@@ -46,0 +49,4 @@
+/// the new room ID.
+///
+/// See: https://github.com/matrix-org/matrix-spec-proposals/pull/4168
+async fn msc4168_update_parent_spaces(

@@ -69,0 +270,4 @@
+	if !services.config.allow_unstable_room_versions
+		&& UNSTABLE_ROOM_VERSIONS.contains(&body.new_version)
+	{
+		return Err(Error::BadRequest(

@@ -85,3 +293,1 @@
-	// Note that this does internally call the policy server with a fake room ID,
-	// which may not be good?
-	let tombstone_test_result = services
+	// Check tombstone permission by attempting to create (but not send) the event.

@@ -230,0 +377,4 @@
+		// NOTE: Using a hardcoded room ID for the temporary mutex means only one room
+		// can be created at a time. This is actually beneficial, as it reduces the
+		// risk of concurrent in-flight collisions.
+		services.rooms.state.mutex.lock("!new-room").await

@@ -46,0 +149,4 @@
+
+	// In rooms that reference the old room via m.space.parent events...
+	// NOTE: Doing that would be expensive. We'll instead fetch rooms which the
+	// space claims are children.