commit: write cache-tree data when writing index anyway

In prepare_index(), we refresh the index, and then write it to disk if
this changed the index data.  After running hooks we re-read the index
and compute the root tree sha1 with the cache-tree machinery.

This gives us a mostly free opportunity to write up-to-date cache-tree
data: we can compute it in prepare_index() immediately before writing
the index to disk.

If we do this, we were going to write the index anyway, and the later
cache-tree update has no further work to do.  If we don't do it, we
don't do any extra work, though we still don't have have cache-tree
data after the commit.

The only case that suffers badly is when the pre-commit hook changes
many trees in the index.  I'm writing this off as highly unusual.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/builtin/commit.c b/builtin/commit.c
index 4f782a3..5125841 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -394,6 +394,7 @@ static char *prepare_index(int argc, const char **argv, const char *prefix,
 		fd = hold_locked_index(&index_lock, 1);
 		add_files_to_cache(also ? prefix : NULL, pathspec, 0);
 		refresh_cache_or_die(refresh_flags);
+		update_main_cache_tree(1);
 		if (write_cache(fd, active_cache, active_nr) ||
 		    close_lock_file(&index_lock))
 			die(_("unable to write new_index file"));
@@ -414,6 +415,7 @@ static char *prepare_index(int argc, const char **argv, const char *prefix,
 		fd = hold_locked_index(&index_lock, 1);
 		refresh_cache_or_die(refresh_flags);
 		if (active_cache_changed) {
+			update_main_cache_tree(1);
 			if (write_cache(fd, active_cache, active_nr) ||
 			    commit_locked_index(&index_lock))
 				die(_("unable to write new_index file"));