fsck: move typename() printing to its own function

When an object has a problem, we mention its type. But we do
so by feeding the result of typename() directly to
fprintf(). This is potentially dangerous because typename()
can return NULL for some type values (like OBJ_NONE).

It's doubtful that this can be triggered in practice with
the current code, so this is probably not fixing a bug. But
it future-proofs us against modifications that make things
like OBJ_NONE more likely (and gives future patches a
central point to handle them).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fsck.c

@@ -56,6 +56,17 @@ static const char *describe_object(struct object *obj)
 	return buf.buf;
 }
 
+static const char *printable_type(struct object *obj)
+{
+	const char *ret;
+
+	ret = typename(obj->type);
+	if (!ret)
+		ret = "unknown";
+
+	return ret;
+}
+
 static int fsck_config(const char *var, const char *value, void *cb)
 {
 	if (strcmp(var, "fsck.skiplist") == 0) {
@@ -83,7 +94,7 @@ static void objreport(struct object *obj, const char *msg_type,
 			const char *err)
 {
 	fprintf(stderr, "%s in %s %s: %s\n",
-		msg_type, typename(obj->type), describe_object(obj), err);
+		msg_type, printable_type(obj), describe_object(obj), err);
 }
 
 static int objerror(struct object *obj, const char *err)
@@ -114,7 +125,7 @@ static int mark_object(struct object *obj, int type, void *data, struct fsck_opt
 	if (!obj) {
 		/* ... these references to parent->fld are safe here */
 		printf("broken link from %7s %s\n",
-			   typename(parent->type), describe_object(parent));
+			   printable_type(parent), describe_object(parent));
 		printf("broken link from %7s %s\n",
 			   (type == OBJ_ANY ? "unknown" : typename(type)), "unknown");
 		errors_found |= ERROR_REACHABLE;
@@ -131,9 +142,9 @@ static int mark_object(struct object *obj, int type, void *data, struct fsck_opt
 	if (!(obj->flags & HAS_OBJ)) {
 		if (parent && !has_object_file(&obj->oid)) {
 			printf("broken link from %7s %s\n",
-				 typename(parent->type), describe_object(parent));
+				 printable_type(parent), describe_object(parent));
 			printf("              to %7s %s\n",
-				 typename(obj->type), describe_object(obj));
+				 printable_type(obj), describe_object(obj));
 			errors_found |= ERROR_REACHABLE;
 		}
 		return 1;
@@ -205,7 +216,7 @@ static void check_reachable_object(struct object *obj)
 	if (!(obj->flags & HAS_OBJ)) {
 		if (has_sha1_pack(obj->oid.hash))
 			return; /* it is in pack - forget about it */
-		printf("missing %s %s\n", typename(obj->type),
+		printf("missing %s %s\n", printable_type(obj),
 			describe_object(obj));
 		errors_found |= ERROR_REACHABLE;
 		return;
@@ -231,7 +242,7 @@ static void check_unreachable_object(struct object *obj)
 	 * since this is something that is prunable.
 	 */
 	if (show_unreachable) {
-		printf("unreachable %s %s\n", typename(obj->type),
+		printf("unreachable %s %s\n", printable_type(obj),
 			describe_object(obj));
 		return;
 	}
@@ -250,7 +261,7 @@ static void check_unreachable_object(struct object *obj)
 	 */
 	if (!obj->used) {
 		if (show_dangling)
-			printf("dangling %s %s\n", typename(obj->type),
+			printf("dangling %s %s\n", printable_type(obj),
 			       describe_object(obj));
 		if (write_lost_and_found) {
 			char *filename = git_pathdup("lost-found/%s/%s",
@@ -324,7 +335,7 @@ static int fsck_obj(struct object *obj)
 
 	if (verbose)
 		fprintf(stderr, "Checking %s %s\n",
-			typename(obj->type), describe_object(obj));
+			printable_type(obj), describe_object(obj));
 
 	if (fsck_walk(obj, NULL, &fsck_obj_options))
 		objerror(obj, "broken links");
@@ -350,7 +361,7 @@ static int fsck_obj(struct object *obj)
 		struct tag *tag = (struct tag *) obj;
 
 		if (show_tags && tag->tagged) {
-			printf("tagged %s %s", typename(tag->tagged->type),
+			printf("tagged %s %s", printable_type(tag->tagged),
 				describe_object(tag->tagged));
 			printf(" (%s) in %s\n", tag->tag,
 				describe_object(&tag->object));