iterator: advance the tree iterator smartly

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

While advancing the tree iterator, if we advance over things that
we aren't interested in, then call `current`.  Which may *itself*
call advance.

Error: stack overflow.

src/iterator.c

@@ -640,74 +640,32 @@ static int tree_iterator__current_internal(
 	return 0;
 }
 
-static int tree_iterator__advance(
+static int tree_iterator__advance_into_internal(git_iterator *self)
-	const git_index_entry **out, git_iterator *self);
-
-static int tree_iterator__current(
-	const git_index_entry **out, git_iterator *self)
-{
-	const git_index_entry *entry = NULL;
-	iterator_pathlist__match_t m;
-	int error;
-
-	do {
-		if ((error = tree_iterator__current_internal(&entry, self)) < 0)
-			return error;
-
-		if (self->pathlist.length) {
-			m = iterator_pathlist__match(
-				self, entry->path, strlen(entry->path));
-
-			if (m != ITERATOR_PATHLIST_MATCH) {
-				if ((error = tree_iterator__advance(&entry, self)) < 0)
-					return error;
-
-				entry = NULL;
-			}
-		}
-	} while (!entry);
-
-	if (out)
-		*out = entry;
-
-	return error;
-}
-
-static int tree_iterator__advance_into(
-	const git_index_entry **entry, git_iterator *self)
 {
 	int error = 0;
 	tree_iterator *ti = (tree_iterator *)self;
 
-	iterator__clear_entry(entry);
-
 	if (tree_iterator__at_tree(ti))
 		error = tree_iterator__push_frame(ti);
 
-	if (!error && entry)
-		error = tree_iterator__current(entry, self);
-
 	return error;
 }
 
-static int tree_iterator__advance(
+static int tree_iterator__advance_internal(git_iterator *self)
-	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 (!iterator__has_been_accessed(ti))
-		return tree_iterator__current(entry, self);
+		return 0;
 
 	if (iterator__do_autoexpand(ti) && iterator__include_trees(ti) &&
 		tree_iterator__at_tree(ti))
-		return tree_iterator__advance_into(entry, self);
+		return tree_iterator__advance_into_internal(self);
 
 	if (ti->path_has_filename) {
 		git_buf_rtruncate_at_char(&ti->path, '/');
@@ -725,7 +683,63 @@ static int tree_iterator__advance(
 
 	/* deal with include_trees / auto_expand as needed */
 	if (!iterator__include_trees(ti) && tree_iterator__at_tree(ti))
-		return tree_iterator__advance_into(entry, self);
+		return tree_iterator__advance_into_internal(self);
+
+	return 0;
+}
+
+static int tree_iterator__current(
+	const git_index_entry **out, git_iterator *self)
+{
+	const git_index_entry *entry = NULL;
+	iterator_pathlist__match_t m;
+	int error;
+
+	do {
+		if ((error = tree_iterator__current_internal(&entry, self)) < 0)
+			return error;
+
+		if (self->pathlist.length) {
+			m = iterator_pathlist__match(
+				self, entry->path, strlen(entry->path));
+
+			if (m != ITERATOR_PATHLIST_MATCH) {
+				if ((error = tree_iterator__advance_internal(self)) < 0)
+					return error;
+
+				entry = NULL;
+			}
+		}
+	} while (!entry);
+
+	if (out)
+		*out = entry;
+
+	return error;
+}
+
+static int tree_iterator__advance(
+	const git_index_entry **entry, git_iterator *self)
+{
+	int error = tree_iterator__advance_internal(self);
+
+	iterator__clear_entry(entry);
+
+	if (error < 0)
+		return error;
+
+	return tree_iterator__current(entry, self);
+}
+
+static int tree_iterator__advance_into(
+	const git_index_entry **entry, git_iterator *self)
+{
+	int error = tree_iterator__advance_into_internal(self);
+
+	iterator__clear_entry(entry);
+
+	if (error < 0)
+		return error;
 
 	return tree_iterator__current(entry, self);
 }