Show edited/moved marker on messages

[gnprice]

When a message has been edited or moved, Zulip web shows this with a small "EDITED" or "MOVED" marker. This can be important for understanding a conversation; we should do either the same thing or another way of conveying the same information.

The Help Center describes this feature on the following page:
https://zulip.com/help/view-a-messages-edit-history
though that page also covers showing the details of the edits or moves, which is a separate issue #531.

UI design

See first comments below, and see this later chat thread:
https://chat.zulip.org/#narrow/stream/48-mobile/topic/check-x.20icons.20in.20left.20margin/near/1908288

Implementation

We don't currently store the information of whether and how a message has been edited or moved. The first phase of work on this issue will be to start storing and maintaining that information. This will involve adding a field to the Message class, and then updating that field as appropriate in response to events.

Concretely, this field should look like MessageEditState edited; where MessageEditState is an enum with three values: none, moved, and edited. In other words it will store only the information needed to control the edited/moved marker; storing the full edit history is out of scope for this issue (and will be left for #531).

After that we can start showing the information in the UI.

Related issues

These related features are all out of scope for this issue:

• compose: Support editing an already-sent message #126
• Support moving a message between topics and streams #530
• Show edit history of a message #531

(The details of the edits or moves can be important information too, but for a lot of purposes just the fact that the message was edited or moved, or the ability to confirm that it wasn't, is very helpful.)

Note that some of these have the "Post-launch" milestone — those are things we expect to get to much later than this issue.

[terpimost]

The main idea was to use the left gutter to put a small icon of edited or moved + allow to swipe/drag the message horizontally to reveal full label:

This design isn't final, but let me know what do you think about interaction. Would it be hard to do or not?

[gnprice]

Interesting, thanks.

I think that gesture should be doable from the implementation side. There may not be anything drop-in we can use for the whole swipe interaction; but we can give each message a GestureDetector that responds to onHorizontalDragStart and its update/end/etc. friends, and build the interaction out of those pieces.

(There is a drop-in implementation for "drag". But that's for a gesture that starts by long-pressing a thing to pick it up; I don't think it's designed for this use case.)

[fizy069]

Hi, I've been working on this issue and I've partially implemented the Edit marker, using Greg's suggestion (GestureDetector responding to onHorizontalDragStart).
I'd like to work on the UI and complete the implementation, it would be great if you could assign the issue to me.

This is how it looks so far.

[gnprice]

For ease of reference: here's the spot in @terpimost's Figma design that I think corresponds to the screenshot he posted above:
https://www.figma.com/file/1JTNtYo9memgW7vV6d0ygq/Zulip-Mobile?node-id=538-21662
(That screen for "edited", and the next one to the right for "moved".)