Leaving a room as a group admin breaks the group roomlist

[tari]

Description

As a group admin, leaving a room that is associated with the group causes it to appear incorrectly for all users. This was originally reported as an Element bug (element-hq/element-web#15375), but from inspecting the API responses this seems like it's a Synapse issue.

Steps to reproduce

• Create a group +foo:example.com
• Create the room #foo-offtopic:example.com and add it to +foo:example.com
• Leave #foo-offtopic:example.com

All users (including yourself) will now continue to see the room via GroupRoomServlet requests, but lacking any room information- it has no name or alias (even if published) so cannot be joined.

For instance, before leaving the room, the object returned looks like this (real response, lightly anonymized):

{
  "room_id":"!xCfjIbkGyBzlFQmuBg:nltrix.net",
  "num_joined_members":18,
  "m.federate":true,
  "name":"Some Room",
  "topic":"Topic goes here",
  "canonical_alias":"#someroom:taricorp.net",
  "world_readable":false,
  "guest_can_join":false,
  "is_public":true
},

After I leave the room, the group room response contains this room like this:

{
  room_id: "!xCfjIbkGyBzlFQmuBg:nltrix.net",
  num_joined_members: 0,
  is_public: true
}

Attempting to join the room in Element from the group's room list fails, and other users report the same behavior. Rejoining the room via its canonical alias works as expected.

Version information

• Homeserver: taricorp.net
• Version: 1.25.0
• Install method: nixos package
• Platform: NixOS Linux, x86 virtual machine

[anoadragon453]

Thank you for your report.

Groups in their current form are known to be buggy, and are due to be completely replaced by Matrix Spaces soon. As such this is unlikely to get fixed before that lands.

[NonstickAtom785]

How is that supposed to function? Will you still be able to see old history? And also will the bridges be affected? Will they still be a thing in Matrix Spaces? (Our entire group is bridged to a discord server.)

[tari]

MSC1772 reconsiders the concepts of the existing groups API in terms of rooms that look a little different. It doesn't have any bearing on rooms that are not themselves groups (not entirely true; there are provisions for a room to declare its membership in a group, but that doesn't affect the room's functioning), so there should be no meaningful change beyond community identifiers as they currently exist (+foo:example.com) becoming obsolete.

[clokep]

Communities/groups are being removed, see #11584.