diff: skip GITLINK when lazy fetching missing objs

In 7fbbcb21b1 ("diff: batch fetching of missing blobs", 2019-04-08),
diff was taught to batch the fetching of missing objects when operating
on a partial clone, but was not taught to refrain from fetching
GITLINKs. Teach diff to check if an object is a GITLINK before including
it in the set to be fetched.

(As stated in the commit message of that commit, unpack-trees was also
taught a similar thing prior, but unpack-trees correctly checks for
GITLINK before including objects in the set to be fetched.)

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

1 files changed, 1 insertions, 0 deletions

diff --git a/diff.c b/diff.c
index 1ccd96bbfd..9a2aa07a0e 100644
--- a/diff.c
+++ b/diff.c
@@ -6487,6 +6487,7 @@ static void add_if_missing(struct repository *r,
 			   const struct diff_filespec *filespec)
 {
 	if (filespec && filespec->oid_valid &&
+	    !S_ISGITLINK(filespec->mode) &&
 	    oid_object_info_extended(r, &filespec->oid, NULL,
 				     OBJECT_INFO_FOR_PREFETCH))
 		oid_array_append(to_fetch, &filespec->oid);