object-name: make get_oid quietly return an error

A reasonable person looking at the signature and usage of get_oid and
friends might conclude that in the event of an error, it always returns
-1.  However, this is not the case.  Instead, get_oid_basic dies if we
go too far back into the history of a reflog (or, when quiet, simply
exits).

This is not especially useful, since in many cases, we might want to
handle this error differently.  Let's add a flag here to make it just
return -1 like elsewhere in these code paths.

Note that we cannot make this behavior the default, since we have many
other codepaths that rely on the existing behavior, including in tests.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

hash.h

@@ -216,6 +216,7 @@ struct object_id {
 #define GET_OID_REQUIRE_PATH         010000
 #define GET_OID_HASH_ANY             020000
 #define GET_OID_SKIP_AMBIGUITY_CHECK 040000
+#define GET_OID_GENTLY              0100000
 
 #define GET_OID_DISAMBIGUATORS \
 	(GET_OID_COMMIT | GET_OID_COMMITTISH | \

object-name.c

@@ -1081,13 +1081,17 @@ static int get_oid_basic(struct repository *r, const char *str, int len,
 				 * still fill in the oid with the "old" value,
 				 * which we can use.
 				 */
-			} else {
+			} else if (!(flags & GET_OID_GENTLY)) {
 				if (flags & GET_OID_QUIETLY) {
 					exit(128);
 				}
 				die(_("log for '%.*s' only has %d entries"),
 				    len, str, co_cnt);
 			}
+			if (flags & GET_OID_GENTLY) {
+				free(real_ref);
+				return -1;
+			}
 		}
 	}