fsck: report errors if reflog entries point at invalid objects

Previously, if a reflog entry's old or new SHA-1 was not resolvable to
an object, that SHA-1 was silently ignored. Instead, report such cases
as errors.

Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fsck.c

@@ -451,7 +451,7 @@ static void fsck_dir(int i, char *path)
 
 static int default_refs;
 
-static void fsck_handle_reflog_sha1(unsigned char *sha1)
+static void fsck_handle_reflog_sha1(const char *refname, unsigned char *sha1)
 {
 	struct object *obj;
 
@@ -460,6 +460,9 @@ static void fsck_handle_reflog_sha1(unsigned char *sha1)
 		if (obj) {
 			obj->used = 1;
 			mark_object_reachable(obj);
+		} else {
+			error("%s: invalid reflog entry %s", refname, sha1_to_hex(sha1));
+			errors_found |= ERROR_REACHABLE;
 		}
 	}
 }
@@ -468,18 +471,20 @@ static int fsck_handle_reflog_ent(unsigned char *osha1, unsigned char *nsha1,
 		const char *email, unsigned long timestamp, int tz,
 		const char *message, void *cb_data)
 {
+	const char *refname = cb_data;
+
 	if (verbose)
 		fprintf(stderr, "Checking reflog %s->%s\n",
 			sha1_to_hex(osha1), sha1_to_hex(nsha1));
 
-	fsck_handle_reflog_sha1(osha1);
-	fsck_handle_reflog_sha1(nsha1);
+	fsck_handle_reflog_sha1(refname, osha1);
+	fsck_handle_reflog_sha1(refname, nsha1);
 	return 0;
 }
 
 static int fsck_handle_reflog(const char *logname, const unsigned char *sha1, int flag, void *cb_data)
 {
-	for_each_reflog_ent(logname, fsck_handle_reflog_ent, NULL);
+	for_each_reflog_ent(logname, fsck_handle_reflog_ent, (void *)logname);
 	return 0;
 }