Local alias will not transfer on room upgrade if the upgrader is not the one who sent it #6842
Description
While transferring of local aliases on room upgrade is implemented, it will fail if the person upgrading the room was not the person who originally sent the alias.
MSC2432 improves things here a bit in that it will allow people will sufficient room permissions to remove m.room.alias events, specifically:
DELETE /_matrix/client/r0/directory/room/{roomAlias}: in this case, currently Synapse restricts its use to the user that created the alias, and server admins.It is proposed to extend this to local users who have a power-level sufficient to send an m.room.canonical_alias event in the room that the alias currently points to.
Although technically one can configure a room in a way where you can send m.room.tombstone events, but not have permission to modify aliases. In that case perhaps you aren't allowed to upgrade a room?
Changing the mapping can be specially done by the homeserver during a room upgrade (ignoring the sender here). We can only do this for local aliases of course.
Note to self: we need to be careful that with room admins able to delete aliases, that the room upgrade code won't remove all the aliases in the room, while simultaneously only being able to transfer the local ones. Remote aliases should be transferred when a user on a remote server joins the upgraded room.