MSC2214: Joining upgraded private rooms

[turt2live]

Rendered

Related issues:

• https://github.com/matrix-org/matrix-doc/issues/1864 ("solved" by this)
• https://github.com/matrix-org/matrix-doc/issues/1941 (related by subject)

[ara4n]

disappointing

[turt2live]

@ara4n and now? 😇

[ara4n]

much better ;)

in terms of the actual MSC: it's probably an obvious question, but: why clone over as m.room.previous_member events at all? why not make them m.room.members?

[turt2live]

Because of https://github.com/matrix-org/matrix-doc/pull/2214/files#diff-3ca6ba2dd370c7a964783f11e300128eR107-R111

The TLDR is that the auth rules get difficult because we can't really do auth rules across multiple rooms yet, so it would be possible for someone to craft a room which automatically joins everyone.

Edit: and as for just spamming invites: this is also mentioned in the proposal as undesirable notifications.

[turt2live]

TODO: Incorporate this rationale into the proposal somewhere (and surrounding discussion)

fwiw the overarching idea is that servers just attempt to join rooms and expect it to fail, rather than have them spend a bunch of time adding if statements for suppressing notifications (which would also need to be added to every client), handling the invite differently, etc. It puts the burden of figuring out if a user can join on the server which did the upgrade (and any other resident servers after the fact), letting the client implementations need no changes.