[PATCH] commit: write out cache-tree information

[<trast@student.ethz.ch>]

From: Thomas Rast <trast@student.ethz.ch>

While write-tree has code to write out the cache-tree information
(since we have to compute it anyway if the cache is stale), commit
lost this capability when it became a builtin and moved away from
using write-tree.

Add the necessary code to write out the cache.  This is extremely
similar to what write_cache_as_tree() does.

Reported-by: Carlos Martín Nieto <cmn@elego.de>
Signed-off-by: Thomas Rast <trast@student.ethz.ch>
---

Reported on IRC.

There's a similar disparity between read-tree and checkout, but I
first have to understand the exact conditions in or around
unpack_trees() [checkout.c:417] where the read-tree reasoning applies.

 builtin/commit.c |    9 +++++++++
 1 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index e1af9b1..47b0eea 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -637,6 +637,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	const char *hook_arg2 = NULL;
 	int ident_shown = 0;
 	int clean_message_contents = (cleanup_mode != CLEANUP_NONE);
+	int fd;
+	struct lock_file *lock_file;
 
 	if (!no_verify && run_hook(index_file, "pre-commit", NULL))
 		return 0;
@@ -861,6 +863,8 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 	 * the editor and after we invoke run_status above.
 	 */
 	discard_cache();
+	lock_file = xcalloc(1, sizeof(struct lock_file));
+	fd = hold_lock_file_for_update(lock_file, index_file, LOCK_DIE_ON_ERROR);
 	read_cache_from(index_file);
 	if (!active_cache_tree)
 		active_cache_tree = cache_tree();
@@ -869,6 +873,11 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		error(_("Error building trees"));
 		return 0;
 	}
+	if (0 <= fd) {
+		if (write_cache(fd, active_cache, active_nr) ||
+		    commit_lock_file(lock_file))
+			rollback_lock_file(lock_file);
+	}
 
 	if (run_hook(index_file, "prepare-commit-msg",
 		     git_path(commit_editmsg), hook_arg1, hook_arg2, NULL))
-- 
1.7.6.668.g17b0a