fsck: unify object-name code

Commit 90cf590f53 (fsck: optionally show more helpful info for broken
links, 2016-07-17) added a system for decorating objects with names. The
code is split across builtin/fsck.c (which gives the initial names) and
fsck.c (which adds to the names as it traverses the object graph). This
leads to some duplication, where both sites have near-identical
describe_object() functions (the difference being that the one in
builtin/fsck.c uses a circular array of buffers to allow multiple calls
in a single printf).

Let's provide a unified object_name API for fsck. That lets us drop the
duplication, as well as making the interface boundaries more clear
(which will let us refactor the implementation more in a future patch).

We'll leave describe_object() in builtin/fsck.c as a thin wrapper around
the new API, as it relies on a static global to make its many callers a
bit shorter.

We'll also convert the bare add_decoration() calls in builtin/fsck.c to
put_object_name(). This fixes two minor bugs:

  1. We leak many small strings. add_decoration() has a last-one-wins
     approach: it updates the decoration to the new string and returns
     the old one. But we ignore the return value, leaking the old
     string. This is quite common to trigger, since we look at reflogs:
     the tip of any ref will be described both by looking at the actual
     ref, as well as the latest reflog entry. So we'd always end up
     leaking one of those strings.

  2. The last-one-wins approach gives us lousy names. For instance, we
     first look at all of the refs, and then all of the reflogs. So
     rather than seeing "refs/heads/master", we're likely to overwrite
     it with "HEAD@{12345678}". We're generally better off using the
     first name we find.

     And indeed, the test in t1450 expects this ugly HEAD@{} name. After
     this patch, we've switched to using fsck_put_object_name()'s
     first-one-wins semantics, and we output the more human-friendly
     "refs/tags/julius" (and the test is updated accordingly).

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

1 files changed, 13 insertions, 37 deletions

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 18403a9..237643c 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -52,24 +52,7 @@ static int name_objects;
 
 static const char *describe_object(struct object *obj)
 {
-	static struct strbuf bufs[] = {
-		STRBUF_INIT, STRBUF_INIT, STRBUF_INIT, STRBUF_INIT
-	};
-	static int b = 0;
-	struct strbuf *buf;
-	char *name = NULL;
-
-	if (name_objects)
-		name = lookup_decoration(fsck_walk_options.object_names, obj);
-
-	buf = bufs + b;
-	b = (b + 1) % ARRAY_SIZE(bufs);
-	strbuf_reset(buf);
-	strbuf_addstr(buf, oid_to_hex(&obj->oid));
-	if (name)
-		strbuf_addf(buf, " (%s)", name);
-
-	return buf->buf;
+	return fsck_describe_object(&fsck_walk_options, obj);
 }
 
 static const char *printable_type(struct object *obj)
@@ -499,10 +482,10 @@ static void fsck_handle_reflog_oid(const char *refname, struct object_id *oid,
 	if (!is_null_oid(oid)) {
 		obj = lookup_object(the_repository, oid);
 		if (obj && (obj->flags & HAS_OBJ)) {
-			if (timestamp && name_objects)
-				add_decoration(fsck_walk_options.object_names,
-					obj,
-					xstrfmt("%s@{%"PRItime"}", refname, timestamp));
+			if (timestamp)
+				fsck_put_object_name(&fsck_walk_options, obj,
+						     "%s@{%"PRItime"}",
+						     refname, timestamp);
 			obj->flags |= USED;
 			mark_object_reachable(obj);
 		} else if (!is_promisor_object(oid)) {
@@ -566,9 +549,8 @@ static int fsck_handle_ref(const char *refname, const struct object_id *oid,
 	}
 	default_refs++;
 	obj->flags |= USED;
-	if (name_objects)
-		add_decoration(fsck_walk_options.object_names,
-			obj, xstrdup(refname));
+	fsck_put_object_name(&fsck_walk_options,
+			     obj, "%s", refname);
 	mark_object_reachable(obj);
 
 	return 0;
@@ -742,9 +724,7 @@ static int fsck_cache_tree(struct cache_tree *it)
 			return 1;
 		}
 		obj->flags |= USED;
-		if (name_objects)
-			add_decoration(fsck_walk_options.object_names,
-				obj, xstrdup(":"));
+		fsck_put_object_name(&fsck_walk_options, obj, ":");
 		mark_object_reachable(obj);
 		if (obj->type != OBJ_TREE)
 			err |= objerror(obj, _("non-tree in cache-tree"));
@@ -830,8 +810,7 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 	}
 
 	if (name_objects)
-		fsck_walk_options.object_names =
-			xcalloc(1, sizeof(struct decoration));
+		fsck_enable_object_names(&fsck_walk_options);
 
 	git_config(fsck_config, NULL);
 
@@ -890,9 +869,8 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 			}
 
 			obj->flags |= USED;
-			if (name_objects)
-				add_decoration(fsck_walk_options.object_names,
-					obj, xstrdup(arg));
+			fsck_put_object_name(&fsck_walk_options, obj,
+					     "%s", arg);
 			mark_object_reachable(obj);
 			continue;
 		}
@@ -928,10 +906,8 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 				continue;
 			obj = &blob->object;
 			obj->flags |= USED;
-			if (name_objects)
-				add_decoration(fsck_walk_options.object_names,
-					obj,
-					xstrfmt(":%s", active_cache[i]->name));
+			fsck_put_object_name(&fsck_walk_options, obj,
+					     ":%s", active_cache[i]->name);
 			mark_object_reachable(obj);
 		}
 		if (active_cache_tree)