Merge pull request #1624 from libgit2/vmg/full-ref-iterator

Breaking RefDB changes

16 files changed, 700 insertions, 542 deletions

diff --git a/src/branch.c b/src/branch.c
index dd6dc68f4..de38e3355 100644
--- a/src/branch.c
+++ b/src/branch.c
@@ -131,28 +131,32 @@ int git_branch_foreach(
 	void *payload)
 {
 	git_reference_iterator *iter;
-	const char *name;
+	git_reference *ref;
 	int error;
 
 	if (git_reference_iterator_new(&iter, repo) < 0)
 		return -1;
 
-	while ((error = git_reference_next(&name, iter)) == 0) {
+	while ((error = git_reference_next(&ref, iter)) == 0) {
 		if (list_flags & GIT_BRANCH_LOCAL &&
-		    git__prefixcmp(name, GIT_REFS_HEADS_DIR) == 0) {
-			if (callback(name + strlen(GIT_REFS_HEADS_DIR), GIT_BRANCH_LOCAL, payload)) {
+		    git__prefixcmp(ref->name, GIT_REFS_HEADS_DIR) == 0) {
+			if (callback(ref->name + strlen(GIT_REFS_HEADS_DIR),
+					GIT_BRANCH_LOCAL, payload)) {
 				error = GIT_EUSER;
 				break;
 			}
 		}
 
 		if (list_flags & GIT_BRANCH_REMOTE &&
-		    git__prefixcmp(name, GIT_REFS_REMOTES_DIR) == 0) {
-			if (callback(name + strlen(GIT_REFS_REMOTES_DIR), GIT_BRANCH_REMOTE, payload)) {
+		    git__prefixcmp(ref->name, GIT_REFS_REMOTES_DIR) == 0) {
+			if (callback(ref->name + strlen(GIT_REFS_REMOTES_DIR),
+					GIT_BRANCH_REMOTE, payload)) {
 				error = GIT_EUSER;
 				break;
 			}
 		}
+
+		git_reference_free(ref);
 	}
 
 	if (error == GIT_ITEROVER)
@@ -160,7 +164,6 @@ int git_branch_foreach(
 
 	git_reference_iterator_free(iter);
 	return error;
-
 }
 
 int git_branch_move(
@@ -179,18 +182,21 @@ int git_branch_move(
 	if (!git_reference_is_branch(branch))
 		return not_a_local_branch(git_reference_name(branch));
 
-	if ((error = git_buf_joinpath(&new_reference_name, GIT_REFS_HEADS_DIR, new_branch_name)) < 0 ||
-		(error = git_buf_printf(&old_config_section, "branch.%s", git_reference_name(branch) + strlen(GIT_REFS_HEADS_DIR))) < 0 ||
-		(error = git_buf_printf(&new_config_section, "branch.%s", new_branch_name)) < 0)
+	error = git_buf_joinpath(&new_reference_name, GIT_REFS_HEADS_DIR, new_branch_name);
+	if (error < 0)
 		goto done;
 
+	git_buf_printf(&old_config_section,
+		"branch.%s", git_reference_name(branch) + strlen(GIT_REFS_HEADS_DIR));
+
+	git_buf_printf(&new_config_section, "branch.%s", new_branch_name);
+
 	if ((error = git_config_rename_section(git_reference_owner(branch),
 		git_buf_cstr(&old_config_section),
 		git_buf_cstr(&new_config_section))) < 0)
 		goto done;
 
-	if ((error = git_reference_rename(out, branch, git_buf_cstr(&new_reference_name), force)) < 0)
-		goto done;
+	error = git_reference_rename(out, branch, git_buf_cstr(&new_reference_name), force);
 
 done:
 	git_buf_free(&new_reference_name);
diff --git a/src/checkout.c b/src/checkout.c
index c28fcdee0..7a2e68300 100644
--- a/src/checkout.c
+++ b/src/checkout.c
@@ -495,12 +495,9 @@ static int checkout_action(
 			if (cmp == 0) {
 				if (wd->mode == GIT_FILEMODE_TREE) {
 					/* case 2 - entry prefixed by workdir tree */
-					if ((error = git_iterator_advance_into(&wd, workdir)) < 0) {
-						if (error != GIT_ENOTFOUND ||
-							git_iterator_advance(&wd, workdir) < 0)
-							goto fail;
-					}
-
+					error = git_iterator_advance_into_or_over(&wd, workdir);
+					if (error && error != GIT_ITEROVER)
+						goto fail;
 					*wditem_ptr = wd;
 					continue;
 				}
@@ -515,8 +512,10 @@ static int checkout_action(
 			}
 
 			/* case 1 - handle wd item (if it matches pathspec) */
-			if (checkout_action_wd_only(data, workdir, wd, pathspec) < 0 ||
-				git_iterator_advance(&wd, workdir) < 0)
+			if (checkout_action_wd_only(data, workdir, wd, pathspec) < 0)
+				goto fail;
+			if ((error = git_iterator_advance(&wd, workdir)) < 0 &&
+				error != GIT_ITEROVER)
 				goto fail;
 
 			*wditem_ptr = wd;
@@ -539,8 +538,9 @@ static int checkout_action(
 			if (delta->status == GIT_DELTA_TYPECHANGE) {
 				if (delta->old_file.mode == GIT_FILEMODE_TREE) {
 					act = checkout_action_with_wd(data, delta, wd);
-					if (git_iterator_advance_into(&wd, workdir) < 0)
-						wd = NULL;
+					if ((error = git_iterator_advance_into(&wd, workdir)) < 0 &&
+						error != GIT_ENOTFOUND)
+						goto fail;
 					*wditem_ptr = wd;
 					return act;
 				}
@@ -550,8 +550,9 @@ static int checkout_action(
 					delta->old_file.mode == GIT_FILEMODE_COMMIT)
 				{
 					act = checkout_action_with_wd(data, delta, wd);
-					if (git_iterator_advance(&wd, workdir) < 0)
-						wd = NULL;
+					if ((error = git_iterator_advance(&wd, workdir)) < 0 &&
+						error != GIT_ITEROVER)
+						goto fail;
 					*wditem_ptr = wd;
 					return act;
 				}
@@ -582,6 +583,9 @@ static int checkout_remaining_wd_items(
 			error = git_iterator_advance(&wd, workdir);
 	}
 
+	if (error == GIT_ITEROVER)
+		error = 0;
+
 	return error;
 }
 
@@ -603,7 +607,8 @@ static int checkout_get_actions(
 		git_pathspec_init(&pathspec, &data->opts.paths, &pathpool) < 0)
 		return -1;
 
-	if ((error = git_iterator_current(&wditem, workdir)) < 0)
+	if ((error = git_iterator_current(&wditem, workdir)) < 0 &&
+		error != GIT_ITEROVER)
 		goto fail;
 
 	deltas = &data->diff->deltas;
diff --git a/src/clone.c b/src/clone.c
index 191040da7..af3298fd0 100644
--- a/src/clone.c
+++ b/src/clone.c
@@ -241,7 +241,7 @@ static int update_head_to_remote(git_repository *repo, git_remote *remote)
 	}
 
 	/* Not master. Check all the other refs. */
-	if (git_reference_foreach(
+	if (git_reference_foreach_name(
 		repo,
 		reference_matches_remote_head,
 		&head_info) < 0)
diff --git a/src/diff.c b/src/diff.c
index b96ff4705..05ef4f16b 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -796,6 +796,9 @@ static int diff_scan_inside_untracked_dir(
 done:
 	git_buf_free(&base);
 
+	if (error == GIT_ITEROVER)
+		error = 0;
+
 	return error;
 }
 
@@ -981,8 +984,11 @@ static int handle_matched_item(
 {
 	int error = 0;
 
-	if (!(error = maybe_modified(diff, info)) &&
-		!(error = git_iterator_advance(&info->oitem, info->old_iter)))
+	if ((error = maybe_modified(diff, info)) < 0)
+		return error;
+
+	if (!(error = git_iterator_advance(&info->oitem, info->old_iter)) ||
+		error == GIT_ITEROVER)
 		error = git_iterator_advance(&info->nitem, info->new_iter);
 
 	return error;
@@ -1011,15 +1017,22 @@ int git_diff__from_iterators(
 
 	/* make iterators have matching icase behavior */
 	if (DIFF_FLAG_IS_SET(diff, GIT_DIFF_DELTAS_ARE_ICASE)) {
-		if (!(error = git_iterator_set_ignore_case(old_iter, true)))
-			error = git_iterator_set_ignore_case(new_iter, true);
+		if ((error = git_iterator_set_ignore_case(old_iter, true)) < 0 ||
+			(error = git_iterator_set_ignore_case(new_iter, true)) < 0)
+			goto cleanup;
 	}
 
 	/* finish initialization */
-	if (!error &&
-		!(error = diff_list_apply_options(diff, opts)) &&
-		!(error = git_iterator_current(&info.oitem, old_iter)))
-		error = git_iterator_current(&info.nitem, new_iter);
+	if ((error = diff_list_apply_options(diff, opts)) < 0)
+		goto cleanup;
+
+	if ((error = git_iterator_current(&info.oitem, old_iter)) < 0 &&
+		error != GIT_ITEROVER)
+		goto cleanup;
+	if ((error = git_iterator_current(&info.nitem, new_iter)) < 0 &&
+		error != GIT_ITEROVER)
+		goto cleanup;
+	error = 0;
 
 	/* run iterators building diffs */
 	while (!error && (info.oitem || info.nitem)) {
@@ -1041,8 +1054,13 @@ int git_diff__from_iterators(
 		 */
 		else
 			error = handle_matched_item(diff, &info);
+
+		/* because we are iterating over two lists, ignore ITEROVER */
+		if (error == GIT_ITEROVER)
+			error = 0;
 	}
 
+cleanup:
 	if (!error)
 		*diff_ptr = diff;
 	else
diff --git a/src/iterator.c b/src/iterator.c
index ff08c1ce0..4360b99ad 100644
--- a/src/iterator.c
+++ b/src/iterator.c
@@ -46,6 +46,9 @@
 #define iterator__dont_autoexpand(I) iterator__flag(I,DONT_AUTOEXPAND)
 #define iterator__do_autoexpand(I)   !iterator__flag(I,DONT_AUTOEXPAND)
 
+#define GIT_ITERATOR_FIRST_ACCESS (1 << 15)
+#define iterator__has_been_accessed(I) iterator__flag(I,FIRST_ACCESS)
+
 #define iterator__end(I) ((git_iterator *)(I))->end
 #define iterator__past_end(I,PATH) \
 	(iterator__end(I) && ((git_iterator *)(I))->prefixcomp((PATH),iterator__end(I)) > 0)
@@ -68,6 +71,8 @@ static int iterator__reset_range(
 		GITERR_CHECK_ALLOC(iter->end);
 	}
 
+	iter->flags &= ~GIT_ITERATOR_FIRST_ACCESS;
+
 	return 0;
 }
 
@@ -109,7 +114,7 @@ static int empty_iterator__noop(const git_index_entry **e, git_iterator *i)
 {
 	GIT_UNUSED(i);
 	iterator__clear_entry(e);
-	return 0;
+	return GIT_ITEROVER;
 }
 
 static int empty_iterator__seek(git_iterator *i, const char *p)
@@ -193,6 +198,7 @@ typedef struct {
 	git_buf path;
 	int path_ambiguities;
 	bool path_has_filename;
+	bool entry_is_current;
 	int (*strncomp)(const char *a, const char *b, size_t sz);
 } tree_iterator;
 
@@ -266,9 +272,28 @@ static int tree_iterator__search_cmp(const void *key, const void *val, void *p)
 		((tree_iterator *)p)->strncomp);
 }
 
+static bool tree_iterator__move_to_next(
+	tree_iterator *ti, tree_iterator_frame *tf)
+{
+	if (tf->next > tf->current + 1)
+		ti->path_ambiguities--;
+
+	if (!tf->up) { /* at root */
+		tf->current = tf->next;
+		return false;
+	}
+
+	for (; tf->current < tf->next; tf->current++) {
+		git_tree_free(tf->entries[tf->current]->tree);
+		tf->entries[tf->current]->tree = NULL;
+	}
+
+	return (tf->current < tf->n_entries);
+}
+
 static int tree_iterator__set_next(tree_iterator *ti, tree_iterator_frame *tf)
 {
-	int error;
+	int error = 0;
 	const git_tree_entry *te, *last = NULL;
 
 	tf->next = tf->current;
@@ -279,18 +304,23 @@ static int tree_iterator__set_next(tree_iterator *ti, tree_iterator_frame *tf)
 		if (last && tree_iterator__te_cmp(last, te, ti->strncomp))
 			break;
 
-		/* load trees for items in [current,next) range */
-		if (git_tree_entry__is_tree(te) &&
-			(error = git_tree_lookup(
-				&tf->entries[tf->next]->tree, ti->base.repo, &te->oid)) < 0)
-			return error;
+		/* try to load trees for items in [current,next) range */
+		if (!error && git_tree_entry__is_tree(te))
+			error = git_tree_lookup(
+				&tf->entries[tf->next]->tree, ti->base.repo, &te->oid);
 	}
 
 	if (tf->next > tf->current + 1)
 		ti->path_ambiguities++;
 
+	/* if a tree lookup failed, advance over this span and return failure */
+	if (error < 0) {
+		tree_iterator__move_to_next(ti, tf);
+		return error;
+	}
+
 	if (last && !tree_iterator__current_filename(ti, last))
-		return -1;
+		return -1; /* must have been allocation failure */
 
 	return 0;
 }
@@ -308,7 +338,7 @@ static int tree_iterator__push_frame(tree_iterator *ti)
 	size_t i, n_entries = 0;
 
 	if (head->current >= head->n_entries || !head->entries[head->current]->tree)
-		return 0;
+		return GIT_ITEROVER;
 
 	for (i = head->current; i < head->next; ++i)
 		n_entries += git_tree_entrycount(head->entries[i]->tree);
@@ -359,7 +389,7 @@ static int tree_iterator__push_frame(tree_iterator *ti)
 		}
 	}
 
-	ti->path_has_filename = false;
+	ti->path_has_filename = ti->entry_is_current = false;
 
 	if ((error = tree_iterator__set_next(ti, tf)) < 0)
 		return error;
@@ -371,25 +401,6 @@ static int tree_iterator__push_frame(tree_iterator *ti)
 	return 0;
 }
 
-static bool tree_iterator__move_to_next(
-	tree_iterator *ti, tree_iterator_frame *tf)
-{
-	if (tf->next > tf->current + 1)
-		ti->path_ambiguities--;
-
-	if (!tf->up) { /* at root */
-		tf->current = tf->next;
-		return false;
-	}
-
-	for (; tf->current < tf->next; tf->current++) {
-		git_tree_free(tf->entries[tf->current]->tree);
-		tf->entries[tf->current]->tree = NULL;
-	}
-
-	return (tf->current < tf->n_entries);
-}
-
 static bool tree_iterator__pop_frame(tree_iterator *ti, bool final)
 {
 	tree_iterator_frame *tf = ti->head;
@@ -412,7 +423,7 @@ static bool tree_iterator__pop_frame(tree_iterator *ti, bool final)
 	return true;
 }
 
-static int tree_iterator__pop_all(tree_iterator *ti, bool to_end, bool final)
+static void tree_iterator__pop_all(tree_iterator *ti, bool to_end, bool final)
 {
 	while (tree_iterator__pop_frame(ti, final)) /* pop to root */;
 
@@ -421,22 +432,18 @@ static int tree_iterator__pop_all(tree_iterator *ti, bool to_end, bool final)
 		ti->path_ambiguities = 0;
 		git_buf_clear(&ti->path);
 	}
-
-	return 0;
 }
 
-static int tree_iterator__current(
-	const git_index_entry **entry, git_iterator *self)
+static int tree_iterator__update_entry(tree_iterator *ti)
 {
-	tree_iterator *ti = (tree_iterator *)self;
-	tree_iterator_frame *tf = ti->head;
-	const git_tree_entry *te;
+	tree_iterator_frame *tf;
+    const git_tree_entry *te;
 
-	iterator__clear_entry(entry);
+	if (ti->entry_is_current)
+        return 0;
 
-	if (tf->current >= tf->n_entries)
-		return 0;
-	te = tf->entries[tf->current]->te;
+	tf = ti->head;
+    te = tf->entries[tf->current]->te;
 
 	ti->entry.mode = te->attr;
 	git_oid_cpy(&ti->entry.oid, &te->oid);
@@ -447,12 +454,36 @@ static int tree_iterator__current(
 	if (ti->path_ambiguities > 0)
 		tree_iterator__rewrite_filename(ti);
 
-	if (iterator__past_end(ti, ti->entry.path))
-		return tree_iterator__pop_all(ti, true, false);
+	if (iterator__past_end(ti, ti->entry.path)) {
+		tree_iterator__pop_all(ti, true, false);
+		return GIT_ITEROVER;
+	}
+
+	ti->entry_is_current = true;
+
+	return 0;
+}
+
+static int tree_iterator__current(
+	const git_index_entry **entry, git_iterator *self)
+{
+	int error;
+	tree_iterator *ti = (tree_iterator *)self;
+	tree_iterator_frame *tf = ti->head;
+
+	iterator__clear_entry(entry);
+
+	if (tf->current >= tf->n_entries)
+		return GIT_ITEROVER;
+
+	if ((error = tree_iterator__update_entry(ti)) < 0)
+		return error;
 
 	if (entry)
 		*entry = &ti->entry;
 
+	ti->base.flags |= GIT_ITERATOR_FIRST_ACCESS;
+
 	return 0;
 }
 
@@ -464,8 +495,10 @@ static int tree_iterator__advance_into(
 
 	iterator__clear_entry(entry);
 
-	if (tree_iterator__at_tree(ti) &&
-		!(error = tree_iterator__push_frame(ti)))
+	if (tree_iterator__at_tree(ti))
+		error = tree_iterator__push_frame(ti);
+
+	if (!error && entry)
 		error = tree_iterator__current(entry, self);
 
 	return error;
@@ -480,8 +513,11 @@ static int tree_iterator__advance(
 
 	iterator__clear_entry(entry);
 
-	if (tf->current > tf->n_entries)
-		return 0;
+	if (tf->current >= tf->n_entries)
+		return GIT_ITEROVER;
+
+	if (!iterator__has_been_accessed(ti))
+		return tree_iterator__current(entry, self);
 
 	if (iterator__do_autoexpand(ti) && iterator__include_trees(ti) &&
 		tree_iterator__at_tree(ti))
@@ -489,7 +525,7 @@ static int tree_iterator__advance(
 
 	if (ti->path_has_filename) {
 		git_buf_rtruncate_at_char(&ti->path, '/');
-		ti->path_has_filename = false;
+		ti->path_has_filename = ti->entry_is_current = false;
 	}
 
 	/* scan forward and up, advancing in frame or popping frame when done */
@@ -699,7 +735,9 @@ static int index_iterator__current(
 	if (entry)
 		*entry = ie;
 
-	return 0;
+	ii->base.flags |= GIT_ITERATOR_FIRST_ACCESS;
+
+	return (ie != NULL) ? 0 : GIT_ITEROVER;
 }
 
 static int index_iterator__at_end(git_iterator *self)
@@ -715,6 +753,9 @@ static int index_iterator__advance(
 	size_t entrycount = git_index_entrycount(ii->index);
 	const git_index_entry *ie;
 
+	if (!iterator__has_been_accessed(ii))
+		return index_iterator__current(entry, self);
+
 	if (index_iterator__at_tree(ii)) {
 		if (iterator__do_autoexpand(ii)) {
 			ii->partial.ptr[ii->partial_pos] = ii->restore_terminator;
@@ -906,6 +947,8 @@ static void fs_iterator__pop_frame(
 }
 
 static int fs_iterator__update_entry(fs_iterator *fi);
+static int fs_iterator__advance_over(
+	const git_index_entry **entry, git_iterator *self);
 
 static int fs_iterator__entry_cmp(const void *i, const void *item)
 {
@@ -945,7 +988,13 @@ static int fs_iterator__expand_dir(fs_iterator *fi)
 		fi->path.ptr, fi->root_len, iterator__ignore_case(fi),
 		fi->base.start, fi->base.end, &ff->entries);
 
-	if (error < 0 || ff->entries.length == 0) {
+	if (error < 0) {
+		fs_iterator__free_frame(ff);
+		fs_iterator__advance_over(NULL, (git_iterator *)fi);
+		return error;
+	}
+
+	if (ff->entries.length == 0) {
 		fs_iterator__free_frame(ff);
 		return GIT_ENOTFOUND;
 	}
@@ -966,9 +1015,14 @@ static int fs_iterator__current(
 	const git_index_entry **entry, git_iterator *self)
 {
 	fs_iterator *fi = (fs_iterator *)self;
+	const git_index_entry *fe = (fi->entry.path == NULL) ? NULL : &fi->entry;
+
 	if (entry)
-		*entry = (fi->entry.path == NULL) ? NULL : &fi->entry;
-	return 0;
+		*entry = fe;
+
+	fi->base.flags |= GIT_ITERATOR_FIRST_ACCESS;
+
+	return (fe != NULL) ? 0 : GIT_ITEROVER;
 }
 
 static int fs_iterator__at_end(git_iterator *self)
@@ -998,6 +1052,9 @@ static int fs_iterator__advance_into(
 	if (!error && entry)
 		error = fs_iterator__current(entry, iter);
 
+	if (!error && !fi->entry.path)
+		error = GIT_ITEROVER;
+
 	return error;
 }
 
@@ -1035,6 +1092,9 @@ static int fs_iterator__advance(
 {
 	fs_iterator *fi = (fs_iterator *)self;
 
+	if (!iterator__has_been_accessed(fi))
+		return fs_iterator__current(entry, self);
+
 	/* given include_trees & autoexpand, we might have to go into a tree */
 	if (iterator__do_autoexpand(fi) &&
 		fi->entry.path != NULL &&
@@ -1063,18 +1123,23 @@ static int fs_iterator__seek(git_iterator *self, const char *prefix)
 static int fs_iterator__reset(
 	git_iterator *self, const char *start, const char *end)
 {
+	int error;
 	fs_iterator *fi = (fs_iterator *)self;
 
 	while (fi->stack != NULL && fi->stack->next != NULL)
 		fs_iterator__pop_frame(fi, fi->stack, false);
 	fi->depth = 0;
 
-	if (iterator__reset_range(self, start, end) < 0)
-		return -1;
+	if ((error = iterator__reset_range(self, start, end)) < 0)
+		return error;
 
 	fs_iterator__seek_frame_start(fi, fi->stack);
 
-	return fs_iterator__update_entry(fi);
+	error = fs_iterator__update_entry(fi);
+	if (error == GIT_ITEROVER)
+		error = 0;
+
+	return error;
 }
 
 static void fs_iterator__free(git_iterator *self)
@@ -1089,18 +1154,23 @@ static void fs_iterator__free(git_iterator *self)
 
 static int fs_iterator__update_entry(fs_iterator *fi)
 {
-	git_path_with_stat *ps =
-		git_vector_get(&fi->stack->entries, fi->stack->index);
+	git_path_with_stat *ps;
 
-	git_buf_truncate(&fi->path, fi->root_len);
 	memset(&fi->entry, 0, sizeof(fi->entry));
 
+	if (!fi->stack)
+		return GIT_ITEROVER;
+
+	ps = git_vector_get(&fi->stack->entries, fi->stack->index);
 	if (!ps)
-		return 0;
+		return GIT_ITEROVER;
+
+	git_buf_truncate(&fi->path, fi->root_len);
 	if (git_buf_put(&fi->path, ps->path, ps->path_len) < 0)
 		return -1;
+
 	if (iterator__past_end(fi, fi->path.ptr + fi->root_len))
-		return 0;
+		return GIT_ITEROVER;
 
 	fi->entry.path = ps->path;
 	git_index_entry__init_from_stat(&fi->entry, &ps->st);
@@ -1114,8 +1184,13 @@ static int fs_iterator__update_entry(fs_iterator *fi)
 		return fs_iterator__advance_over(NULL, (git_iterator *)fi);
 
 	/* if this is a tree and trees aren't included, then skip */
-	if (fi->entry.mode == GIT_FILEMODE_TREE && !iterator__include_trees(fi))
-		return git_iterator_advance(NULL, (git_iterator *)fi);
+	if (fi->entry.mode == GIT_FILEMODE_TREE && !iterator__include_trees(fi)) {
+		int error = fs_iterator__advance_into(NULL, (git_iterator *)fi);
+		if (error != GIT_ENOTFOUND)
+			return error;
+		giterr_clear();
+		return fs_iterator__advance_over(NULL, (git_iterator *)fi);
+	}
 
 	return 0;
 }
@@ -1131,13 +1206,14 @@ static int fs_iterator__initialize(
 	}
 	fi->root_len = fi->path.size;
 
-	if ((error = fs_iterator__expand_dir(fi)) == GIT_ENOTFOUND) {
-		giterr_clear();
-		error = 0;
-	}
-	if (error) {
-		git_iterator_free((git_iterator *)fi);
-		fi = NULL;
+	if ((error = fs_iterator__expand_dir(fi)) < 0) {
+		if (error == GIT_ENOTFOUND || error == GIT_ITEROVER) {
+			giterr_clear();
+			error = 0;
+		} else {
+			git_iterator_free((git_iterator *)fi);
+			fi = NULL;
+		}
 	}
 
 	*out = (git_iterator *)fi;
diff --git a/src/iterator.h b/src/iterator.h
index 7998f7c6b..493ff4b2a 100644
--- a/src/iterator.h
+++ b/src/iterator.h
@@ -142,9 +142,9 @@ GIT_INLINE(int) git_iterator_advance(
  *
  * If the current item is not a tree, this is a no-op.
  *
- * For working directory iterators only, a tree (i.e. directory) can be
- * empty.  In that case, this function returns GIT_ENOTFOUND and does not
- * advance.  That can't happen for tree and index iterators.
+ * For filesystem and working directory iterators, a tree (i.e. directory)
+ * can be empty.  In that case, this function returns GIT_ENOTFOUND and
+ * does not advance.  That can't happen for tree and index iterators.
  */
 GIT_INLINE(int) git_iterator_advance_into(
 	const git_index_entry **entry, git_iterator *iter)
@@ -152,18 +152,50 @@ GIT_INLINE(int) git_iterator_advance_into(
 	return iter->cb->advance_into(entry, iter);
 }
 
+/**
+ * Advance into a tree or skip over it if it is empty.
+ *
+ * Because `git_iterator_advance_into` may return GIT_ENOTFOUND if the
+ * directory is empty (only with filesystem and working directory
+ * iterators) and a common response is to just call `git_iterator_advance`
+ * when that happens, this bundles the two into a single simple call.
+ */
+GIT_INLINE(int) git_iterator_advance_into_or_over(
+	const git_index_entry **entry, git_iterator *iter)
+{
+	int error = iter->cb->advance_into(entry, iter);
+	if (error == GIT_ENOTFOUND) {
+		giterr_clear();
+		error = iter->cb->advance(entry, iter);
+	}
+	return error;
+}
+
+/* Seek is currently unimplemented */
 GIT_INLINE(int) git_iterator_seek(
 	git_iterator *iter, const char *prefix)
 {
 	return iter->cb->seek(iter, prefix);
 }
 
+/**
+ * Go back to the start of the iteration.
+ *
+ * This resets the iterator to the start of the iteration.  It also allows
+ * you to reset the `start` and `end` pathname boundaries of the iteration
+ * when doing so.
+ */
 GIT_INLINE(int) git_iterator_reset(
 	git_iterator *iter, const char *start, const char *end)
 {
 	return iter->cb->reset(iter, start, end);
 }
 
+/**
+ * Check if the iterator is at the end
+ *
+ * @return 0 if not at end, >0 if at end
+ */
 GIT_INLINE(int) git_iterator_at_end(git_iterator *iter)
 {
 	return iter->cb->at_end(iter);
diff --git a/src/merge.c b/src/merge.c
index 11345587c..047d96013 100644
--- a/src/merge.c
+++ b/src/merge.c
@@ -1259,7 +1259,8 @@ int git_merge_diff_list__find_differences(
 
 	/* Set up the iterators */
 	for (i = 0; i < 3; i++) {
-		if ((error = git_iterator_current(&items[i], iterators[i])) < 0)
+		error = git_iterator_current(&items[i], iterators[i]);
+		if (error < 0 && error != GIT_ITEROVER)
 			goto done;
 	}
 
@@ -1313,11 +1314,16 @@ int git_merge_diff_list__find_differences(
 			error = merge_index_insert_conflict(diff_list, &df_data, cur_items);
 		else
 			error = merge_index_insert_unmodified(diff_list, cur_items);
+		if (error < 0)
+			goto done;
 
 		/* Advance each iterator that participated */
 		for (i = 0; i < 3; i++) {
-			if (cur_items[i] != NULL &&
-				(error = git_iterator_advance(&items[i], iterators[i])) < 0)
+			if (cur_items[i] == NULL)
+				continue;
+
+			error = git_iterator_advance(&items[i], iterators[i]);
+			if (error < 0 && error != GIT_ITEROVER)
 				goto done;
 		}
 	}
@@ -1326,6 +1332,9 @@ done:
 	for (i = 0; i < 3; i++)
 		git_iterator_free(iterators[i]);
 
+	if (error == GIT_ITEROVER)
+		error = 0;
+
 	return error;
 }
 
diff --git a/src/notes.c b/src/notes.c
index 3e3db58db..beace1b50 100644
--- a/src/notes.c
+++ b/src/notes.c
@@ -647,18 +647,12 @@ int git_note_next(
 	const git_index_entry *item;
 
 	if ((error = git_iterator_current(&item, it)) < 0)
-		goto exit;
+		return error;
 
-	if (item != NULL) {
-		git_oid_cpy(note_id, &item->oid);
-		error = process_entry_path(item->path, annotated_id);
+	git_oid_cpy(note_id, &item->oid);
 
-		if (error >= 0)
-			error = git_iterator_advance(NULL, it);
-	} else {
-		error = GIT_ITEROVER;
-	}
+	if (!(error = process_entry_path(item->path, annotated_id)))
+		git_iterator_advance(NULL, it);
 
-exit:
 	return error;
 }
diff --git a/src/refdb.c b/src/refdb.c
index 9f9037ce7..359842e44 100644
--- a/src/refdb.c
+++ b/src/refdb.c
@@ -86,7 +86,7 @@ int git_refdb_compress(git_refdb *db)
 	return 0;
 }
 
-static void refdb_free(git_refdb *db)
+void git_refdb__free(git_refdb *db)
 {
 	refdb_free_backend(db);
 	git__free(db);
@@ -97,7 +97,7 @@ void git_refdb_free(git_refdb *db)
 	if (db == NULL)
 		return;
 
-	GIT_REFCOUNT_DEC(db, refdb_free);
+	GIT_REFCOUNT_DEC(db, git_refdb__free);
 }
 
 int git_refdb_exists(int *exists, git_refdb *refdb, const char *ref_name)
@@ -114,90 +114,91 @@ int git_refdb_lookup(git_reference **out, git_refdb *db, const char *ref_name)
 
 	assert(db && db->backend && out && ref_name);
 
-	if (!(error = db->backend->lookup(&ref, db->backend, ref_name))) {
-		ref->db = db;
-		*out = ref;
-	} else {
-		*out = NULL;
-	}
+	error = db->backend->lookup(&ref, db->backend, ref_name);
+	if (error < 0)
+		return error;
+
+	GIT_REFCOUNT_INC(db);
+	ref->db = db;
 
-	return error;
+	*out = ref;
+	return 0;
 }
 
-int git_refdb_iterator(git_reference_iterator **out, git_refdb *db)
+int git_refdb_iterator(git_reference_iterator **out, git_refdb *db, const char *glob)
 {
 	if (!db->backend || !db->backend->iterator) {
 		giterr_set(GITERR_REFERENCE, "This backend doesn't support iterators");
 		return -1;
 	}
 
-	if (db->backend->iterator(out, db->backend) < 0)
+	if (db->backend->iterator(out, db->backend, glob) < 0)
 		return -1;
 
+	GIT_REFCOUNT_INC(db);
+	(*out)->db = db;
+
 	return 0;
 }
 
-int git_refdb_iterator_glob(git_reference_iterator **out, git_refdb *db, const char *glob)
+int git_refdb_iterator_next(git_reference **out, git_reference_iterator *iter)
 {
-	if (!db->backend) {
-		giterr_set(GITERR_REFERENCE, "There are no backends loaded");
-		return -1;
-	}
+	int error;
 
-	if (db->backend->iterator_glob)
-		return db->backend->iterator_glob(out, db->backend, glob);
+	if ((error = iter->next(out, iter)) < 0)
+		return error;
 
-	/* If the backend doesn't support glob-filtering themselves, we have to do it */
-	if (db->backend->iterator(out, db->backend) < 0)
-		return -1;
-
-	(*out)->glob = git__strdup(glob);
-	if (!(*out)->glob) {
-		db->backend->iterator_free(*out);
-		return -1;
-	}
+	GIT_REFCOUNT_INC(iter->db);
+	(*out)->db = iter->db;
 
 	return 0;
 }
 
-int git_refdb_next(const char **out, git_reference_iterator *iter)
+int git_refdb_iterator_next_name(const char **out, git_reference_iterator *iter)
 {
-	int error;
-
-	if (!iter->glob)
-		return iter->backend->next(out, iter);
-
-	/* If the iterator has a glob, we need to filter */
-	while ((error = iter->backend->next(out, iter)) == 0) {
-		if (!p_fnmatch(iter->glob, *out, 0))
-			break;
-	}
-
-	return error;
+	return iter->next_name(out, iter);
 }
 
 void git_refdb_iterator_free(git_reference_iterator *iter)
 {
-	git__free(iter->glob);
-	iter->backend->iterator_free(iter);
+	GIT_REFCOUNT_DEC(iter->db, git_refdb__free);
+	iter->free(iter);
 }
 
-struct glob_cb_data {
-	const char *glob;
-	git_reference_foreach_cb callback;
-	void *payload;
-};
-
-int git_refdb_write(git_refdb *db, const git_reference *ref)
+int git_refdb_write(git_refdb *db, git_reference *ref, int force)
 {
 	assert(db && db->backend);
 
-	return db->backend->write(db->backend, ref);
+	GIT_REFCOUNT_INC(db);
+	ref->db = db;
+
+	return db->backend->write(db->backend, ref, force);
 }
 
-int git_refdb_delete(struct git_refdb *db, const git_reference *ref)
+int git_refdb_rename(
+	git_reference **out,
+	git_refdb *db,
+	const char *old_name,
+	const char *new_name,
+	int force)
 {
+	int error;
+
 	assert(db && db->backend);
+	error = db->backend->rename(out, db->backend, old_name, new_name, force);
+	if (error < 0)
+		return error;
 
-	return db->backend->delete(db->backend, ref);
+	if (out) {
+		GIT_REFCOUNT_INC(db);
+		(*out)->db = db;
+	}
+
+	return 0;
+}
+
+int git_refdb_delete(struct git_refdb *db, const char *ref_name)
+{
+	assert(db && db->backend);
+	return db->backend->delete(db->backend, ref_name);
 }
diff --git a/src/refdb.h b/src/refdb.h
index 2edd05d18..3aea37b62 100644
--- a/src/refdb.h
+++ b/src/refdb.h
@@ -16,6 +16,8 @@ struct git_refdb {
 	git_refdb_backend *backend;
 };
 
+void git_refdb__free(git_refdb *db);
+
 int git_refdb_exists(
 	int *exists,
 	git_refdb *refdb,
@@ -26,13 +28,19 @@ int git_refdb_lookup(
 	git_refdb *refdb,
 	const char *ref_name);
 
-int git_refdb_iterator(git_reference_iterator **out, git_refdb *db);
-int git_refdb_iterator_glob(git_reference_iterator **out, git_refdb *db, const char *glob);
-int git_refdb_next(const char **out, git_reference_iterator *iter);
+int git_refdb_rename(
+	git_reference **out,
+	git_refdb *db,
+	const char *old_name,
+	const char *new_name,
+	int force);
+
+int git_refdb_iterator(git_reference_iterator **out, git_refdb *db, const char *glob);
+int git_refdb_iterator_next(git_reference **out, git_reference_iterator *iter);
+int git_refdb_iterator_next_name(const char **out, git_reference_iterator *iter);
 void git_refdb_iterator_free(git_reference_iterator *iter);
 
-int git_refdb_write(git_refdb *refdb, const git_reference *ref);
-
-int git_refdb_delete(git_refdb *refdb, const git_reference *ref);
+int git_refdb_write(git_refdb *refdb, git_reference *ref, int force);
+int git_refdb_delete(git_refdb *refdb, const char *ref_name);
 
 #endif
diff --git a/src/refdb_fs.c b/src/refdb_fs.c
index 7de56a1a0..4083ba9e5 100644
--- a/src/refdb_fs.c
+++ b/src/refdb_fs.c
@@ -29,7 +29,8 @@ GIT__USE_STRMAP;
 enum {
 	PACKREF_HAS_PEEL = 1,
 	PACKREF_WAS_LOOSE = 2,
-	PACKREF_CANNOT_PEEL = 4
+	PACKREF_CANNOT_PEEL = 4,
+	PACKREF_SHADOWED = 8,
 };
 
 enum {
@@ -115,11 +116,8 @@ static int packed_parse_oid(
 
 	git_oid_cpy(&ref->oid, &id);
 
-	ref->flags = 0;
-
 	*ref_out = ref;
 	*buffer_out = refname_end + 1;
-
 	return 0;
 
 corrupt:
@@ -552,139 +550,239 @@ static int refdb_fs_backend__lookup(
 	return result;
 }
 
-struct dirent_list_data {
-	refdb_fs_backend *backend;
-	size_t repo_path_len;
-	unsigned int list_type:2;
-
-	git_reference_foreach_cb callback;
-	void *callback_payload;
-	int callback_error;
-};
-
 typedef struct {
 	git_reference_iterator parent;
-	unsigned int loose;
-	/* packed */
-	git_strmap *h;
-	khiter_t k;
-	/* loose */
-	git_iterator *fsiter;
-	git_buf buf;
+
+	char *glob;
+	git_vector loose;
+	unsigned int loose_pos;
+	khiter_t packed_pos;
 } refdb_fs_iter;
 
-static int refdb_fs_backend__iterator(git_reference_iterator **out, git_refdb_backend *_backend)
+static void refdb_fs_backend__iterator_free(git_reference_iterator *_iter)
 {
-	refdb_fs_iter *iter;
-	refdb_fs_backend *backend;
+	refdb_fs_iter *iter = (refdb_fs_iter *) _iter;
+	char *loose_path;
+	size_t i;
 
-	assert(_backend);
-	backend = (refdb_fs_backend *)_backend;
+	git_vector_foreach(&iter->loose, i, loose_path) {
+		git__free(loose_path);
+	}
 
-	if (packed_load(backend) < 0)
+	git_vector_free(&iter->loose);
+
+	git__free(iter->glob);
+	git__free(iter);
+}
+
+static int iter_load_loose_paths(refdb_fs_backend *backend, refdb_fs_iter *iter)
+{
+	git_strmap *packfile = backend->refcache.packfile;
+	git_buf path = GIT_BUF_INIT;
+	git_iterator *fsit;
+	const git_index_entry *entry = NULL;
+
+	if (!backend->path) /* do nothing if no path for loose refs */
+		return 0;
+
+	if (git_buf_printf(&path, "%s/refs", backend->path) < 0)
 		return -1;
 
-	iter = git__calloc(1, sizeof(refdb_fs_iter));
-	GITERR_CHECK_ALLOC(iter);
+	if (git_iterator_for_filesystem(&fsit, git_buf_cstr(&path), 0, NULL, NULL) < 0)
+		return -1;
 
-	iter->parent.backend = _backend;
-	iter->h = backend->refcache.packfile;
-	iter->k = kh_begin(backend->refcache.packfile);
+	git_vector_init(&iter->loose, 8, NULL);
+	git_buf_sets(&path, GIT_REFS_DIR);
 
-	*out = (git_reference_iterator *)iter;
+	while (!git_iterator_advance(&entry, fsit)) {
+		const char *ref_name;
+		khiter_t pos;
+
+		git_buf_truncate(&path, strlen(GIT_REFS_DIR));
+		git_buf_puts(&path, entry->path);
+		ref_name = git_buf_cstr(&path);
+
+		if (git__suffixcmp(ref_name, ".lock") == 0 ||
+			(iter->glob && p_fnmatch(iter->glob, ref_name, 0) != 0))
+			continue;
+
+		pos = git_strmap_lookup_index(packfile, ref_name);
+		if (git_strmap_valid_index(packfile, pos)) {
+			struct packref *ref = git_strmap_value_at(packfile, pos);
+			ref->flags |= PACKREF_SHADOWED;
+		}
+
+		git_vector_insert(&iter->loose, git__strdup(ref_name));
+	}
+
+	git_iterator_free(fsit);
+	git_buf_free(&path);
 
 	return 0;
 }
 
-static void refdb_fs_backend__iterator_free(git_reference_iterator *_iter)
+static int refdb_fs_backend__iterator_next(
+	git_reference **out, git_reference_iterator *_iter)
 {
-	refdb_fs_iter *iter = (refdb_fs_iter *) _iter;
+	refdb_fs_iter *iter = (refdb_fs_iter *)_iter;
+	refdb_fs_backend *backend = (refdb_fs_backend *)iter->parent.db->backend;
+	git_strmap *packfile = backend->refcache.packfile;
 
-	git_buf_free(&iter->buf);
-	git_iterator_free(iter->fsiter);
-	git__free(iter);
-}
+	while (iter->loose_pos < iter->loose.length) {
+		const char *path = git_vector_get(&iter->loose, iter->loose_pos++);
 
-static int iter_packed(const char **out, refdb_fs_iter *iter)
-{
-	/* Move forward to the next entry */
-	while (!kh_exist(iter->h, iter->k)) {
-		iter->k++;
-		if (iter->k == kh_end(iter->h))
-			return GIT_ITEROVER;
+		if (loose_lookup(out, backend, path) == 0)
+			return 0;
+
+		giterr_clear();
 	}
 
-	*out = kh_key(iter->h, iter->k);
-	iter->k++;
+	while (iter->packed_pos < kh_end(packfile)) {
+		struct packref *ref = NULL;
 
-	return 0;
+		while (!kh_exist(packfile, iter->packed_pos)) {
+			iter->packed_pos++;
+			if (iter->packed_pos == kh_end(packfile))
+				return GIT_ITEROVER;
+		}
+
+		ref = kh_val(packfile, iter->packed_pos);
+		iter->packed_pos++;
+
+		if (ref->flags & PACKREF_SHADOWED)
+			continue;
+
+		if (iter->glob && p_fnmatch(iter->glob, ref->name, 0) != 0)
+			continue;
+
+		*out = git_reference__alloc(ref->name, &ref->oid, &ref->peel);
+		if (*out == NULL)
+			return -1;
+
+		return 0;
+	}
+
+	return GIT_ITEROVER;
 }
 
-static int iter_loose(const char **out, refdb_fs_iter *iter)
+static int refdb_fs_backend__iterator_next_name(
+	const char **out, git_reference_iterator *_iter)
 {
-	const git_index_entry *entry;
-	int retry;
-	git_strmap *packfile_refs;
-	refdb_fs_backend *backend = (refdb_fs_backend *) iter->parent.backend;
+	refdb_fs_iter *iter = (refdb_fs_iter *)_iter;
+	refdb_fs_backend *backend = (refdb_fs_backend *)iter->parent.db->backend;
+	git_strmap *packfile = backend->refcache.packfile;
 
-	packfile_refs = backend->refcache.packfile;
+	while (iter->loose_pos < iter->loose.length) {
+		const char *path = git_vector_get(&iter->loose, iter->loose_pos++);
 
-	do {
-		khiter_t pos;
-		if (git_iterator_current(&entry, iter->fsiter) < 0)
-			return -1;
+		if (git_strmap_exists(packfile, path))
+			continue;
 
-		git_buf_clear(&iter->buf);
-		if (!entry)
-			return GIT_ITEROVER;
+		*out = path;
+		return 0;
+	}
 
-		if (git_buf_printf(&iter->buf, "refs/%s", entry->path) < 0)
-			return -1;
+	while (iter->packed_pos < kh_end(packfile)) {
+		while (!kh_exist(packfile, iter->packed_pos)) {
+			iter->packed_pos++;
+			if (iter->packed_pos == kh_end(packfile))
+				return GIT_ITEROVER;
+		}
 
-		git_iterator_advance(NULL, iter->fsiter);
+		*out = kh_key(packfile, iter->packed_pos);
+		iter->packed_pos++;
 
-		/* Skip this one if we already listed it in packed */
-		pos = git_strmap_lookup_index(packfile_refs, git_buf_cstr(&iter->buf));
-		retry = 0;
-		if (git_strmap_valid_index(packfile_refs, pos) ||
-		    !git_reference_is_valid_name(git_buf_cstr(&iter->buf)))
-			retry = 1;
+		if (iter->glob && p_fnmatch(iter->glob, *out, 0) != 0)
+			continue;
 
-		*out = git_buf_cstr(&iter->buf);
-	} while (retry);
+		return 0;
+	}
 
-	return 0;
+	return GIT_ITEROVER;
 }
 
-static int iter_loose_setup(refdb_fs_iter *iter)
+static int refdb_fs_backend__iterator(
+	git_reference_iterator **out, git_refdb_backend *_backend, const char *glob)
 {
-	refdb_fs_backend *backend = (refdb_fs_backend *) iter->parent.backend;
+	refdb_fs_iter *iter;
+	refdb_fs_backend *backend;
+
+	assert(_backend);
+	backend = (refdb_fs_backend *)_backend;
 
-	git_buf_clear(&iter->buf);
-	if (git_buf_printf(&iter->buf, "%s/refs", backend->path) < 0)
+	if (packed_load(backend) < 0)
 		return -1;
 
-	return git_iterator_for_filesystem(&iter->fsiter, git_buf_cstr(&iter->buf), 0, NULL, NULL);
+	iter = git__calloc(1, sizeof(refdb_fs_iter));
+	GITERR_CHECK_ALLOC(iter);
+
+	if (glob != NULL)
+		iter->glob = git__strdup(glob);
+
+	iter->parent.next = refdb_fs_backend__iterator_next;
+	iter->parent.next_name = refdb_fs_backend__iterator_next_name;
+	iter->parent.free = refdb_fs_backend__iterator_free;
+
+	if (iter_load_loose_paths(backend, iter) < 0) {
+		refdb_fs_backend__iterator_free((git_reference_iterator *)iter);
+		return -1;
+	}
+
+	*out = (git_reference_iterator *)iter;
+	return 0;
 }
 
-static int refdb_fs_backend__next(const char **out, git_reference_iterator *_iter)
+static bool ref_is_available(
+	const char *old_ref, const char *new_ref, const char *this_ref)
 {
-	refdb_fs_iter *iter = (refdb_fs_iter *)_iter;
+	if (old_ref == NULL || strcmp(old_ref, this_ref)) {
+		size_t reflen = strlen(this_ref);
+		size_t newlen = strlen(new_ref);
+		size_t cmplen = reflen < newlen ? reflen : newlen;
+		const char *lead = reflen < newlen ? new_ref : this_ref;
+
+		if (!strncmp(new_ref, this_ref, cmplen) && lead[cmplen] == '/') {
+			return false;
+		}
+	}
 
-	if (iter->loose)
-		return iter_loose(out, iter);
+	return true;
+}
 
-	if (iter->k != kh_end(iter->h)) {
-		int error = iter_packed(out, iter);
-		if (error != GIT_ITEROVER)
-			return error;
-	}
+static int reference_path_available(
+	refdb_fs_backend *backend,
+	const char *new_ref,
+	const char* old_ref,
+	int force)
+{
+	struct packref *this_ref;
 
-	if (iter_loose_setup(iter) < 0)
+	if (packed_load(backend) < 0)
 		return -1;
-	iter->loose = 1;
 
-	return iter_loose(out, iter);
+	if (!force) {
+		int exists;
+
+		if (refdb_fs_backend__exists(&exists, (git_refdb_backend *)backend, new_ref) < 0)
+			return -1;
+
+		if (exists) {
+			giterr_set(GITERR_REFERENCE,
+				"Failed to write reference '%s': a reference with "
+				" that name already exists.", new_ref);
+			return GIT_EEXISTS;
+		}
+	}
+
+	git_strmap_foreach_value(backend->refcache.packfile, this_ref, {
+		if (!ref_is_available(old_ref, new_ref, this_ref->name)) {
+			giterr_set(GITERR_REFERENCE,
+				"The path to reference '%s' collides with an existing one", new_ref);
+			return -1;
+		}
+	});
+	
+	return 0;
 }
 
 static int loose_write(refdb_fs_backend *backend, const git_reference *ref)
@@ -695,8 +793,7 @@ static int loose_write(refdb_fs_backend *backend, const git_reference *ref)
 	/* Remove a possibly existing empty directory hierarchy
 	 * which name would collide with the reference name
 	 */
-	if (git_futils_rmdir_r(ref->name, backend->path,
-		GIT_RMDIR_SKIP_NONEMPTY) < 0)
+	if (git_futils_rmdir_r(ref->name, backend->path, GIT_RMDIR_SKIP_NONEMPTY) < 0)
 		return -1;
 
 	if (git_buf_joinpath(&ref_path, backend->path, ref->name) < 0)
@@ -956,37 +1053,40 @@ cleanup_memory:
 
 static int refdb_fs_backend__write(
 	git_refdb_backend *_backend,
-	const git_reference *ref)
+	const git_reference *ref,
+	int force)
 {
 	refdb_fs_backend *backend;
+	int error;
 
 	assert(_backend);
 	backend = (refdb_fs_backend *)_backend;
 
+	error = reference_path_available(backend, ref->name, NULL, force);
+	if (error < 0)
+		return error;
+
 	return loose_write(backend, ref);
 }
 
 static int refdb_fs_backend__delete(
 	git_refdb_backend *_backend,
-	const git_reference *ref)
+	const char *ref_name)
 {
 	refdb_fs_backend *backend;
-	git_repository *repo;
 	git_buf loose_path = GIT_BUF_INIT;
 	struct packref *pack_ref;
 	khiter_t pack_ref_pos;
-	int error = 0, pack_error;
+	int error = 0;
 	bool loose_deleted = 0;
 
 	assert(_backend);
-	assert(ref);
+	assert(ref_name);
 
 	backend = (refdb_fs_backend *)_backend;
-	repo = backend->repo;
 
 	/* If a loose reference exists, remove it from the filesystem */
-
-	if (git_buf_joinpath(&loose_path, repo->path_repository, ref->name) < 0)
+	if (git_buf_joinpath(&loose_path, backend->path, ref_name) < 0)
 		return -1;
 
 	if (git_path_isfile(loose_path.ptr)) {
@@ -1000,22 +1100,66 @@ static int refdb_fs_backend__delete(
 		return error;
 
 	/* If a packed reference exists, remove it from the packfile and repack */
+	error = packed_map_entry(&pack_ref, &pack_ref_pos, backend, ref_name);
+
+	if (error == GIT_ENOTFOUND)
+		return loose_deleted ? 0 : GIT_ENOTFOUND;
 
-	if ((pack_error = packed_map_entry(&pack_ref, &pack_ref_pos, backend, ref->name)) == 0) {
+	if (error == 0) {
 		git_strmap_delete_at(backend->refcache.packfile, pack_ref_pos);
 		git__free(pack_ref);
-
 		error = packed_write(backend);
 	}
 
-	if (pack_error == GIT_ENOTFOUND)
-		error = loose_deleted ? 0 : GIT_ENOTFOUND;
-	else
-		error = pack_error;
-
 	return error;
 }
 
+static int refdb_fs_backend__rename(
+	git_reference **out,
+	git_refdb_backend *_backend,
+	const char *old_name,
+	const char *new_name,
+	int force)
+{
+	refdb_fs_backend *backend;
+	git_reference *old, *new;
+	int error;
+
+	assert(_backend);
+	backend = (refdb_fs_backend *)_backend;
+
+	error = reference_path_available(backend, new_name, old_name, force);
+	if (error < 0)
+		return error;
+
+	error = refdb_fs_backend__lookup(&old, _backend, old_name);
+	if (error < 0)
+		return error;
+
+	error = refdb_fs_backend__delete(_backend, old_name);
+	if (error < 0) {
+		git_reference_free(old);
+		return error;
+	}
+
+	new = realloc(old, sizeof(git_reference) + strlen(new_name) + 1);
+	memcpy(new->name, new_name, strlen(new_name) + 1);
+
+	error = loose_write(backend, new);
+	if (error < 0) {
+		git_reference_free(new);
+		return error;
+	}
+
+	if (out) {
+		*out = new;
+	} else {
+		git_reference_free(new);
+	}
+
+	return 0;
+}
+
 static int refdb_fs_backend__compress(git_refdb_backend *_backend)
 {
 	refdb_fs_backend *backend;
@@ -1088,7 +1232,7 @@ static int setup_namespace(git_buf *path, git_repository *repo)
 	}
 
 	git_buf_printf(path, "refs/namespaces/%s/refs", end);
-	free(parts);
+	git__free(parts);
 
 	/* Make sure that the folder with the namespace exists */
 	if (git_futils_mkdir_r(git_buf_cstr(path), repo->path_repository, 0777) < 0)
@@ -1121,10 +1265,9 @@ int git_refdb_backend_fs(
 	backend->parent.exists = &refdb_fs_backend__exists;
 	backend->parent.lookup = &refdb_fs_backend__lookup;
 	backend->parent.iterator = &refdb_fs_backend__iterator;
-	backend->parent.next = &refdb_fs_backend__next;
-	backend->parent.iterator_free = &refdb_fs_backend__iterator_free;
 	backend->parent.write = &refdb_fs_backend__write;
 	backend->parent.delete = &refdb_fs_backend__delete;
+	backend->parent.rename = &refdb_fs_backend__rename;
 	backend->parent.compress = &refdb_fs_backend__compress;
 	backend->parent.free = &refdb_fs_backend__free;
 
diff --git a/src/refs.c b/src/refs.c
index 166669ef2..2b545954d 100644
--- a/src/refs.c
+++ b/src/refs.c
@@ -95,123 +95,15 @@ void git_reference_free(git_reference *reference)
 	if (reference->type == GIT_REF_SYMBOLIC)
 		git__free(reference->target.symbolic);
 
-	git__free(reference);
-}
-
-struct reference_available_t {
-	const char *new_ref;
-	const char *old_ref;
-	int available;
-};
-
-static int _reference_available_cb(const char *ref, void *data)
-{
-	struct reference_available_t *d;
-
-	assert(ref && data);
-	d = (struct reference_available_t *)data;
-
-	if (!d->old_ref || strcmp(d->old_ref, ref)) {
-		size_t reflen = strlen(ref);
-		size_t newlen = strlen(d->new_ref);
-		size_t cmplen = reflen < newlen ? reflen : newlen;
-		const char *lead = reflen < newlen ? d->new_ref : ref;
-
-		if (!strncmp(d->new_ref, ref, cmplen) && lead[cmplen] == '/') {
-			d->available = 0;
-			return -1;
-		}
-	}
-
-	return 0;
-}
-
-static int reference_path_available(
-	git_repository *repo,
-	const char *ref,
-	const char* old_ref)
-{
-	int error;
-	struct reference_available_t data;
-
-	data.new_ref = ref;
-	data.old_ref = old_ref;
-	data.available = 1;
-
-	error = git_reference_foreach(
-		repo, _reference_available_cb, (void *)&data);
-	if (error < 0)
-		return error;
-
-	if (!data.available) {
-		giterr_set(GITERR_REFERENCE,
-			"The path to reference '%s' collides with an existing one", ref);
-		return -1;
-	}
-
-	return 0;
-}
-
-/*
- * Check if a reference could be written to disk, based on:
- *
- *	- Whether a reference with the same name already exists,
- *	and we are allowing or disallowing overwrites
- *
- *	- Whether the name of the reference would collide with
- *	an existing path
- */
-static int reference_can_write(
-	git_repository *repo,
-	const char *refname,
-	const char *previous_name,
-	int force)
-{
-	git_refdb *refdb;
-
-	if (git_repository_refdb__weakptr(&refdb, repo) < 0)
-		return -1;
-
-	/* see if the reference shares a path with an existing reference;
-	 * if a path is shared, we cannot create the reference, even when forcing */
-	if (reference_path_available(repo, refname, previous_name) < 0)
-		return -1;
-
-	/* check if the reference actually exists, but only if we are not forcing
-	 * the rename. If we are forcing, it's OK to overwrite */
-	if (!force) {
-		int exists;
-
-		if (git_refdb_exists(&exists, refdb, refname) < 0)
-			return -1;
-
-		/* We cannot proceed if the reference already exists and we're not forcing
-		 * the rename; the existing one would be overwritten */
-		if (exists) {
-			giterr_set(GITERR_REFERENCE,
-				"A reference with that name (%s) already exists", refname);
-			return GIT_EEXISTS;
-		}
-	}
-
-	/* FIXME: if the reference exists and we are forcing, do we really need to
-	 * remove the reference first?
-	 *
-	 * Two cases:
-	 *
-	 *	- the reference already exists and is loose: not a problem, the file
-	 *	gets overwritten on disk
-	 *
-	 *	- the reference already exists and is packed: we write a new one as
-	 *	loose, which by all means renders the packed one useless
-	 */
+	if (reference->db)
+		GIT_REFCOUNT_DEC(reference->db, git_refdb__free);
 
-	return 0;
+	git__free(reference);
 }
 
 int git_reference_delete(git_reference *ref)
 {
-	return git_refdb_delete(ref->db, ref);
+	return git_refdb_delete(ref->db, ref->name);
 }
 
 int git_reference_lookup(git_reference **ref_out,
@@ -418,22 +310,24 @@ static int reference__create(
 	if (ref_out)
 		*ref_out = NULL;
 
-	if ((error = git_reference__normalize_name_lax(normalized, sizeof(normalized), name)) < 0 ||
-		(error = reference_can_write(repo, normalized, NULL, force)) < 0 ||
-		(error = git_repository_refdb__weakptr(&refdb, repo)) < 0)
+	error = git_reference__normalize_name_lax(normalized, sizeof(normalized), name);
+	if (error < 0)
+		return error;
+
+	error = git_repository_refdb__weakptr(&refdb, repo);
+	if (error < 0)
 		return error;
 
 	if (oid != NULL) {
 		assert(symbolic == NULL);
-		ref = git_reference__alloc(name, oid, NULL);
+		ref = git_reference__alloc(normalized, oid, NULL);
 	} else {
-		ref = git_reference__alloc_symbolic(name, symbolic);
+		ref = git_reference__alloc_symbolic(normalized, symbolic);
 	}
 
 	GITERR_CHECK_ALLOC(ref);
-	ref->db = refdb;
 
-	if ((error = git_refdb_write(refdb, ref)) < 0) {
+	if ((error = git_refdb_write(refdb, ref, force)) < 0) {
 		git_reference_free(ref);
 		return error;
 	}
@@ -530,76 +424,41 @@ int git_reference_rename(
 	unsigned int normalization_flags;
 	char normalized[GIT_REFNAME_MAX];
 	bool should_head_be_updated = false;
-	git_reference *result = NULL;
 	int error = 0;
 	int reference_has_log;
 
-	*out = NULL;
-
 	normalization_flags = ref->type == GIT_REF_SYMBOLIC ?
 		GIT_REF_FORMAT_ALLOW_ONELEVEL : GIT_REF_FORMAT_NORMAL;
 
 	if ((error = git_reference_normalize_name(
-			normalized, sizeof(normalized), new_name, normalization_flags)) < 0 ||
-		(error = reference_can_write(ref->db->repo, normalized, ref->name, force)) < 0)
+			normalized, sizeof(normalized), new_name, normalization_flags)) < 0)
 		return error;
 
-	/*
-	 * Create the new reference.
-	 */
-	if (ref->type == GIT_REF_OID) {
-		result = git_reference__alloc(new_name, &ref->target.oid, &ref->peel);
-	} else if (ref->type == GIT_REF_SYMBOLIC) {
-		result = git_reference__alloc_symbolic(new_name, ref->target.symbolic);
-	} else {
-		assert(0);
-	}
-
-	if (result == NULL)
-		return -1;
-
-	result->db = ref->db;
-
 	/* Check if we have to update HEAD. */
 	if ((error = git_branch_is_head(ref)) < 0)
-		goto on_error;
+		return error;
 
 	should_head_be_updated = (error > 0);
 
-	/* Now delete the old ref and save the new one. */
-	if ((error = git_refdb_delete(ref->db, ref)) < 0)
-		goto on_error;
-
-	/* Save the new reference. */
-	if ((error = git_refdb_write(ref->db, result)) < 0)
-		goto rollback;
+	if ((error = git_refdb_rename(out, ref->db, ref->name, new_name, force)) < 0)
+		return error;
 
 	/* Update HEAD it was poiting to the reference being renamed. */
-	if (should_head_be_updated && (error = git_repository_set_head(ref->db->repo, new_name)) < 0) {
+	if (should_head_be_updated &&
+		(error = git_repository_set_head(ref->db->repo, new_name)) < 0) {
 		giterr_set(GITERR_REFERENCE, "Failed to update HEAD after renaming reference");
-		goto on_error;
+		return error;
 	}
 
 	/* Rename the reflog file, if it exists. */
 	reference_has_log = git_reference_has_log(ref);
-	if (reference_has_log < 0) {
-		error = reference_has_log;
-		goto on_error;
-	}
-	if (reference_has_log && (error = git_reflog_rename(ref, new_name)) < 0)
-		goto on_error;
+	if (reference_has_log < 0)
+		return reference_has_log;
 
-	*out = result;
-
-	return error;
-
-rollback:
-	git_refdb_write(ref->db, ref);
-
-on_error:
-	git_reference_free(result);
+	if (reference_has_log && (error = git_reflog_rename(ref, new_name)) < 0)
+		return error;
 
-	return error;
+	return 0;
 }
 
 int git_reference_resolve(git_reference **ref_out, const git_reference *ref)
@@ -623,14 +482,69 @@ int git_reference_foreach(
 	void *payload)
 {
 	git_reference_iterator *iter;
-	const char *name;
+	git_reference *ref;
 	int error;
 
 	if (git_reference_iterator_new(&iter, repo) < 0)
 		return -1;
 
-	while ((error = git_reference_next(&name, iter)) == 0) {
-		if (callback(name, payload)) {
+	while ((error = git_reference_next(&ref, iter)) == 0) {
+		if (callback(ref, payload)) {
+			error = GIT_EUSER;
+			goto out;
+		}
+	}
+
+	if (error == GIT_ITEROVER)
+		error = 0;
+
+out:
+	git_reference_iterator_free(iter);
+	return error;
+}
+
+int git_reference_foreach_name(
+	git_repository *repo,
+	git_reference_foreach_name_cb callback,
+	void *payload)
+{
+	git_reference_iterator *iter;
+	const char *refname;
+	int error;
+
+	if (git_reference_iterator_new(&iter, repo) < 0)
+		return -1;
+
+	while ((error = git_reference_next_name(&refname, iter)) == 0) {
+		if (callback(refname, payload)) {
+			error = GIT_EUSER;
+			goto out;
+		}
+	}
+
+	if (error == GIT_ITEROVER)
+		error = 0;
+
+out:
+	git_reference_iterator_free(iter);
+	return error;
+}
+
+int git_reference_foreach_glob(
+	git_repository *repo,
+	const char *glob,
+	git_reference_foreach_name_cb callback,
+	void *payload)
+{
+	git_reference_iterator *iter;
+	const char *refname;
+	int error;
+
+	if (git_reference_iterator_glob_new(&iter, repo, glob) < 0)
+		return -1;
+
+	while ((error = git_reference_next_name(&refname, iter)) == 0) {
+		if (callback(refname, payload)) {
 			error = GIT_EUSER;
 			goto out;
 		}
@@ -651,22 +565,28 @@ int git_reference_iterator_new(git_reference_iterator **out, git_repository *rep
 	if (git_repository_refdb__weakptr(&refdb, repo) < 0)
 		return -1;
 
-	return git_refdb_iterator(out, refdb);
+	return git_refdb_iterator(out, refdb, NULL);
 }
 
-int git_reference_iterator_glob_new(git_reference_iterator **out, git_repository *repo, const char *glob)
+int git_reference_iterator_glob_new(
+	git_reference_iterator **out, git_repository *repo, const char *glob)
 {
 	git_refdb *refdb;
 
 	if (git_repository_refdb__weakptr(&refdb, repo) < 0)
 		return -1;
 
-	return git_refdb_iterator_glob(out, refdb, glob);
+	return git_refdb_iterator(out, refdb, glob);
 }
 
-int git_reference_next(const char **out, git_reference_iterator *iter)
+int git_reference_next(git_reference **out, git_reference_iterator *iter)
 {
-	return git_refdb_next(out, iter);
+	return git_refdb_iterator_next(out, iter);
+}
+
+int git_reference_next_name(const char **out, git_reference_iterator *iter)
+{
+	return git_refdb_iterator_next_name(out, iter);
 }
 
 void git_reference_iterator_free(git_reference_iterator *iter)
@@ -693,7 +613,7 @@ int git_reference_list(
 	if (git_vector_init(&ref_list, 8, NULL) < 0)
 		return -1;
 
-	if (git_reference_foreach(
+	if (git_reference_foreach_name(
 			repo, &cb__reflist_add, (void *)&ref_list) < 0) {
 		git_vector_free(&ref_list);
 		return -1;
@@ -991,34 +911,6 @@ int git_reference__update_terminal(
 	return reference__update_terminal(repo, ref_name, oid, 0);
 }
 
-int git_reference_foreach_glob(
-	git_repository *repo,
-	const char *glob,
-	git_reference_foreach_cb callback,
-	void *payload)
-{
-	git_reference_iterator *iter;
-	const char *name;
-	int error;
-
-	if (git_reference_iterator_glob_new(&iter, repo, glob) < 0)
-		return -1;
-
-	while ((error = git_reference_next(&name, iter)) == 0) {
-		if (callback(name, payload)) {
-			error = GIT_EUSER;
-			goto out;
-		}
-	}
-
-	if (error == GIT_ITEROVER)
-		error = 0;
-
-out:
-	git_reference_iterator_free(iter);
-	return error;
-}
-
 int git_reference_has_log(
 	git_reference *ref)
 {
diff --git a/src/remote.c b/src/remote.c
index 4c1b39818..943b72bb7 100644
--- a/src/remote.c
+++ b/src/remote.c
@@ -1233,31 +1233,23 @@ static int update_branch_remote_config_entry(
 }
 
 static int rename_one_remote_reference(
-	git_repository *repo,
-	const char *reference_name,
+	git_reference *reference,
 	const char *old_remote_name,
 	const char *new_remote_name)
 {
 	int error = -1;
 	git_buf new_name = GIT_BUF_INIT;
-	git_reference *reference = NULL;
-	git_reference *newref = NULL;
 
 	if (git_buf_printf(
 		&new_name,
 		GIT_REFS_REMOTES_DIR "%s%s",
 		new_remote_name,
-		reference_name + strlen(GIT_REFS_REMOTES_DIR) + strlen(old_remote_name)) < 0)
+		reference->name + strlen(GIT_REFS_REMOTES_DIR) + strlen(old_remote_name)) < 0)
 			return -1;
 
-	if (git_reference_lookup(&reference, repo, reference_name) < 0)
-		goto cleanup;
-
-	error = git_reference_rename(&newref, reference, git_buf_cstr(&new_name), 0);
+	error = git_reference_rename(NULL, reference, git_buf_cstr(&new_name), 0);
 	git_reference_free(reference);
 
-cleanup:
-	git_reference_free(newref);
 	git_buf_free(&new_name);
 	return error;
 }
@@ -1267,46 +1259,28 @@ static int rename_remote_references(
 	const char *old_name,
 	const char *new_name)
 {
-	git_vector refnames;
 	int error = -1;
-	unsigned int i;
-	char *name;
-	const char *refname;
+	git_reference *ref;
 	git_reference_iterator *iter;
 
-	if (git_vector_init(&refnames, 8, NULL) < 0)
-		return -1;
-
 	if (git_reference_iterator_new(&iter, repo) < 0)
-		goto cleanup;
+		return -1;
 
-	while ((error = git_reference_next(&refname, iter)) == 0) {
-		if (git__prefixcmp(refname, GIT_REFS_REMOTES_DIR))
+	while ((error = git_reference_next(&ref, iter)) == 0) {
+		if (git__prefixcmp(ref->name, GIT_REFS_REMOTES_DIR))
 			continue;
 
-		if ((error = git_vector_insert(&refnames, git__strdup(refname))) < 0)
-			break;
-
+		if ((error = rename_one_remote_reference(ref, old_name, new_name)) < 0) {
+			git_reference_iterator_free(iter);
+			return error;
+		}
 	}
 
 	git_reference_iterator_free(iter);
-	if (error == GIT_ITEROVER)
-		error = 0;
-	else
-		goto cleanup;
 
-	git_vector_foreach(&refnames, i, name) {
-		if ((error = rename_one_remote_reference(repo, name, old_name, new_name)) < 0)
-			goto cleanup;
-	}
-
-	error = 0;
-cleanup:
-	git_vector_foreach(&refnames, i, name) {
-		git__free(name);
-	}
+	if (error == GIT_ITEROVER)
+		return 0;
 
-	git_vector_free(&refnames);
 	return error;
 }
 
diff --git a/src/repository.c b/src/repository.c
index 28505e822..2e7a334c9 100644
--- a/src/repository.c
+++ b/src/repository.c
@@ -1473,12 +1473,14 @@ static int at_least_one_cb(const char *refname, void *payload)
 
 static int repo_contains_no_reference(git_repository *repo)
 {
-	int error = git_reference_foreach(repo, at_least_one_cb, NULL);
+	int error = git_reference_foreach_name(repo, &at_least_one_cb, NULL);
 
 	if (error == GIT_EUSER)
 		return 0;
+
 	if (!error)
 		return 1;
+
 	return error;
 }
 
diff --git a/src/submodule.c b/src/submodule.c
index f4fbcd35a..16114d8ac 100644
--- a/src/submodule.c
+++ b/src/submodule.c
@@ -1143,9 +1143,7 @@ static int load_submodule_config_from_index(
 		(error = git_iterator_for_index(&i, index, 0, NULL, NULL)) < 0)
 		return error;
 
-	error = git_iterator_current(&entry, i);
-
-	while (!error && entry != NULL) {
+	while (!(error = git_iterator_advance(&entry, i))) {
 
 		if (S_ISGITLINK(entry->mode)) {
 			error = submodule_load_from_index(repo, entry);
@@ -1158,10 +1156,11 @@ static int load_submodule_config_from_index(
 			if (strcmp(entry->path, GIT_MODULES_FILE) == 0)
 				git_oid_cpy(gitmodules_oid, &entry->oid);
 		}
-
-		error = git_iterator_advance(&entry, i);
 	}
 
+	if (error == GIT_ITEROVER)
+		error = 0;
+
 	git_iterator_free(i);
 
 	return error;
@@ -1183,9 +1182,7 @@ static int load_submodule_config_from_head(
 		return error;
 	}
 
-	error = git_iterator_current(&entry, i);
-
-	while (!error && entry != NULL) {
+	while (!(error = git_iterator_advance(&entry, i))) {
 
 		if (S_ISGITLINK(entry->mode)) {
 			error = submodule_load_from_head(repo, entry->path, &entry->oid);
@@ -1199,10 +1196,11 @@ static int load_submodule_config_from_head(
 				git_oid_iszero(gitmodules_oid))
 				git_oid_cpy(gitmodules_oid, &entry->oid);
 		}
-
-		error = git_iterator_advance(&entry, i);
 	}
 
+	if (error == GIT_ITEROVER)
+		error = 0;
+
 	git_iterator_free(i);
 	git_tree_free(head);
 
diff --git a/src/tag.c b/src/tag.c
index ecf3876cb..71f4c1eb1 100644
--- a/src/tag.c
+++ b/src/tag.c
@@ -440,7 +440,7 @@ int git_tag_foreach(git_repository *repo, git_tag_foreach_cb cb, void *cb_data)
 	data.cb_data = cb_data;
 	data.repo = repo;
 
-	return git_reference_foreach(repo, &tags_cb, &data);
+	return git_reference_foreach_name(repo, &tags_cb, &data);
 }
 
 typedef struct {