use get_tagged_oid()

Avoid derefencing ->tagged without checking for NULL by using the
convenience wrapper for getting the ID of the tagged object.  It die()s
when encountering a broken tag instead of segfaulting.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/describe.c

@@ -313,7 +313,7 @@ static void describe_commit(struct object_id *oid, struct strbuf *dst)
 		 */
 		append_name(n, dst);
 		if (longformat)
-			append_suffix(0, n->tag ? &n->tag->tagged->oid : oid, dst);
+			append_suffix(0, n->tag ? get_tagged_oid(n->tag) : oid, dst);
 		if (suffix)
 			strbuf_addstr(dst, suffix);
 		return;

builtin/log.c

@@ -627,6 +627,7 @@ int cmd_show(int argc, const char **argv, const char *prefix)
 			break;
 		case OBJ_TAG: {
 			struct tag *t = (struct tag *)o;
+			struct object_id *oid = get_tagged_oid(t);
 
 			if (rev.shown_one)
 				putchar('\n');
@@ -638,10 +639,10 @@ int cmd_show(int argc, const char **argv, const char *prefix)
 			rev.shown_one = 1;
 			if (ret)
 				break;
-			o = parse_object(the_repository, &t->tagged->oid);
+			o = parse_object(the_repository, oid);
 			if (!o)
 				ret = error(_("could not read object %s"),
-					    oid_to_hex(&t->tagged->oid));
+					    oid_to_hex(oid));
 			objects[i].item = o;
 			i--;
 			break;

builtin/replace.c

@@ -421,7 +421,7 @@ static int check_one_mergetag(struct commit *commit,
 		if (get_oid(mergetag_data->argv[i], &oid) < 0)
 			return error(_("not a valid object name: '%s'"),
 				     mergetag_data->argv[i]);
-		if (oideq(&tag->tagged->oid, &oid))
+		if (oideq(get_tagged_oid(tag), &oid))
 			return 0; /* found */
 	}
 

packfile.c

@@ -2139,7 +2139,7 @@ static int add_promisor_object(const struct object_id *oid,
 			oidset_insert(set, &parents->item->object.oid);
 	} else if (obj->type == OBJ_TAG) {
 		struct tag *tag = (struct tag *) obj;
-		oidset_insert(set, &tag->tagged->oid);
+		oidset_insert(set, get_tagged_oid(tag));
 	}
 	return 0;
 }

ref-filter.c

@@ -1766,7 +1766,7 @@ static int populate_value(struct ref_array_item *ref, struct strbuf *err)
 	 * If it is a tag object, see if we use a value that derefs
 	 * the object, and if we do grab the object it refers to.
 	 */
-	oi_deref.oid = ((struct tag *)obj)->tagged->oid;
+	oi_deref.oid = *get_tagged_oid((struct tag *)obj);
 
 	/*
 	 * NEEDSWORK: This derefs tag only once, which
@@ -1997,7 +1997,7 @@ static const struct object_id *match_points_at(struct oid_array *points_at,
 	if (!obj)
 		die(_("malformed object at '%s'"), refname);
 	if (obj->type == OBJ_TAG)
-		tagged_oid = &((struct tag *)obj)->tagged->oid;
+		tagged_oid = get_tagged_oid((struct tag *)obj);
 	if (tagged_oid && oid_array_lookup(points_at, tagged_oid) >= 0)
 		return tagged_oid;
 	return NULL;