Synapse does not apply edits to events other than m.room.message

[richvdh]

MSC2676 says:

Whenever a homeserver would return an event via the Client-Server API, it should check for any valid, applicable m.replace event, and if one is found, it should first modify the content of the original event according to the m.new_content of the most recent edit.

It also gives a comprehensive list of what comprises a "valid" edit event.

Synapse does this, but only where the events are of type m.room.message. This is incorrect: it should also do so for other event types. Examples include polls (org.matrix.msc3381.poll.start), which can be edited via the Element UI, and stickers (m.sticker), which cannot be edited via the UI but can via the API.

This is closely related to #12503, but that concerns aggregations, whereas this issue is about updating the content of the original event.

[alariej]

I came across this issue while doing tests on matrix.org. As far as I can tell, Synapse doesn't even seem to "modify the content of the original event according to the m.new_content of the most recent edit.", even for m.room.message events. The original message content does not get modified after one or even several edits. Below are the message objects from a test I just did on matrix.org. The message was created and edited in a fresh non-encrypted private room using Element Web. After editing the message, I logged out, refreshed the browser, and logged back in to make sure the events were fetched again from the server.

Original message, before and after editing:

content:
  body: "hi"
  msgtype: "m.text"
  org.matrix.msc1767.text: "hi"
event_id: "$PbrLqfPm7MBDHLZd5gVREn3VA8UyFc8qb9220xiKYlw"
origin_server_ts: 1665067355108
sender: "@xyz:matrix.org"
type: "m.room.message"

Message created by editing:

content: 
  body: " * hi hi"
  msgtype: "m.text"
  org.matrix.msc1767.text: " * hi hi"
  m.new_content: 
    body: "hi hi"
    msgtype: "m.text"
    org.matrix.msc1767.text: "hi hi"
  m.relates_to: 
    event_id: "$PbrLqfPm7MBDHLZd5gVREn3VA8UyFc8qb9220xiKYlw"
    rel_type: "m.replace"
event_id: "$rOEXMZKBNp8iYoBcSvdOFIE7bAqVVpJGLhc68ENPLw8"
origin_server_ts: 1665067377760
sender: "@xyz:matrix.org"
type: "m.room.message"

I guess this would not get picked up by users as Element will anyway display the edited content of messages, but I'm wondering if something has changed in the protocol or implementation since this issue was opened. Or am I missing something completely obvious here?

[clokep]

As of today, the correct behavior should be applied, but only for m.room.message events. How are you requesting the event?

[alariej]

Via the sync API.

[clokep]

Via the sync API.

Bundled aggregations are only returned if the result is limited, see here:

Whenever an m.replace is to be bundled with an event as above, the server should also modify the content of the original event according to the m.new_content of the most recent replacement event (determined as above).

You can then see here when aggregations are bundled:

[GET /sync](https://spec.matrix.org/v1.4/client-server-api/#get_matrixclientv3sync) when the relevant section has a limited value of true.

[alariej]

Oh right, I had missed the point with the "limited". Not quite sure about the logic of it, but in any case, thanks for the info!

[clokep]

See #14252.

[clokep]

Hm actually I think this was fixed by #15193 to no longer apply edits.