gen-ChangeLog gen-AUTHORS clean-go make-go
+.PHONY: gen-ChangeLog gen-AUTHORS gen-tarball-version
 .PHONY: assert-no-store-file-names assert-binaries-available
 .PHONY: assert-final-inputs-self-contained
+.PHONY: clean-go make-go
 
 ## -------------- ##
 ## Silent rules.  ##
diff --git a/build-aux/git-version-gen b/build-aux/git-version-gen
new file mode 100755
index 0000000000..079849d5e5
--- /dev/null
+++ b/build-aux/git-version-gen
@@ -0,0 +1,226 @@
+#!/bin/sh
+# Print a version string.
+scriptversion=2017-01-09.19; # UTC
+
+# Copyright (C) 2007-2017 Free Software Foundation, Inc.
+#
+# 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 <http://www.gnu.org/licenses/>.
+
+# This script is derived from GIT-VERSION-GEN from GIT: http://git.or.cz/.
+# It may be run two ways:
+# - from a git repository in which the "git describe" command below
+#   produces useful output (thus requiring at least one signed tag)
+# - from a non-git-repo directory containing a .tarball-version file, which
+#   presumes this script is invoked like "./git-version-gen .tarball-version".
+
+# In order to use intra-version strings in your project, you will need two
+# separate generated version string files:
+#
+# .tarball-version - present only in a distribution tarball, and not in
+#   a checked-out repository.  Created with contents that were learned at
+#   the last time autoconf was run, and used by git-version-gen.  Must not
+#   be present in either $(srcdir) or $(builddir) for git-version-gen to
+#   give accurate answers during normal development with a checked out tree,
+#   but must be present in a tarball when there is no version control system.
+#   Therefore, it cannot be used in any dependencies.  GNUmakefile has
+#   hooks to force a reconfigure at distribution time to get the value
+#   correct, without penalizing normal development with extra reconfigures.
+#
+# .version - present in a checked-out repository and in a distribution
+#   tarball.  Usable in dependencies, particularly for files that don't
+#   want to depend on config.h but do want to track version changes.
+#   Delete this file prior to any autoconf run where you want to rebuild
+#   files to pick up a version string change; and leave it stale to
+#   minimize rebuild time after unrelated changes to configure sources.
+#
+# As with any generated file in a VC'd directory, you should add
+# /.version to .gitignore, so that you don't accidentally commit it.
+# .tarball-version is never generated in a VC'd directory, so needn't
+# be listed there.
+#
+# Use the following line in your configure.ac, so that $(VERSION) will
+# automatically be up-to-date each time configure is run (and note that
+# since configure.ac no longer includes a version string, Makefile rules
+# should not depend on configure.ac for version updates).
+#
+# AC_INIT([GNU project],
+#         m4_esyscmd([build-aux/git-version-gen .tarball-version]),
+#         [bug-project@example])
+#
+# Then use the following lines in your Makefile.am, so that .version
+# will be present for dependencies, and so that .version and
+# .tarball-version will exist in distribution tarballs.
+#
+# EXTRA_DIST = $(top_srcdir)/.version
+# BUILT_SOURCES = $(top_srcdir)/.version
+# $(top_srcdir)/.version:
+#	echo $(VERSION) > $@-t && mv $@-t $@
+# dist-hook:
+#	echo $(VERSION) > $(distdir)/.tarball-version
+
+
+me=$0
+
+version="git-version-gen $scriptversion
+
+Copyright 2011 Free Software Foundation, Inc.
+There is NO warranty.  You may redistribute this software
+under the terms of the GNU General Public License.
+For more information about these matters, see the files named COPYING."
+
+usage="\
+Usage: $me [OPTION]... \$srcdir/.tarball-version [TAG-NORMALIZATION-SED-SCRIPT]
+Print a version string.
+
+Options:
+
+   --prefix PREFIX    prefix of git tags (default 'v')
+   --fallback VERSION
+                      fallback version to use if \"git --version\" fails
+
+   --help             display this help and exit
+   --version          output version information and exit
+
+Running without arguments will suffice in most cases."
+
+prefix=v
+fallback=
+
+while test $# -gt 0; do
+  case $1 in
+    --help) echo "$usage"; exit 0;;
+    --version) echo "$version"; exit 0;;
+    --prefix) shift; prefix=${1?};;
+    --fallback) shift; fallback=${1?};;
+    -*)
+      echo "$0: Unknown option '$1'." >&2
+      echo "$0: Try '--help' for more information." >&2
+      exit 1;;
+    *)
+      if test "x$tarball_version_file" = x; then
+        tarball_version_file="$1"
+      elif test "x$tag_sed_script" = x; then
+        tag_sed_script="$1"
+      else
+        echo "$0: extra non-option argument '$1'." >&2
+        exit 1
+      fi;;
+  esac
+  shift
+done
+
+if test "x$tarball_version_file" = x; then
+    echo "$usage"
+    exit 1
+fi
+
+tag_sed_script="${tag_sed_script:-s/x/x/}"
+
+nl='
+'
+
+# Avoid meddling by environment variable of the same name.
+v=
+v_from_git=
+
+# First see if there is a tarball-only version file.
+# then try "git describe", then default.
+if test -f $tarball_version_file
+then
+    v=`cat $tarball_version_file` || v=
+    case $v in
+        *$nl*) v= ;; # reject multi-line output
+        [0-9]*) ;;
+        *) v= ;;
+    esac
+    test "x$v" = x \
+        && echo "$0: WARNING: $tarball_version_file is missing or damaged" 1>&2
+fi
+
+if test "x$v" != x
+then
+    : # use $v
+# Otherwise, if there is at least one git commit involving the working
+# directory, and "git describe" output looks sensible, use that to
+# derive a version string.
+elif test "`git log -1 --pretty=format:x . 2>&1`" = x \
+    && v=`git describe --abbrev=4 --match="$prefix*" HEAD 2>/dev/null \
+          || git describe --abbrev=4 HEAD 2>/dev/null` \
+    && v=`printf '%s\n' "$v" | sed "$tag_sed_script"` \
+    && case $v in
+         $prefix[0-9]*) ;;
+         *) (exit 1) ;;
+       esac
+then
+    # Is this a new git that lists number of commits since the last
+    # tag or the previous older version that did not?
+    #   Newer: v6.10-77-g0f8faeb
+    #   Older: v6.10-g0f8faeb
+    case $v in
+        *-*-*) : git describe is okay three part flavor ;;
+        *-*)
+            : git describe is older two part flavor
+            # Recreate the number of commits and rewrite such that the
+            # result is the same as if we were using the newer version
+            # of git describe.
+            vtag=`echo "$v" | sed 's/-.*//'`
+            commit_list=`git rev-list "$vtag"..HEAD 2>/dev/null` \
+                || { commit_list=failed;
+                     echo "$0: WARNING: git rev-list failed" 1>&2; }
+            numcommits=`echo "$commit_list" | wc -l`
+            v=`echo "$v" | sed "s/\(.*\)-\(.*\)/\1-$numcommits-\2/"`;
+            test "$commit_list" = failed && v=UNKNOWN
+            ;;
+    esac
+
+    # Change the first '-' to a '.', so version-comparing tools work properly.
+    # Remove the "g" in git describe's output string, to save a byte.
+    v=`echo "$v" | sed 's/-/./;s/\(.*\)-g/\1-/'`;
+    v_from_git=1
+elif test "x$fallback" = x || git --version >/dev/null 2>&1; then
+    v=UNKNOWN
+else
+    v=$fallback
+fi
+
+v=`echo "$v" |sed "s/^$prefix//"`
+
+# Test whether to append the "-dirty" suffix only if the version
+# string we're using came from git.  I.e., skip the test if it's "UNKNOWN"
+# or if it came from .tarball-version.
+if test "x$v_from_git" != x; then
+  # Don't declare a version "dirty" merely because a timestamp has changed.
+  git update-index --refresh > /dev/null 2>&1
+
+  dirty=`exec 2>/dev/null;git diff-index --name-only HEAD` || dirty=
+  case "$dirty" in
+      '') ;;
+      *) # Append the suffix only if there isn't one already.
+          case $v in
+            *-dirty) ;;
+            *) v="$v-dirty" ;;
+          esac ;;
+  esac
+fi
+
+# Omit the trailing newline, so that m4_esyscmd can use the result directly.
+printf %s "$v"
+
+# Local variables:
+# eval: (add-hook 'write-file-hooks 'time-stamp)
+# time-stamp-start: "scriptversion="
+# time-stamp-format: "%:y-%02m-%02d.%02H"
+# time-stamp-time-zone: "UTC0"
+# time-stamp-end: "; # UTC"
+# End:
diff --git a/configure.ac b/configure.ac
index 2b4620c44b..dc3d8f377f 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2,8 +2,10 @@
 # Process this file with autoconf to produce a configure script.
 
 AC_PREREQ(2.68)
-AC_INIT([GNU Guix], [0.12.0], [bug-guix@gnu.org], [guix],
-  [http://www.gnu.org/software/guix/])
+AC_INIT([GNU Guix],
+  [m4_esyscmd([build-aux/git-version-gen .tarball-version])],
+  [bug-guix@gnu.org], [guix],
+  [https://www.gnu.org/software/guix/])
 AC_CONFIG_AUX_DIR([build-aux])
 
 AM_INIT_AUTOMAKE([1.12 gnu silent-rules subdir-objects \