object API users + docs: check <0, not !0 with check_object_signature()

Change those users of the object API that misused
check_object_signature() by assuming it returned any non-zero when the
OID didn't match the expected value to check <0 instead. In practice
all of this code worked before, but it wasn't consistent with rest of
the users of the API.

Let's also clarify what the <0 return value means in API docs.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/cache.h b/cache.h
index 98d1ef0857..5d08195212 100644
--- a/cache.h
+++ b/cache.h
@@ -1324,6 +1324,9 @@ int parse_loose_header(const char *hdr, struct object_info *oi);
  * object name actually matches "oid" to detect object corruption.
  * With "buf" == NULL, try reading the object named with "oid" using
  * the streaming interface and rehash it to do the same.
+ *
+ * A negative value indicates an error, usually that the OID is not
+ * what we expected, but it might also indicate another error.
  */
 int check_object_signature(struct repository *r, const struct object_id *oid,
 			   void *buf, unsigned long size, const char *type,