[PATCH] Do not generate full commit log message if it not going to be used

[Alex Riesen <raa.lkml@gmail.com>]

Like when it is already specified through -C, -F or -m to git-commit.

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
---

Alex Riesen, Tue, Nov 27, 2007 19:18:56 +0100:
> On 27/11/2007, Junio C Hamano <gitster@pobox.com> wrote:
> > ... When no_edit is in effect, I think these two places can
> > be replaced with an equivalent of "diff-index --cached HEAD --" (which
> > should not hit the work tree at all) to see if there is anything to be
> > committed.  For initial commit the check would obviously be "is the
> > index empty?" instead.
> 
> This is of course very useful optimization, and will speed up things
> everywhere (and especially here).

Could not stop myself. Hopefully didn't beat anyone to it :)
Almost all code shamelessly stolen from builtin-diff-index.c.
Builds, runs, passes all the tests. That !active_nr is
micro-optimization, but a nice one: clearly don't reread.

Preprocessor trickery in DIFF_OPT_* macros is disgusting, it breaks
Vim word completion and trying to use many flags in one expression
looks just ugly. What was wrong is inline functions?

 builtin-commit.c |   24 ++++++++++++++++++++++++
 1 files changed, 24 insertions(+), 0 deletions(-)

diff --git a/builtin-commit.c b/builtin-commit.c
index a35881e..8167ce4 100644
--- a/builtin-commit.c
+++ b/builtin-commit.c
@@ -367,6 +367,30 @@ static int prepare_log_message(const char *index_file, const char *prefix)
 
 	strbuf_release(&sb);
 
+	if (no_edit) {
+		static const char *argv[] = { NULL, "HEAD", NULL };
+		struct rev_info rev;
+		unsigned char sha1[40];
+		int is_initial;
+
+		fclose(fp);
+
+		if (!active_nr && read_cache() < 0)
+			die("Cannot read index");
+
+		if (get_sha1("HEAD", sha1) != 0)
+			return !!active_nr;
+
+		init_revisions(&rev, "");
+		rev.abbrev = 0;
+		(void)setup_revisions(2, argv, &rev, NULL);
+		DIFF_OPT_SET(&rev.diffopt, QUIET);
+		DIFF_OPT_SET(&rev.diffopt, EXIT_WITH_STATUS);
+		(void)run_diff_index(&rev, 1 /* cached */);
+
+		return !!DIFF_OPT_TST(&rev.diffopt, HAS_CHANGES);
+	}
+
 	if (in_merge && !no_edit)
 		fprintf(fp,
 			"#\n"
-- 
1.5.3.6.1006.g08f2