Merge branch 'jk/cleanup-object-parsing-and-fsck'

Crufty code and logic accumulated over time around the object
parsing and low-level object access used in "git fsck" have been
cleaned up.

* jk/cleanup-object-parsing-and-fsck: (23 commits)
  fsck: accept an oid instead of a "struct tree" for fsck_tree()
  fsck: accept an oid instead of a "struct commit" for fsck_commit()
  fsck: accept an oid instead of a "struct tag" for fsck_tag()
  fsck: rename vague "oid" local variables
  fsck: don't require an object struct in verify_headers()
  fsck: don't require an object struct for fsck_ident()
  fsck: drop blob struct from fsck_finish()
  fsck: accept an oid instead of a "struct blob" for fsck_blob()
  fsck: don't require an object struct for report()
  fsck: only require an oid for skiplist functions
  fsck: only provide oid/type in fsck_error callback
  fsck: don't require object structs for display functions
  fsck: use oids rather than objects for object_name API
  fsck_describe_object(): build on our get_object_name() primitive
  fsck: unify object-name code
  fsck: require an actual buffer for non-blobs
  fsck: stop checking tag->tagged
  fsck: stop checking commit->parent counts
  fsck: stop checking commit->tree value
  commit, tag: don't set parsed bit for parse failures
  ...

9 files changed, 312 insertions, 302 deletions

diff --git a/builtin/fsck.c b/builtin/fsck.c
index 18403a94fa..8d13794b14 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -50,40 +50,20 @@ static int name_objects;
 #define ERROR_REFS 010
 #define ERROR_COMMIT_GRAPH 020
 
-static const char *describe_object(struct object *obj)
+static const char *describe_object(const struct object_id *oid)
 {
-	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, oid);
 }
 
-static const char *printable_type(struct object *obj)
+static const char *printable_type(const struct object_id *oid,
+				  enum object_type type)
 {
 	const char *ret;
 
-	if (obj->type == OBJ_NONE) {
-		enum object_type type = oid_object_info(the_repository,
-							&obj->oid, NULL);
-		if (type > 0)
-			object_as_type(the_repository, obj, type, 0);
-	}
+	if (type == OBJ_NONE)
+		type = oid_object_info(the_repository, oid, NULL);
 
-	ret = type_name(obj->type);
+	ret = type_name(type);
 	if (!ret)
 		ret = _("unknown");
 
@@ -118,26 +98,32 @@ static int objerror(struct object *obj, const char *err)
 	errors_found |= ERROR_OBJECT;
 	/* TRANSLATORS: e.g. error in tree 01bfda: <more explanation> */
 	fprintf_ln(stderr, _("error in %s %s: %s"),
-		   printable_type(obj), describe_object(obj), err);
+		   printable_type(&obj->oid, obj->type),
+		   describe_object(&obj->oid), err);
 	return -1;
 }
 
 static int fsck_error_func(struct fsck_options *o,
-	struct object *obj, int type, const char *message)
+			   const struct object_id *oid,
+			   enum object_type object_type,
+			   int msg_type, const char *message)
 {
-	switch (type) {
+	switch (msg_type) {
 	case FSCK_WARN:
 		/* TRANSLATORS: e.g. warning in tree 01bfda: <more explanation> */
 		fprintf_ln(stderr, _("warning in %s %s: %s"),
-			   printable_type(obj), describe_object(obj), message);
+			   printable_type(oid, object_type),
+			   describe_object(oid), message);
 		return 0;
 	case FSCK_ERROR:
 		/* TRANSLATORS: e.g. error in tree 01bfda: <more explanation> */
 		fprintf_ln(stderr, _("error in %s %s: %s"),
-			   printable_type(obj), describe_object(obj), message);
+			   printable_type(oid, object_type),
+			   describe_object(oid), message);
 		return 1;
 	default:
-		BUG("%d (FSCK_IGNORE?) should never trigger this callback", type);
+		BUG("%d (FSCK_IGNORE?) should never trigger this callback",
+		    msg_type);
 	}
 }
 
@@ -155,7 +141,8 @@ 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_ln(_("broken link from %7s %s"),
-			  printable_type(parent), describe_object(parent));
+			  printable_type(&parent->oid, parent->type),
+			  describe_object(&parent->oid));
 		printf_ln(_("broken link from %7s %s"),
 			  (type == OBJ_ANY ? _("unknown") : type_name(type)),
 			  _("unknown"));
@@ -183,10 +170,10 @@ static int mark_object(struct object *obj, int type, void *data, struct fsck_opt
 		if (parent && !has_object_file(&obj->oid)) {
 			printf_ln(_("broken link from %7s %s\n"
 				    "              to %7s %s"),
-				  printable_type(parent),
-				  describe_object(parent),
-				  printable_type(obj),
-				  describe_object(obj));
+				  printable_type(&parent->oid, parent->type),
+				  describe_object(&parent->oid),
+				  printable_type(&obj->oid, obj->type),
+				  describe_object(&obj->oid));
 			errors_found |= ERROR_REACHABLE;
 		}
 		return 1;
@@ -292,8 +279,9 @@ static void check_reachable_object(struct object *obj)
 			return;
 		if (has_object_pack(&obj->oid))
 			return; /* it is in pack - forget about it */
-		printf_ln(_("missing %s %s"), printable_type(obj),
-			  describe_object(obj));
+		printf_ln(_("missing %s %s"),
+			  printable_type(&obj->oid, obj->type),
+			  describe_object(&obj->oid));
 		errors_found |= ERROR_REACHABLE;
 		return;
 	}
@@ -318,8 +306,9 @@ static void check_unreachable_object(struct object *obj)
 	 * since this is something that is prunable.
 	 */
 	if (show_unreachable) {
-		printf_ln(_("unreachable %s %s"), printable_type(obj),
-			  describe_object(obj));
+		printf_ln(_("unreachable %s %s"),
+			  printable_type(&obj->oid, obj->type),
+			  describe_object(&obj->oid));
 		return;
 	}
 
@@ -337,12 +326,13 @@ static void check_unreachable_object(struct object *obj)
 	 */
 	if (!(obj->flags & USED)) {
 		if (show_dangling)
-			printf_ln(_("dangling %s %s"), printable_type(obj),
-				  describe_object(obj));
+			printf_ln(_("dangling %s %s"),
+				  printable_type(&obj->oid, obj->type),
+				  describe_object(&obj->oid));
 		if (write_lost_and_found) {
 			char *filename = git_pathdup("lost-found/%s/%s",
 				obj->type == OBJ_COMMIT ? "commit" : "other",
-				describe_object(obj));
+				describe_object(&obj->oid));
 			FILE *f;
 
 			if (safe_create_leading_directories_const(filename)) {
@@ -355,7 +345,7 @@ static void check_unreachable_object(struct object *obj)
 				if (stream_blob_to_fd(fileno(f), &obj->oid, NULL, 1))
 					die_errno(_("could not write '%s'"), filename);
 			} else
-				fprintf(f, "%s\n", describe_object(obj));
+				fprintf(f, "%s\n", describe_object(&obj->oid));
 			if (fclose(f))
 				die_errno(_("could not finish '%s'"),
 					  filename);
@@ -374,7 +364,7 @@ static void check_unreachable_object(struct object *obj)
 static void check_object(struct object *obj)
 {
 	if (verbose)
-		fprintf_ln(stderr, _("Checking %s"), describe_object(obj));
+		fprintf_ln(stderr, _("Checking %s"), describe_object(&obj->oid));
 
 	if (obj->flags & REACHABLE)
 		check_reachable_object(obj);
@@ -432,7 +422,8 @@ static int fsck_obj(struct object *obj, void *buffer, unsigned long size)
 
 	if (verbose)
 		fprintf_ln(stderr, _("Checking %s %s"),
-			   printable_type(obj), describe_object(obj));
+			   printable_type(&obj->oid, obj->type),
+			   describe_object(&obj->oid));
 
 	if (fsck_walk(obj, NULL, &fsck_obj_options))
 		objerror(obj, _("broken links"));
@@ -445,7 +436,7 @@ static int fsck_obj(struct object *obj, void *buffer, unsigned long size)
 
 		if (!commit->parents && show_root)
 			printf_ln(_("root %s"),
-				  describe_object(&commit->object));
+				  describe_object(&commit->object.oid));
 	}
 
 	if (obj->type == OBJ_TAG) {
@@ -453,10 +444,10 @@ static int fsck_obj(struct object *obj, void *buffer, unsigned long size)
 
 		if (show_tags && tag->tagged) {
 			printf_ln(_("tagged %s %s (%s) in %s"),
-				  printable_type(tag->tagged),
-				  describe_object(tag->tagged),
+				  printable_type(&tag->tagged->oid, tag->tagged->type),
+				  describe_object(&tag->tagged->oid),
 				  tag->tag,
-				  describe_object(&tag->object));
+				  describe_object(&tag->object.oid));
 		}
 	}
 
@@ -499,10 +490,10 @@ 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, oid,
+						     "%s@{%"PRItime"}",
+						     refname, timestamp);
 			obj->flags |= USED;
 			mark_object_reachable(obj);
 		} else if (!is_promisor_object(oid)) {
@@ -566,9 +557,8 @@ 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,
+			     oid, "%s", refname);
 	mark_object_reachable(obj);
 
 	return 0;
@@ -742,9 +732,7 @@ 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, &it->oid, ":");
 		mark_object_reachable(obj);
 		if (obj->type != OBJ_TREE)
 			err |= objerror(obj, _("non-tree in cache-tree"));
@@ -830,8 +818,7 @@ 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 +877,8 @@ 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, &oid,
+					     "%s", arg);
 			mark_object_reachable(obj);
 			continue;
 		}
@@ -928,10 +914,8 @@ 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->oid,
+					     ":%s", active_cache[i]->name);
 			mark_object_reachable(obj);
 		}
 		if (active_cache_tree)
diff --git a/commit-graph.c b/commit-graph.c
index 0aea7b2ae5..a0f868522b 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -858,9 +858,6 @@ static void write_graph_chunk_data(struct hashfile *f, int hash_len,
 			die(_("unable to parse commit %s"),
 				oid_to_hex(&(*list)->object.oid));
 		tree = get_commit_tree_oid(*list);
-		if (!tree)
-			die(_("unable to get tree for %s"),
-				oid_to_hex(&(*list)->object.oid));
 		hashwrite(f, tree->hash, hash_len);
 
 		parent = (*list)->parents;
diff --git a/commit.c b/commit.c
index 52036bc90f..434ec030d6 100644
--- a/commit.c
+++ b/commit.c
@@ -402,10 +402,22 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
 	struct commit_graft *graft;
 	const int tree_entry_len = the_hash_algo->hexsz + 5;
 	const int parent_entry_len = the_hash_algo->hexsz + 7;
+	struct tree *tree;
 
 	if (item->object.parsed)
 		return 0;
-	item->object.parsed = 1;
+
+	if (item->parents) {
+		/*
+		 * Presumably this is leftover from an earlier failed parse;
+		 * clear it out in preparation for us re-parsing (we'll hit the
+		 * same error, but that's good, since it lets our caller know
+		 * the result cannot be trusted.
+		 */
+		free_commit_list(item->parents);
+		item->parents = NULL;
+	}
+
 	tail += size;
 	if (tail <= bufptr + tree_entry_len + 1 || memcmp(bufptr, "tree ", 5) ||
 			bufptr[tree_entry_len] != '\n')
@@ -413,7 +425,12 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
 	if (get_oid_hex(bufptr + 5, &parent) < 0)
 		return error("bad tree pointer in commit %s",
 			     oid_to_hex(&item->object.oid));
-	set_commit_tree(item, lookup_tree(r, &parent));
+	tree = lookup_tree(r, &parent);
+	if (!tree)
+		return error("bad tree pointer %s in commit %s",
+			     oid_to_hex(&parent),
+			     oid_to_hex(&item->object.oid));
+	set_commit_tree(item, tree);
 	bufptr += tree_entry_len + 1; /* "tree " + "hex sha1" + "\n" */
 	pptr = &item->parents;
 
@@ -433,8 +450,11 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
 		if (graft && (graft->nr_parent < 0 || grafts_replace_parents))
 			continue;
 		new_parent = lookup_commit(r, &parent);
-		if (new_parent)
-			pptr = &commit_list_insert(new_parent, pptr)->next;
+		if (!new_parent)
+			return error("bad parent %s in commit %s",
+				     oid_to_hex(&parent),
+				     oid_to_hex(&item->object.oid));
+		pptr = &commit_list_insert(new_parent, pptr)->next;
 	}
 	if (graft) {
 		int i;
@@ -443,7 +463,9 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
 			new_parent = lookup_commit(r,
 						   &graft->parent[i]);
 			if (!new_parent)
-				continue;
+				return error("bad graft parent %s in commit %s",
+					     oid_to_hex(&graft->parent[i]),
+					     oid_to_hex(&item->object.oid));
 			pptr = &commit_list_insert(new_parent, pptr)->next;
 		}
 	}
@@ -452,6 +474,7 @@ int parse_commit_buffer(struct repository *r, struct commit *item, const void *b
 	if (check_graph)
 		load_commit_graph_info(r, item);
 
+	item->object.parsed = 1;
 	return 0;
 }
 
diff --git a/fsck.c b/fsck.c
index cdb7d8db03..ac4ba4c8e8 100644
--- a/fsck.c
+++ b/fsck.c
@@ -43,21 +43,17 @@ static struct oidset gitmodules_done = OIDSET_INIT;
 	FUNC(MISSING_AUTHOR, ERROR) \
 	FUNC(MISSING_COMMITTER, ERROR) \
 	FUNC(MISSING_EMAIL, ERROR) \
-	FUNC(MISSING_GRAFT, ERROR) \
 	FUNC(MISSING_NAME_BEFORE_EMAIL, ERROR) \
 	FUNC(MISSING_OBJECT, ERROR) \
-	FUNC(MISSING_PARENT, ERROR) \
 	FUNC(MISSING_SPACE_BEFORE_DATE, ERROR) \
 	FUNC(MISSING_SPACE_BEFORE_EMAIL, ERROR) \
 	FUNC(MISSING_TAG, ERROR) \
 	FUNC(MISSING_TAG_ENTRY, ERROR) \
-	FUNC(MISSING_TAG_OBJECT, ERROR) \
 	FUNC(MISSING_TREE, ERROR) \
 	FUNC(MISSING_TREE_OBJECT, ERROR) \
 	FUNC(MISSING_TYPE, ERROR) \
 	FUNC(MISSING_TYPE_ENTRY, ERROR) \
 	FUNC(MULTIPLE_AUTHORS, ERROR) \
-	FUNC(TAG_OBJECT_NOT_TAG, ERROR) \
 	FUNC(TREE_NOT_SORTED, ERROR) \
 	FUNC(UNKNOWN_TYPE, ERROR) \
 	FUNC(ZERO_PADDED_DATE, ERROR) \
@@ -281,14 +277,16 @@ static void append_msg_id(struct strbuf *sb, const char *msg_id)
 	strbuf_addstr(sb, ": ");
 }
 
-static int object_on_skiplist(struct fsck_options *opts, struct object *obj)
+static int object_on_skiplist(struct fsck_options *opts,
+			      const struct object_id *oid)
 {
-	return opts && obj && oidset_contains(&opts->skiplist, &obj->oid);
+	return opts && oid && oidset_contains(&opts->skiplist, oid);
 }
 
-__attribute__((format (printf, 4, 5)))
-static int report(struct fsck_options *options, struct object *object,
-	enum fsck_msg_id id, const char *fmt, ...)
+__attribute__((format (printf, 5, 6)))
+static int report(struct fsck_options *options,
+		  const struct object_id *oid, enum object_type object_type,
+		  enum fsck_msg_id id, const char *fmt, ...)
 {
 	va_list ap;
 	struct strbuf sb = STRBUF_INIT;
@@ -297,7 +295,7 @@ static int report(struct fsck_options *options, struct object *object,
 	if (msg_type == FSCK_IGNORE)
 		return 0;
 
-	if (object_on_skiplist(options, object))
+	if (object_on_skiplist(options, oid))
 		return 0;
 
 	if (msg_type == FSCK_FATAL)
@@ -309,49 +307,71 @@ static int report(struct fsck_options *options, struct object *object,
 
 	va_start(ap, fmt);
 	strbuf_vaddf(&sb, fmt, ap);
-	result = options->error_func(options, object, msg_type, sb.buf);
+	result = options->error_func(options, oid, object_type,
+				     msg_type, sb.buf);
 	strbuf_release(&sb);
 	va_end(ap);
 
 	return result;
 }
 
-static char *get_object_name(struct fsck_options *options, struct object *obj)
+void fsck_enable_object_names(struct fsck_options *options)
 {
 	if (!options->object_names)
+		options->object_names = kh_init_oid_map();
+}
+
+const char *fsck_get_object_name(struct fsck_options *options,
+				 const struct object_id *oid)
+{
+	khiter_t pos;
+	if (!options->object_names)
+		return NULL;
+	pos = kh_get_oid_map(options->object_names, *oid);
+	if (pos >= kh_end(options->object_names))
 		return NULL;
-	return lookup_decoration(options->object_names, obj);
+	return kh_value(options->object_names, pos);
 }
 
-static void put_object_name(struct fsck_options *options, struct object *obj,
-	const char *fmt, ...)
+void fsck_put_object_name(struct fsck_options *options,
+			  const struct object_id *oid,
+			  const char *fmt, ...)
 {
 	va_list ap;
 	struct strbuf buf = STRBUF_INIT;
-	char *existing;
+	khiter_t pos;
+	int hashret;
 
 	if (!options->object_names)
 		return;
-	existing = lookup_decoration(options->object_names, obj);
-	if (existing)
+
+	pos = kh_put_oid_map(options->object_names, *oid, &hashret);
+	if (!hashret)
 		return;
 	va_start(ap, fmt);
 	strbuf_vaddf(&buf, fmt, ap);
-	add_decoration(options->object_names, obj, strbuf_detach(&buf, NULL));
+	kh_value(options->object_names, pos) = strbuf_detach(&buf, NULL);
 	va_end(ap);
 }
 
-static const char *describe_object(struct fsck_options *o, struct object *obj)
+const char *fsck_describe_object(struct fsck_options *options,
+				 const struct object_id *oid)
 {
-	static struct strbuf buf = STRBUF_INIT;
-	char *name;
-
-	strbuf_reset(&buf);
-	strbuf_addstr(&buf, oid_to_hex(&obj->oid));
-	if (o->object_names && (name = lookup_decoration(o->object_names, obj)))
-		strbuf_addf(&buf, " (%s)", name);
+	static struct strbuf bufs[] = {
+		STRBUF_INIT, STRBUF_INIT, STRBUF_INIT, STRBUF_INIT
+	};
+	static int b = 0;
+	struct strbuf *buf;
+	const char *name = fsck_get_object_name(options, oid);
+
+	buf = bufs + b;
+	b = (b + 1) % ARRAY_SIZE(bufs);
+	strbuf_reset(buf);
+	strbuf_addstr(buf, oid_to_hex(oid));
+	if (name)
+		strbuf_addf(buf, " (%s)", name);
 
-	return buf.buf;
+	return buf->buf;
 }
 
 static int fsck_walk_tree(struct tree *tree, void *data, struct fsck_options *options)
@@ -364,7 +384,7 @@ static int fsck_walk_tree(struct tree *tree, void *data, struct fsck_options *op
 	if (parse_tree(tree))
 		return -1;
 
-	name = get_object_name(options, &tree->object);
+	name = fsck_get_object_name(options, &tree->object.oid);
 	if (init_tree_desc_gently(&desc, tree->buffer, tree->size))
 		return -1;
 	while (tree_entry_gently(&desc, &entry)) {
@@ -377,20 +397,21 @@ static int fsck_walk_tree(struct tree *tree, void *data, struct fsck_options *op
 		if (S_ISDIR(entry.mode)) {
 			obj = (struct object *)lookup_tree(the_repository, &entry.oid);
 			if (name && obj)
-				put_object_name(options, obj, "%s%s/", name,
-					entry.path);
+				fsck_put_object_name(options, &entry.oid, "%s%s/",
+						     name, entry.path);
 			result = options->walk(obj, OBJ_TREE, data, options);
 		}
 		else if (S_ISREG(entry.mode) || S_ISLNK(entry.mode)) {
 			obj = (struct object *)lookup_blob(the_repository, &entry.oid);
 			if (name && obj)
-				put_object_name(options, obj, "%s%s", name,
-					entry.path);
+				fsck_put_object_name(options, &entry.oid, "%s%s",
+						     name, entry.path);
 			result = options->walk(obj, OBJ_BLOB, data, options);
 		}
 		else {
 			result = error("in tree %s: entry %s has bad mode %.6o",
-					describe_object(options, &tree->object), entry.path, entry.mode);
+				       fsck_describe_object(options, &tree->object.oid),
+				       entry.path, entry.mode);
 		}
 		if (result < 0)
 			return result;
@@ -411,10 +432,10 @@ static int fsck_walk_commit(struct commit *commit, void *data, struct fsck_optio
 	if (parse_commit(commit))
 		return -1;
 
-	name = get_object_name(options, &commit->object);
+	name = fsck_get_object_name(options, &commit->object.oid);
 	if (name)
-		put_object_name(options, &get_commit_tree(commit)->object,
-				"%s:", name);
+		fsck_put_object_name(options, get_commit_tree_oid(commit),
+				     "%s:", name);
 
 	result = options->walk((struct object *)get_commit_tree(commit),
 			       OBJ_TREE, data, options);
@@ -442,16 +463,17 @@ static int fsck_walk_commit(struct commit *commit, void *data, struct fsck_optio
 
 	while (parents) {
 		if (name) {
-			struct object *obj = &parents->item->object;
+			struct object_id *oid = &parents->item->object.oid;
 
 			if (counter++)
-				put_object_name(options, obj, "%s^%d",
-					name, counter);
+				fsck_put_object_name(options, oid, "%s^%d",
+						     name, counter);
 			else if (generation > 0)
-				put_object_name(options, obj, "%.*s~%d",
-					name_prefix_len, name, generation + 1);
+				fsck_put_object_name(options, oid, "%.*s~%d",
+						     name_prefix_len, name,
+						     generation + 1);
 			else
-				put_object_name(options, obj, "%s^", name);
+				fsck_put_object_name(options, oid, "%s^", name);
 		}
 		result = options->walk((struct object *)parents->item, OBJ_COMMIT, data, options);
 		if (result < 0)
@@ -465,12 +487,12 @@ static int fsck_walk_commit(struct commit *commit, void *data, struct fsck_optio
 
 static int fsck_walk_tag(struct tag *tag, void *data, struct fsck_options *options)
 {
-	char *name = get_object_name(options, &tag->object);
+	const char *name = fsck_get_object_name(options, &tag->object.oid);
 
 	if (parse_tag(tag))
 		return -1;
 	if (name)
-		put_object_name(options, tag->tagged, "%s", name);
+		fsck_put_object_name(options, &tag->tagged->oid, "%s", name);
 	return options->walk(tag->tagged, OBJ_ANY, data, options);
 }
 
@@ -492,7 +514,8 @@ int fsck_walk(struct object *obj, void *data, struct fsck_options *options)
 	case OBJ_TAG:
 		return fsck_walk_tag((struct tag *)obj, data, options);
 	default:
-		error("Unknown object type for %s", describe_object(options, obj));
+		error("Unknown object type for %s",
+		      fsck_describe_object(options, &obj->oid));
 		return -1;
 	}
 }
@@ -543,7 +566,9 @@ static int verify_ordered(unsigned mode1, const char *name1, unsigned mode2, con
 	return c1 < c2 ? 0 : TREE_UNORDERED;
 }
 
-static int fsck_tree(struct tree *item, struct fsck_options *options)
+static int fsck_tree(const struct object_id *oid,
+		     const char *buffer, unsigned long size,
+		     struct fsck_options *options)
 {
 	int retval = 0;
 	int has_null_sha1 = 0;
@@ -560,8 +585,8 @@ static int fsck_tree(struct tree *item, struct fsck_options *options)
 	unsigned o_mode;
 	const char *o_name;
 
-	if (init_tree_desc_gently(&desc, item->buffer, item->size)) {
-		retval += report(options, &item->object, FSCK_MSG_BAD_TREE, "cannot be parsed as a tree");
+	if (init_tree_desc_gently(&desc, buffer, size)) {
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_BAD_TREE, "cannot be parsed as a tree");
 		return retval;
 	}
 
@@ -587,13 +612,14 @@ static int fsck_tree(struct tree *item, struct fsck_options *options)
 			if (!S_ISLNK(mode))
 				oidset_insert(&gitmodules_found, oid);
 			else
-				retval += report(options, &item->object,
+				retval += report(options,
+						 oid, OBJ_TREE,
 						 FSCK_MSG_GITMODULES_SYMLINK,
 						 ".gitmodules is a symbolic link");
 		}
 
 		if (update_tree_entry_gently(&desc)) {
-			retval += report(options, &item->object, FSCK_MSG_BAD_TREE, "cannot be parsed as a tree");
+			retval += report(options, oid, OBJ_TREE, FSCK_MSG_BAD_TREE, "cannot be parsed as a tree");
 			break;
 		}
 
@@ -638,30 +664,31 @@ static int fsck_tree(struct tree *item, struct fsck_options *options)
 	}
 
 	if (has_null_sha1)
-		retval += report(options, &item->object, FSCK_MSG_NULL_SHA1, "contains entries pointing to null sha1");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_NULL_SHA1, "contains entries pointing to null sha1");
 	if (has_full_path)
-		retval += report(options, &item->object, FSCK_MSG_FULL_PATHNAME, "contains full pathnames");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_FULL_PATHNAME, "contains full pathnames");
 	if (has_empty_name)
-		retval += report(options, &item->object, FSCK_MSG_EMPTY_NAME, "contains empty pathname");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_EMPTY_NAME, "contains empty pathname");
 	if (has_dot)
-		retval += report(options, &item->object, FSCK_MSG_HAS_DOT, "contains '.'");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_HAS_DOT, "contains '.'");
 	if (has_dotdot)
-		retval += report(options, &item->object, FSCK_MSG_HAS_DOTDOT, "contains '..'");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_HAS_DOTDOT, "contains '..'");
 	if (has_dotgit)
-		retval += report(options, &item->object, FSCK_MSG_HAS_DOTGIT, "contains '.git'");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_HAS_DOTGIT, "contains '.git'");
 	if (has_zero_pad)
-		retval += report(options, &item->object, FSCK_MSG_ZERO_PADDED_FILEMODE, "contains zero-padded file modes");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_ZERO_PADDED_FILEMODE, "contains zero-padded file modes");
 	if (has_bad_modes)
-		retval += report(options, &item->object, FSCK_MSG_BAD_FILEMODE, "contains bad file modes");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_BAD_FILEMODE, "contains bad file modes");
 	if (has_dup_entries)
-		retval += report(options, &item->object, FSCK_MSG_DUPLICATE_ENTRIES, "contains duplicate file entries");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_DUPLICATE_ENTRIES, "contains duplicate file entries");
 	if (not_properly_sorted)
-		retval += report(options, &item->object, FSCK_MSG_TREE_NOT_SORTED, "not properly sorted");
+		retval += report(options, oid, OBJ_TREE, FSCK_MSG_TREE_NOT_SORTED, "not properly sorted");
 	return retval;
 }
 
 static int verify_headers(const void *data, unsigned long size,
-			  struct object *obj, struct fsck_options *options)
+			  const struct object_id *oid, enum object_type type,
+			  struct fsck_options *options)
 {
 	const char *buffer = (const char *)data;
 	unsigned long i;
@@ -669,7 +696,7 @@ static int verify_headers(const void *data, unsigned long size,
 	for (i = 0; i < size; i++) {
 		switch (buffer[i]) {
 		case '\0':
-			return report(options, obj,
+			return report(options, oid, type,
 				FSCK_MSG_NUL_IN_HEADER,
 				"unterminated header: NUL at offset %ld", i);
 		case '\n':
@@ -687,11 +714,13 @@ static int verify_headers(const void *data, unsigned long size,
 	if (size && buffer[size - 1] == '\n')
 		return 0;
 
-	return report(options, obj,
+	return report(options, oid, type,
 		FSCK_MSG_UNTERMINATED_HEADER, "unterminated header");
 }
 
-static int fsck_ident(const char **ident, struct object *obj, struct fsck_options *options)
+static int fsck_ident(const char **ident,
+		      const struct object_id *oid, enum object_type type,
+		      struct fsck_options *options)
 {
 	const char *p = *ident;
 	char *end;
@@ -701,28 +730,28 @@ static int fsck_ident(const char **ident, struct object *obj, struct fsck_option
 		(*ident)++;
 
 	if (*p == '<')
-		return report(options, obj, FSCK_MSG_MISSING_NAME_BEFORE_EMAIL, "invalid author/committer line - missing space before email");
+		return report(options, oid, type, FSCK_MSG_MISSING_NAME_BEFORE_EMAIL, "invalid author/committer line - missing space before email");
 	p += strcspn(p, "<>\n");
 	if (*p == '>')
-		return report(options, obj, FSCK_MSG_BAD_NAME, "invalid author/committer line - bad name");
+		return report(options, oid, type, FSCK_MSG_BAD_NAME, "invalid author/committer line - bad name");
 	if (*p != '<')
-		return report(options, obj, FSCK_MSG_MISSING_EMAIL, "invalid author/committer line - missing email");
+		return report(options, oid, type, FSCK_MSG_MISSING_EMAIL, "invalid author/committer line - missing email");
 	if (p[-1] != ' ')
-		return report(options, obj, FSCK_MSG_MISSING_SPACE_BEFORE_EMAIL, "invalid author/committer line - missing space before email");
+		return report(options, oid, type, FSCK_MSG_MISSING_SPACE_BEFORE_EMAIL, "invalid author/committer line - missing space before email");
 	p++;
 	p += strcspn(p, "<>\n");
 	if (*p != '>')
-		return report(options, obj, FSCK_MSG_BAD_EMAIL, "invalid author/committer line - bad email");
+		return report(options, oid, type, FSCK_MSG_BAD_EMAIL, "invalid author/committer line - bad email");
 	p++;
 	if (*p != ' ')
-		return report(options, obj, FSCK_MSG_MISSING_SPACE_BEFORE_DATE, "invalid author/committer line - missing space before date");
+		return report(options, oid, type, FSCK_MSG_MISSING_SPACE_BEFORE_DATE, "invalid author/committer line - missing space before date");
 	p++;
 	if (*p == '0' && p[1] != ' ')
-		return report(options, obj, FSCK_MSG_ZERO_PADDED_DATE, "invalid author/committer line - zero-padded date");
+		return report(options, oid, type, FSCK_MSG_ZERO_PADDED_DATE, "invalid author/committer line - zero-padded date");
 	if (date_overflows(parse_timestamp(p, &end, 10)))
-		return report(options, obj, FSCK_MSG_BAD_DATE_OVERFLOW, "invalid author/committer line - date causes integer overflow");
+		return report(options, oid, type, FSCK_MSG_BAD_DATE_OVERFLOW, "invalid author/committer line - date causes integer overflow");
 	if ((end == p || *end != ' '))
-		return report(options, obj, FSCK_MSG_BAD_DATE, "invalid author/committer line - bad date");
+		return report(options, oid, type, FSCK_MSG_BAD_DATE, "invalid author/committer line - bad date");
 	p = end + 1;
 	if ((*p != '+' && *p != '-') ||
 	    !isdigit(p[1]) ||
@@ -730,83 +759,60 @@ static int fsck_ident(const char **ident, struct object *obj, struct fsck_option
 	    !isdigit(p[3]) ||
 	    !isdigit(p[4]) ||
 	    (p[5] != '\n'))
-		return report(options, obj, FSCK_MSG_BAD_TIMEZONE, "invalid author/committer line - bad time zone");
+		return report(options, oid, type, FSCK_MSG_BAD_TIMEZONE, "invalid author/committer line - bad time zone");
 	p += 6;
 	return 0;
 }
 
-static int fsck_commit_buffer(struct commit *commit, const char *buffer,
-	unsigned long size, struct fsck_options *options)
+static int fsck_commit(const struct object_id *oid,
+		       const char *buffer, unsigned long size,
+		       struct fsck_options *options)
 {
-	struct object_id tree_oid, oid;
-	struct commit_graft *graft;
-	unsigned parent_count, parent_line_count = 0, author_count;
+	struct object_id tree_oid, parent_oid;
+	unsigned author_count;
 	int err;
 	const char *buffer_begin = buffer;
 	const char *p;
 
-	if (verify_headers(buffer, size, &commit->object, options))
+	if (verify_headers(buffer, size, oid, OBJ_COMMIT, options))
 		return -1;
 
 	if (!skip_prefix(buffer, "tree ", &buffer))
-		return report(options, &commit->object, FSCK_MSG_MISSING_TREE, "invalid format - expected 'tree' line");
+		return report(options, oid, OBJ_COMMIT, FSCK_MSG_MISSING_TREE, "invalid format - expected 'tree' line");
 	if (parse_oid_hex(buffer, &tree_oid, &p) || *p != '\n') {
-		err = report(options, &commit->object, FSCK_MSG_BAD_TREE_SHA1, "invalid 'tree' line format - bad sha1");
+		err = report(options, oid, OBJ_COMMIT, FSCK_MSG_BAD_TREE_SHA1, "invalid 'tree' line format - bad sha1");
 		if (err)
 			return err;
 	}
 	buffer = p + 1;
 	while (skip_prefix(buffer, "parent ", &buffer)) {
-		if (parse_oid_hex(buffer, &oid, &p) || *p != '\n') {
-			err = report(options, &commit->object, FSCK_MSG_BAD_PARENT_SHA1, "invalid 'parent' line format - bad sha1");
+		if (parse_oid_hex(buffer, &parent_oid, &p) || *p != '\n') {
+			err = report(options, oid, OBJ_COMMIT, FSCK_MSG_BAD_PARENT_SHA1, "invalid 'parent' line format - bad sha1");
 			if (err)
 				return err;
 		}
 		buffer = p + 1;
-		parent_line_count++;
-	}
-	graft = lookup_commit_graft(the_repository, &commit->object.oid);
-	parent_count = commit_list_count(commit->parents);
-	if (graft) {
-		if (graft->nr_parent == -1 && !parent_count)
-			; /* shallow commit */
-		else if (graft->nr_parent != parent_count) {
-			err = report(options, &commit->object, FSCK_MSG_MISSING_GRAFT, "graft objects missing");
-			if (err)
-				return err;
-		}
-	} else {
-		if (parent_count != parent_line_count) {
-			err = report(options, &commit->object, FSCK_MSG_MISSING_PARENT, "parent objects missing");
-			if (err)
-				return err;
-		}
 	}
 	author_count = 0;
 	while (skip_prefix(buffer, "author ", &buffer)) {
 		author_count++;
-		err = fsck_ident(&buffer, &commit->object, options);
+		err = fsck_ident(&buffer, oid, OBJ_COMMIT, options);
 		if (err)
 			return err;
 	}
 	if (author_count < 1)
-		err = report(options, &commit->object, FSCK_MSG_MISSING_AUTHOR, "invalid format - expected 'author' line");
+		err = report(options, oid, OBJ_COMMIT, FSCK_MSG_MISSING_AUTHOR, "invalid format - expected 'author' line");
 	else if (author_count > 1)
-		err = report(options, &commit->object, FSCK_MSG_MULTIPLE_AUTHORS, "invalid format - multiple 'author' lines");
+		err = report(options, oid, OBJ_COMMIT, FSCK_MSG_MULTIPLE_AUTHORS, "invalid format - multiple 'author' lines");
 	if (err)
 		return err;
 	if (!skip_prefix(buffer, "committer ", &buffer))
-		return report(options, &commit->object, FSCK_MSG_MISSING_COMMITTER, "invalid format - expected 'committer' line");
-	err = fsck_ident(&buffer, &commit->object, options);
+		return report(options, oid, OBJ_COMMIT, FSCK_MSG_MISSING_COMMITTER, "invalid format - expected 'committer' line");
+	err = fsck_ident(&buffer, oid, OBJ_COMMIT, options);
 	if (err)
 		return err;
-	if (!get_commit_tree(commit)) {
-		err = report(options, &commit->object, FSCK_MSG_BAD_TREE, "could not load commit's tree %s", oid_to_hex(&tree_oid));
-		if (err)
-			return err;
-	}
 	if (memchr(buffer_begin, '\0', size)) {
-		err = report(options, &commit->object, FSCK_MSG_NUL_IN_COMMIT,
+		err = report(options, oid, OBJ_COMMIT, FSCK_MSG_NUL_IN_COMMIT,
 			     "NUL byte in the commit object body");
 		if (err)
 			return err;
@@ -814,91 +820,60 @@ static int fsck_commit_buffer(struct commit *commit, const char *buffer,
 	return 0;
 }
 
-static int fsck_commit(struct commit *commit, const char *data,
-	unsigned long size, struct fsck_options *options)
-{
-	const char *buffer = data ?  data : get_commit_buffer(commit, &size);
-	int ret = fsck_commit_buffer(commit, buffer, size, options);
-	if (!data)
-		unuse_commit_buffer(commit, buffer);
-	return ret;
-}
-
-static int fsck_tag_buffer(struct tag *tag, const char *data,
-	unsigned long size, struct fsck_options *options)
+static int fsck_tag(const struct object_id *oid, const char *buffer,
+		    unsigned long size, struct fsck_options *options)
 {
-	struct object_id oid;
+	struct object_id tagged_oid;
 	int ret = 0;
-	const char *buffer;
-	char *to_free = NULL, *eol;
+	char *eol;
 	struct strbuf sb = STRBUF_INIT;
 	const char *p;
 
-	if (data)
-		buffer = data;
-	else {
-		enum object_type type;
-
-		buffer = to_free =
-			read_object_file(&tag->object.oid, &type, &size);
-		if (!buffer)
-			return report(options, &tag->object,
-				FSCK_MSG_MISSING_TAG_OBJECT,
-				"cannot read tag object");
-
-		if (type != OBJ_TAG) {
-			ret = report(options, &tag->object,
-				FSCK_MSG_TAG_OBJECT_NOT_TAG,
-				"expected tag got %s",
-			    type_name(type));
-			goto done;
-		}
-	}
-
-	ret = verify_headers(buffer, size, &tag->object, options);
+	ret = verify_headers(buffer, size, oid, OBJ_TAG, options);
 	if (ret)
 		goto done;
 
 	if (!skip_prefix(buffer, "object ", &buffer)) {
-		ret = report(options, &tag->object, FSCK_MSG_MISSING_OBJECT, "invalid format - expected 'object' line");
+		ret = report(options, oid, OBJ_TAG, FSCK_MSG_MISSING_OBJECT, "invalid format - expected 'object' line");
 		goto done;
 	}
-	if (parse_oid_hex(buffer, &oid, &p) || *p != '\n') {
-		ret = report(options, &tag->object, FSCK_MSG_BAD_OBJECT_SHA1, "invalid 'object' line format - bad sha1");
+	if (parse_oid_hex(buffer, &tagged_oid, &p) || *p != '\n') {
+		ret = report(options, oid, OBJ_TAG, FSCK_MSG_BAD_OBJECT_SHA1, "invalid 'object' line format - bad sha1");
 		if (ret)
 			goto done;
 	}
 	buffer = p + 1;
 
 	if (!skip_prefix(buffer, "type ", &buffer)) {
-		ret = report(options, &tag->object, FSCK_MSG_MISSING_TYPE_ENTRY, "invalid format - expected 'type' line");
+		ret = report(options, oid, OBJ_TAG, FSCK_MSG_MISSING_TYPE_ENTRY, "invalid format - expected 'type' line");
 		goto done;
 	}
 	eol = strchr(buffer, '\n');
 	if (!eol) {
-		ret = report(options, &tag->object, FSCK_MSG_MISSING_TYPE, "invalid format - unexpected end after 'type' line");
+		ret = report(options, oid, OBJ_TAG, FSCK_MSG_MISSING_TYPE, "invalid format - unexpected end after 'type' line");
 		goto done;
 	}
 	if (type_from_string_gently(buffer, eol - buffer, 1) < 0)
-		ret = report(options, &tag->object, FSCK_MSG_BAD_TYPE, "invalid 'type' value");
+		ret = report(options, oid, OBJ_TAG, FSCK_MSG_BAD_TYPE, "invalid 'type' value");
 	if (ret)
 		goto done;
 	buffer = eol + 1;
 
 	if (!skip_prefix(buffer, "tag ", &buffer)) {
-		ret = report(options, &tag->object, FSCK_MSG_MISSING_TAG_ENTRY, "invalid format - expected 'tag' line");
+		ret = report(options, oid, OBJ_TAG, FSCK_MSG_MISSING_TAG_ENTRY, "invalid format - expected 'tag' line");
 		goto done;
 	}
 	eol = strchr(buffer, '\n');
 	if (!eol) {
-		ret = report(options, &tag->object, FSCK_MSG_MISSING_TAG, "invalid format - unexpected end after 'type' line");
+		ret = report(options, oid, OBJ_TAG, FSCK_MSG_MISSING_TAG, "invalid format - unexpected end after 'type' line");
 		goto done;
 	}
 	strbuf_addf(&sb, "refs/tags/%.*s", (int)(eol - buffer), buffer);
 	if (check_refname_format(sb.buf, 0)) {
-		ret = report(options, &tag->object, FSCK_MSG_BAD_TAG_NAME,
-			   "invalid 'tag' name: %.*s",
-			   (int)(eol - buffer), buffer);
+		ret = report(options, oid, OBJ_TAG,
+			     FSCK_MSG_BAD_TAG_NAME,
+			     "invalid 'tag' name: %.*s",
+			     (int)(eol - buffer), buffer);
 		if (ret)
 			goto done;
 	}
@@ -906,32 +881,20 @@ static int fsck_tag_buffer(struct tag *tag, const char *data,
 
 	if (!skip_prefix(buffer, "tagger ", &buffer)) {
 		/* early tags do not contain 'tagger' lines; warn only */
-		ret = report(options, &tag->object, FSCK_MSG_MISSING_TAGGER_ENTRY, "invalid format - expected 'tagger' line");
+		ret = report(options, oid, OBJ_TAG, FSCK_MSG_MISSING_TAGGER_ENTRY, "invalid format - expected 'tagger' line");
 		if (ret)
 			goto done;
 	}
 	else
-		ret = fsck_ident(&buffer, &tag->object, options);
+		ret = fsck_ident(&buffer, oid, OBJ_TAG, options);
 
 done:
 	strbuf_release(&sb);
-	free(to_free);
 	return ret;
 }
 
-static int fsck_tag(struct tag *tag, const char *data,
-	unsigned long size, struct fsck_options *options)
-{
-	struct object *tagged = tag->tagged;
-
-	if (!tagged)
-		return report(options, &tag->object, FSCK_MSG_BAD_TAG_OBJECT, "could not load tagged object");
-
-	return fsck_tag_buffer(tag, data, size, options);
-}
-
 struct fsck_gitmodules_data {
-	struct object *obj;
+	const struct object_id *oid;
 	struct fsck_options *options;
 	int ret;
 };
@@ -949,19 +912,22 @@ static int fsck_gitmodules_fn(const char *var, const char *value, void *vdata)
 
 	name = xmemdupz(subsection, subsection_len);
 	if (check_submodule_name(name) < 0)
-		data->ret |= report(data->options, data->obj,
+		data->ret |= report(data->options,
+				    data->oid, OBJ_BLOB,
 				    FSCK_MSG_GITMODULES_NAME,
 				    "disallowed submodule name: %s",
 				    name);
 	if (!strcmp(key, "url") && value &&
 	    looks_like_command_line_option(value))
-		data->ret |= report(data->options, data->obj,
+		data->ret |= report(data->options,
+				    data->oid, OBJ_BLOB,
 				    FSCK_MSG_GITMODULES_URL,
 				    "disallowed submodule url: %s",
 				    value);
 	if (!strcmp(key, "path") && value &&
 	    looks_like_command_line_option(value))
-		data->ret |= report(data->options, data->obj,
+		data->ret |= report(data->options,
+				    data->oid, OBJ_BLOB,
 				    FSCK_MSG_GITMODULES_PATH,
 				    "disallowed submodule path: %s",
 				    value);
@@ -970,17 +936,17 @@ static int fsck_gitmodules_fn(const char *var, const char *value, void *vdata)
 	return 0;
 }
 
-static int fsck_blob(struct blob *blob, const char *buf,
+static int fsck_blob(const struct object_id *oid, const char *buf,
 		     unsigned long size, struct fsck_options *options)
 {
 	struct fsck_gitmodules_data data;
 	struct config_options config_opts = { 0 };
 
-	if (!oidset_contains(&gitmodules_found, &blob->object.oid))
+	if (!oidset_contains(&gitmodules_found, oid))
 		return 0;
-	oidset_insert(&gitmodules_done, &blob->object.oid);
+	oidset_insert(&gitmodules_done, oid);
 
-	if (object_on_skiplist(options, &blob->object))
+	if (object_on_skiplist(options, oid))
 		return 0;
 
 	if (!buf) {
@@ -989,18 +955,18 @@ static int fsck_blob(struct blob *blob, const char *buf,
 		 * blob too gigantic to load into memory. Let's just consider
 		 * that an error.
 		 */
-		return report(options, &blob->object,
+		return report(options, oid, OBJ_BLOB,
 			      FSCK_MSG_GITMODULES_LARGE,
 			      ".gitmodules too large to parse");
 	}
 
-	data.obj = &blob->object;
+	data.oid = oid;
 	data.options = options;
 	data.ret = 0;
 	config_opts.error_action = CONFIG_ERROR_SILENT;
 	if (git_config_from_mem(fsck_gitmodules_fn, CONFIG_ORIGIN_BLOB,
 				".gitmodules", buf, size, &data, &config_opts))
-		data.ret |= report(options, &blob->object,
+		data.ret |= report(options, oid, OBJ_BLOB,
 				   FSCK_MSG_GITMODULES_PARSE,
 				   "could not parse gitmodules blob");
 
@@ -1011,31 +977,33 @@ int fsck_object(struct object *obj, void *data, unsigned long size,
 	struct fsck_options *options)
 {
 	if (!obj)
-		return report(options, obj, FSCK_MSG_BAD_OBJECT_SHA1, "no valid object to fsck");
+		return report(options, NULL, OBJ_NONE, FSCK_MSG_BAD_OBJECT_SHA1, "no valid object to fsck");
 
 	if (obj->type == OBJ_BLOB)
-		return fsck_blob((struct blob *)obj, data, size, options);
+		return fsck_blob(&obj->oid, data, size, options);
 	if (obj->type == OBJ_TREE)
-		return fsck_tree((struct tree *) obj, options);
+		return fsck_tree(&obj->oid, data, size, options);
 	if (obj->type == OBJ_COMMIT)
-		return fsck_commit((struct commit *) obj, (const char *) data,
-			size, options);
+		return fsck_commit(&obj->oid, data, size, options);
 	if (obj->type == OBJ_TAG)
-		return fsck_tag((struct tag *) obj, (const char *) data,
-			size, options);
+		return fsck_tag(&obj->oid, data, size, options);
 
-	return report(options, obj, FSCK_MSG_UNKNOWN_TYPE, "unknown type '%d' (internal fsck error)",
-			  obj->type);
+	return report(options, &obj->oid, obj->type,
+		      FSCK_MSG_UNKNOWN_TYPE,
+		      "unknown type '%d' (internal fsck error)",
+		      obj->type);
 }
 
 int fsck_error_function(struct fsck_options *o,
-	struct object *obj, int msg_type, const char *message)
+			const struct object_id *oid,
+			enum object_type object_type,
+			int msg_type, const char *message)
 {
 	if (msg_type == FSCK_WARN) {
-		warning("object %s: %s", describe_object(o, obj), message);
+		warning("object %s: %s", fsck_describe_object(o, oid), message);
 		return 0;
 	}
-	error("object %s: %s", describe_object(o, obj), message);
+	error("object %s: %s", fsck_describe_object(o, oid), message);
 	return 1;
 }
 
@@ -1047,7 +1015,6 @@ int fsck_finish(struct fsck_options *options)
 
 	oidset_iter_init(&gitmodules_found, &iter);
 	while ((oid = oidset_iter_next(&iter))) {
-		struct blob *blob;
 		enum object_type type;
 		unsigned long size;
 		char *buf;
@@ -1055,29 +1022,22 @@ int fsck_finish(struct fsck_options *options)
 		if (oidset_contains(&gitmodules_done, oid))
 			continue;
 
-		blob = lookup_blob(the_repository, oid);
-		if (!blob) {
-			struct object *obj = lookup_unknown_object(oid);
-			ret |= report(options, obj,
-				      FSCK_MSG_GITMODULES_BLOB,
-				      "non-blob found at .gitmodules");
-			continue;
-		}
-
 		buf = read_object_file(oid, &type, &size);
 		if (!buf) {
-			if (is_promisor_object(&blob->object.oid))
+			if (is_promisor_object(oid))
 				continue;
-			ret |= report(options, &blob->object,
+			ret |= report(options,
+				      oid, OBJ_BLOB,
 				      FSCK_MSG_GITMODULES_MISSING,
 				      "unable to read .gitmodules blob");
 			continue;
 		}
 
 		if (type == OBJ_BLOB)
-			ret |= fsck_blob(blob, buf, size, options);
+			ret |= fsck_blob(oid, buf, size, options);
 		else
-			ret |= report(options, &blob->object,
+			ret |= report(options,
+				      oid, type,
 				      FSCK_MSG_GITMODULES_BLOB,
 				      "non-blob found at .gitmodules");
 		free(buf);
diff --git a/fsck.h b/fsck.h
index b95595ae5f..69cf715e79 100644
--- a/fsck.h
+++ b/fsck.h
@@ -27,10 +27,12 @@ typedef int (*fsck_walk_func)(struct object *obj, int type, void *data, struct f
 
 /* callback for fsck_object, type is FSCK_ERROR or FSCK_WARN */
 typedef int (*fsck_error)(struct fsck_options *o,
-	struct object *obj, int type, const char *message);
+			  const struct object_id *oid, enum object_type object_type,
+			  int msg_type, const char *message);
 
 int fsck_error_function(struct fsck_options *o,
-	struct object *obj, int type, const char *message);
+			const struct object_id *oid, enum object_type object_type,
+			int msg_type, const char *message);
 
 struct fsck_options {
 	fsck_walk_func walk;
@@ -38,7 +40,7 @@ struct fsck_options {
 	unsigned strict:1;
 	int *msg_type;
 	struct oidset skiplist;
-	struct decoration *object_names;
+	kh_oid_map_t *object_names;
 };
 
 #define FSCK_OPTIONS_DEFAULT { NULL, fsck_error_function, 0, NULL, OIDSET_INIT }
@@ -52,7 +54,11 @@ struct fsck_options {
  *    0		everything OK
  */
 int fsck_walk(struct object *obj, void *data, struct fsck_options *options);
-/* If NULL is passed for data, we assume the object is local and read it. */
+
+/*
+ * Blob objects my pass a NULL data pointer, which indicates they are too large
+ * to fit in memory. All other types must pass a real buffer.
+ */
 int fsck_object(struct object *obj, void *data, unsigned long size,
 	struct fsck_options *options);
 
@@ -63,4 +69,29 @@ int fsck_object(struct object *obj, void *data, unsigned long size,
  */
 int fsck_finish(struct fsck_options *options);
 
+/*
+ * Subsystem for storing human-readable names for each object.
+ *
+ * If fsck_enable_object_names() has not been called, all other functions are
+ * noops.
+ *
+ * Use fsck_put_object_name() to seed initial names (e.g. from refnames); the
+ * fsck code will extend that while walking trees, etc.
+ *
+ * Use fsck_get_object_name() to get a single name (or NULL if none). Or the
+ * more convenient describe_object(), which always produces an output string
+ * with the oid combined with the name (if any). Note that the return value
+ * points to a rotating array of static buffers, and may be invalidated by a
+ * subsequent call.
+ */
+void fsck_enable_object_names(struct fsck_options *options);
+const char *fsck_get_object_name(struct fsck_options *options,
+				 const struct object_id *oid);
+__attribute__((format (printf,3,4)))
+void fsck_put_object_name(struct fsck_options *options,
+			  const struct object_id *oid,
+			  const char *fmt, ...);
+const char *fsck_describe_object(struct fsck_options *options,
+				 const struct object_id *oid);
+
 #endif
diff --git a/t/t1450-fsck.sh b/t/t1450-fsck.sh
index 50d28e6fdb..7c7ff7e961 100755
--- a/t/t1450-fsck.sh
+++ b/t/t1450-fsck.sh
@@ -616,7 +616,7 @@ test_expect_success 'fsck --name-objects' '
 		remove_object $(git rev-parse julius:caesar.t) &&
 		test_must_fail git fsck --name-objects >out &&
 		tree=$(git rev-parse --verify julius:) &&
-		test_i18ngrep -E "$tree \((refs/heads/master|HEAD)@\{[0-9]*\}:" out
+		test_i18ngrep "$tree (refs/tags/julius:" out
 	)
 '
 
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index d42b3efe39..127b404856 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -660,7 +660,7 @@ test_expect_success 'corrupt commit-graph write (missing tree)' '
 		git commit-tree -p "$broken" -m "good" "$tree" >good &&
 		test_must_fail git commit-graph write --stdin-commits \
 			<good 2>test_err &&
-		test_i18ngrep "unable to get tree for" test_err
+		test_i18ngrep "unable to parse commit" test_err
 	)
 '
 
diff --git a/t/t6102-rev-list-unexpected-objects.sh b/t/t6102-rev-list-unexpected-objects.sh
index 28611c978e..52cde097dd 100755
--- a/t/t6102-rev-list-unexpected-objects.sh
+++ b/t/t6102-rev-list-unexpected-objects.sh
@@ -52,7 +52,7 @@ test_expect_success 'traverse unexpected non-commit parent (lone)' '
 '
 
 test_expect_success 'traverse unexpected non-commit parent (seen)' '
-	test_must_fail git rev-list --objects $commit $broken_commit \
+	test_must_fail git rev-list --objects $blob $broken_commit \
 		>output 2>&1 &&
 	test_i18ngrep "not a commit" output
 '
diff --git a/tag.c b/tag.c
index bfa0e31435..71b544467e 100644
--- a/tag.c
+++ b/tag.c
@@ -141,7 +141,16 @@ int parse_tag_buffer(struct repository *r, struct tag *item, const void *data, u
 
 	if (item->object.parsed)
 		return 0;
-	item->object.parsed = 1;
+
+	if (item->tag) {
+		/*
+		 * Presumably left over from a previous failed parse;
+		 * clear it out in preparation for re-parsing (we'll probably
+		 * hit the same error, which lets us tell our current caller
+		 * about the problem).
+		 */
+		FREE_AND_NULL(item->tag);
+	}
 
 	if (size < the_hash_algo->hexsz + 24)
 		return -1;
@@ -167,10 +176,15 @@ int parse_tag_buffer(struct repository *r, struct tag *item, const void *data, u
 	} else if (!strcmp(type, tag_type)) {
 		item->tagged = (struct object *)lookup_tag(r, &oid);
 	} else {
-		error("Unknown type %s", type);
-		item->tagged = NULL;
+		return error("unknown tag type '%s' in %s",
+			     type, oid_to_hex(&item->object.oid));
 	}
 
+	if (!item->tagged)
+		return error("bad tag pointer to %s in %s",
+			     oid_to_hex(&oid),
+			     oid_to_hex(&item->object.oid));
+
 	if (bufptr + 4 < tail && starts_with(bufptr, "tag "))
 		; 		/* good */
 	else
@@ -187,6 +201,7 @@ int parse_tag_buffer(struct repository *r, struct tag *item, const void *data, u
 	else
 		item->date = 0;
 
+	item->object.parsed = 1;
 	return 0;
 }