Re: "git commit --amend --only --" nevertheless commits staged changes

Marc Strapetz [off-list ref] writes:

When using "git commit --amend --only --message <message> --", I'd
expect to have just the commit message of my last commit changed,
according to the man page:

"--only Make a commit only from the paths specified on the command line,
disregarding any contents that have been staged so far. [...] If this
option is specified together with --amend, then no paths need to be
specified, which can be used to amend the last commit without committing
changes that have already been staged."

However, all staged changes are committed as well. So looks like either
the man page or Git is wrong here!?

I do not think the combination with --amend, --only and no paths
ever worked.  We rejected such a combination before 6a74642c5, which
merely made us to accept the combination but I do not think the
commit did anything to re-read the tree from the HEAD being amended
to the index.

Something like this, but I haven't thought about what other things
it may break.

 builtin/commit.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index f43eaaf..59ef5e1 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c

@@ -184,6 +184,9 @@ static int list_paths(struct string_list *list, const char *with_tree,
 	int i;
 	char *m;
 
+	if (!pattern)
+		return 0;
+
 	for (i = 0; pattern[i]; i++)
 		;
 	m = xcalloc(1, i);

@@ -345,7 +348,7 @@ static char *prepare_index(int argc, const char **argv, const char *prefix,
 	 * and create commit from the_index.
 	 * We still need to refresh the index here.
 	 */
-	if (!pathspec || !*pathspec) {
+	if (!(only && amend) && (!pathspec || !*pathspec)) {
 		fd = hold_locked_index(&index_lock, 1);
 		refresh_cache_or_die(refresh_flags);
 		if (active_cache_changed) {