If the last admin of a room departs, and thus the room no longer has any admins within it, we "freeze" the room. Freezing a room means that the power level required to do anything in the room (sending messages, inviting others etc) will require power level 100.
At the moment, an admin can come back and unfreeze the room manually. The plan is to eventually make unfreezing of the room automatic on admin rejoin, though that will be in a separate PR.
This *could* work in mainline, however if the admin who leaves is on a homeserver without this functionality, then the room isn't frozen. I imagine this would probably be pretty confusing to people. Part of this feature was allowing Synapse modules to send events, which has been implemented in mainline at https://github.com/matrix-org/synapse/pull/8479, and cherry-picked to the `dinsic` fork in 62c7b10. The actual freezing logic has been implemented here in the RoomAccessRules module.
Swap these calls around, as the check for changing `restricted` to `unrestricted` will actually change `self.restricted_room` to an unrestricted room.
Do that last, instead of first. Additionally add a comment with a warning.
This PR switches several conditions regarding room access rules to check against the status of the room's inclusion in the public room list instead of its join rules.
The code includes a snapshot of https://github.com/matrix-org/synapse/pull/8292, which will likely change in time and need merging in again.
This PR modifies the `RoomAccessRules` module, an implementation of `ThirdPartyEventRules`, to both:
* Modify the default power levels when creating a room to set:
- `invite` to be minimum PL50
- `state_default` to be minimum PL100
* Enforce this when creating the room.
