Allow GIT version to be used in pacman builds

Add a new configure flag, --enable-git-version, that allows the output of
'git describe' to be used in the version string associated with this
package. This could aid in debugging for users that are using a development
version of pacman and we should be able to figure out which cut of code they
are using.

Sample output:
$ pacman --version
Pacman v3.1.4-190-g4cfa-dirty - libalpm v2.3.1

$ makepkg --version
makepkg (pacman) 3.1.4-190-g5861-dirty

Signed-off-by: Dan McGee <dan@archlinux.org>

2 files changed, 11 insertions, 0 deletions

diff --git a/src/pacman/Makefile.am b/src/pacman/Makefile.am
index 5d6fef3c..e5f8cb36 100644
--- a/src/pacman/Makefile.am
+++ b/src/pacman/Makefile.am
@@ -21,6 +21,11 @@ INCLUDES = -I$(top_srcdir)/lib/libalpm
 
 AM_CFLAGS = -pedantic -D_GNU_SOURCE
 
+if USE_GIT_VERSION
+GIT_VERSION := $(shell sh -c 'git describe --abbrev=4 | sed s/^v//')-dirty
+DEFS += -DGIT_VERSION=\"$(GIT_VERSION)\"
+endif
+
 pacman_SOURCES = \
 	conf.h conf.c \
 	deptest.c \
diff --git a/src/pacman/pacman.c b/src/pacman/pacman.c
index 66fafa10..0ce9c1e8 100644
--- a/src/pacman/pacman.c
+++ b/src/pacman/pacman.c
@@ -19,6 +19,12 @@
 
 #include "config.h"
 
+/* special handling of package version for GIT */
+#if defined(GIT_VERSION)
+#undef PACKAGE_VERSION
+#define PACKAGE_VERSION GIT_VERSION
+#endif
+
 #include <stdlib.h> /* atoi */
 #include <stdio.h>
 #include <limits.h>