git-version-gen: Honor GIT_DESCRIBE_FOR_BUILD environment variable

The GNOME-OSTree build system currently creates chroots and bind
mounts to the source tree outside the root; this means that we can't
necessarily run git inside the root, because in the case of git
submodules, the .git repository will point to outside root.

Also, error out fatally if we fail to determine the version; it
makes no sense to put UNKNOWN in e.g. the pkg-config files
since this will just cause errors later on.

configure.ac

@@ -28,6 +28,10 @@ AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_HEADERS([config.h])
 AM_INIT_AUTOMAKE([foreign 1.11 -Wall -Wno-portability silent-rules color-tests dist-xz tar-ustar])
 
+AS_IF([! test -n "$VERSION"], [
+   AC_MSG_ERROR([git-version-gen failed])
+])
+
 m4_define(pa_major, `echo $VERSION | cut -d. -f1 | cut -d- -f1`)
 m4_define(pa_minor, `echo $VERSION | cut -d. -f2 | cut -d- -f1`)
 

git-version-gen

@@ -1,6 +1,6 @@
 #!/bin/sh
 # Print a version string.
-scriptversion=2008-04-08.07.01
+scriptversion=2012-09-25.20
 
 # Copyright (C) 2007-2008 Free Software Foundation
 #
@@ -93,6 +93,15 @@ then
 	&& echo "$0: WARNING: $tarball_version_file seems to be damaged" 1>&2
 fi
 
+# This is presently used by the GNOME-OSTree build system; it
+# helps support the case where the meta-build system has already
+# determined the git revision, but we may not be able to run "git describe"
+# because we're inside a chroot.
+if test -n "$GIT_DESCRIBE_FOR_BUILD";
+then
+    v=$GIT_DESCRIBE_FOR_BUILD
+fi
+
 if test -n "$v"
 then
     : # use $v
@@ -133,7 +142,8 @@ then
 #    v=`echo "$v" | sed 's/-/./;s/\(.*\)-g/\1-/'`;
     :
 else
-    v=UNKNOWN
+    echo 1>&2 "$0: Failed to determine git revision"
+    exit 1
 fi
 
 v=`echo "$v" |sed 's/^v//'`