Logic for auto creating auto join rooms is brittle.

[erikjohnston]

synapse/synapse/handlers/register.py

Lines 606 to 620 in 6c749c5

	# try to create the room if we're the first real user on the server. Note
	# that an auto-generated support or bot user is not a real user and will never be
	# the user to create the room
	should_auto_create_rooms = False
	if (
	self.hs.config.registration.autocreate_auto_join_rooms
	and await self.store.is_real_user(user_id)
	):
	count = await self.store.count_real_users()
	should_auto_create_rooms = count == 1
	if should_auto_create_rooms:
	await self._create_and_join_rooms(user_id)
	else:
	await self._join_rooms(user_id)

Problems include:

1. If auto join is enabled after the first real user is created.
2. Adding bots or support users will skip creating room, but will still try and join

We should change this to create the room if the room doesn't already exist, or something like that.

[vemmos]

Hey! Can you explain the scenario a bit ?