Re: 'git commit --short' without touching index?

Jeff King [off-list ref] writes:

On Mon, Jul 05, 2010 at 01:10:43PM -0700, Junio C Hamano wrote:

quoted

Jeff King [off-list ref] writes:

quoted

It would be nice if the index-refreshing code only wrote to the index if
there was something worth writing. I'm not sure how hard that would be
to implement, though.

Hmm, don't we already do that with "istate->cache_changed"?

Apparently not:

  $ stat .git/index | grep -i modify
  Modify: 2010-07-05 16:52:11.000000000 -0400
  $ git status
  # On branch master
  nothing to commit
  $ stat .git/index | grep -i modify
  Modify: 2010-07-05 16:53:09.000000000 -0400

and it is not just updating some stat-dirtiness. Doing it over and over
will keep updating the index. It looks like we unconditionally do the
lock and write in cmd_status, but I haven't looked further.

Something like this, plus possibly a similar fix to "git commit $path"
codepath, perhaps?

We may want to audit all uses of write_cache() and write_index() that are
not protected with active_cache_changed (or istate->cache_changed); I am
reluctant to suggest placing that logic into write_index() at this point,
though, as we may be updating the index in bulk, without marking
active_cache_changed bit, exactly because we know we will unconditionally
write the result out.

 builtin/commit.c |   10 +++++++---
 1 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index c101f00..86d3926 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c

@@ -343,9 +343,13 @@ static char *prepare_index(int argc, const char **argv, const char *prefix, int
 	if (!pathspec || !*pathspec) {
 		fd = hold_locked_index(&index_lock, 1);
 		refresh_cache_or_die(refresh_flags);
-		if (write_cache(fd, active_cache, active_nr) ||
-		    commit_locked_index(&index_lock))
-			die("unable to write new_index file");
+		if (active_cache_changed) {
+			if (write_cache(fd, active_cache, active_nr) ||
+			    commit_locked_index(&index_lock))
+				die("unable to write new_index file");
+		} else {
+			rollback_lock_file(&index_lock);
+		}
 		commit_style = COMMIT_AS_IS;
 		return get_index_file();
 	}