Timeline displays edits to state events incorrectly

[richvdh]

Steps to reproduce

Suppose I send an m.room.topic event with this content:

{
  "topic":"spam spam spam spam", 
  "m.new_content": {"topic": "normal topic"},
  "m.relates_to": {"rel_type":"m.replace","event_id":"<previous topic event>"}
}

This changes the topic of the room to spam spam spam spam. However, the timeline replaces the previous topic change event with:

(it doesn't even label it (edited) or allow you to view the edit history).

I feel like we probably shouldn't process edits of state events (or indeed anything that's not a (possibly encrypted) m.room.message).

Outcome

What did you expect?

The timeline should reflect reality. Since there were two separate topic changes, I think these should be shown as separate events, and the m.replace relation should be ignored.

What happened instead?

The timeline showed a state change that never happened

Operating system

No response

Browser information

No response

URL for webapp

develop.element.io

Application version

Element version: f46a6f2-react-70cdd57a5c61-js-540514c805ea Olm version: 3.2.8

Homeserver

No response

Will you send logs?

No

[t3chguy]

I feel like we probably shouldn't process edits of state events (or indeed anything that's not a (possibly encrypted) m.room.message).

Made a PR which ignores edits on state events, the latter would not match the MSC so erred away from it

[richvdh]

Made a PR which ignores edits on state events,

brilliant, thanks for jumping on this so quickly.

the latter would not match the MSC so erred away from it

I don't think the MSC is currently particularly clear on this point. We need to define what the expected behaviour actually is. Your interpretation is certainly valid, though, so I think I'll make the MSC match it.

Out of interest though: would we be able to tell the difference? In other words, does Element-web have any support for showing events in the timeline which aren't any of (a) a state event, (b) an m.room.message, (c) an encrypted m.room.message ?

[t3chguy]

I don't think the MSC is currently particularly clear on this point. We need to define what the expected behaviour actually is. Your interpretation is certainly valid, though, so I think I'll make the MSC match it.

The MSC explicitly says not state events, but yes you're right in that it doesn't specify an allow set

Only non-state events for now.

• https://github.com/uhoreg/matrix-doc/blob/aggregations-edits/proposals/2676-message-editing.md#edge-cases

Out of interest though: would we be able to tell the difference? In other words, does Element-web have any support for showing events in the timeline which aren't any of (a) a state event, (b) an m.room.message, (c) an encrypted m.room.message ?

Polls can be edited via the UI even, they're of type org.matrix.msc3381.poll.start

Editing stickers is probably valid and functional too (m.sticker) - but EW has no UI to do such

[richvdh]

The MSC explicitly says not state events, but yes you're right in that it doesn't specify an allow set

yeah, tbh I'm treating that "edge cases" section as "a bunch of stuff we haven't yet defined". But fine, let's do that.

Polls, stickers.

That's super-helpful, thanks.

[richvdh]

I'm not entirely convinced this is fixed. It's better, but not great. See #22280