Upgrading a room can orphan it from its space

[robintown]

Steps to reproduce

1. As User A, create a space
2. Add Room A to the space
3. Invite User B to the space and Room A
4. Make User B an admin in Room A, but not the space
5. As User B, upgrade Room A to Room B
6. Invite User C to the space and Room B

For context, while this is an uncommon scenario, it's already happened in the Element Corp. space.

Outcome

What did you expect?

User C should see Room B listed as a child of the space.

What happened instead?

To User C, Room B appears as an orphaned room, since the space actually only lists Room A as a child, and User C has no way to know about the upgrade.

Well, that's not entirely true. User C could find out about the upgrade by looking at the room creation event. But if the room were upgraded twice rather than once, this would still not be enough information to connect the upgraded room back to Room A.

I'm not sure how this could be resolved. Perhaps spec changes?

Operating system

NixOS unstable

Browser information

Firefox 97.0.1

URL for webapp

develop.element.io

Application version

Element version: 95de708f4ee7-react-1a6134e441ba-js-53aa34fba57c Olm version: 3.2.8

Homeserver

Synapse 1.52.0

Will you send logs?

No

[t3chguy]

Well, that's not entirely true. User C could find out about the upgrade by looking at the room creation event. But if the room were upgraded twice rather than once, this would still not be enough information to connect the upgraded room back to Room A.

This also can be abused, I could create NefariousRoom which claims to be an upgrade of MatrixHQ and now anyone joining the room would see it in the Matrix Community space wrongly

[ericdecanini]

Slightly related: There's confusion even on Android about what should happen during a room upgrade with regards to how the old room shows within its space.

element-hq/element-android#6411

"The pre-upgraded room would disappear only when the upgrade invite is accepted"
I think we should aim for this behaviour on all platforms. What do you think @robintown?

[robintown]

@ericdecanini That certainly sounds a bit more reasonable that what currently happens

[Mikaela]

I have a somewhat related spec issue open on rewriting restricted join rules when a room/Space is upgraded. matrix-org/matrix-spec#1072