diff: make sure work tree side is shown as 0{40} when different

Ping Yin noticed that "git diff-index --raw" shows 0{40} when work tree
has submodule difference, but "git diff --raw" didn't correctly do so.

There was a mistake in the diffcore_skip_stat_unmatch() that was meant to
clean up the stat-only difference for running diff between the index and
work tree and diff between the tree and the work tree, to cause it re-read
from the submodule repository HEAD.  When ce_stat_match() says work tree
is different, we should always say 0{40} on the work tree side.

This patch fixes the issue, and adds tests.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 5 deletions

diff --git a/diff.c b/diff.c
index b80f656..00e1590 100644
--- a/diff.c
+++ b/diff.c
@@ -3187,11 +3187,8 @@ static void diffcore_apply_filter(const char *filter)
 static int diff_filespec_is_identical(struct diff_filespec *one,
 				      struct diff_filespec *two)
 {
-	if (S_ISGITLINK(one->mode)) {
-		diff_fill_sha1_info(one);
-		diff_fill_sha1_info(two);
-		return !hashcmp(one->sha1, two->sha1);
-	}
+	if (S_ISGITLINK(one->mode))
+		return 0;
 	if (diff_populate_filespec(one, 0))
 		return 0;
 	if (diff_populate_filespec(two, 0))