Unnoticed messages in the chat noticed on another device

[iequidoo]

Steps to reproduce (Core v2.35.0):

• Have a 1st device offline
• Receive a lot of messages in some chat
• Read the last screen of messages by scrolling to the bottom of the chat (there's a button in the UIs for that) on the 2nd device
• Bring the 1st device online
• See notifications and unnoticed messages ("badge counter") which won't be fixed until you e.g. open the chat and scroll to the bottom on the 1st device as well

Note that if the 1st device is online, the notifications are removed because Session::sync_seen_flags() emits MsgsNoticed, but unnoticed messages persist.

Suggested fix: when a seen message is received or a \Seen IMAP flag arrives for a message, mark all preceding (by timestamp_sort) chat messages as noticed and emit MsgsNoticed. EDIT: MsgsNoticed should only be emitted if no fresh messages remain, otherwise it removes useful notifications in the UIs.

There was #6415, but that fix is incomplete because it only emits the event. Tests from there can be reused though, but also there should be a test checking a number of fresh messages in the chat (ChatId::get_fresh_msg_cnt()).

[Hocuri]

Suggested fix: when a seen message is received or a \Seen IMAP flag arrives for a message, mark all preceding (by timestamp_sort) chat messages as noticed and emit MsgsNoticed.

Some thoughts:

• This will mean that, if there are some fresh messages and then some seen messages on the server, the user will never be notified about the fresh messages. Though I can't think of a case where this would make problems.
• But, from an implementation viewpoint it seems better to tackle Send MDNs to self #7005 first. Then, the logic will be: when a self-sent MDN arrives for a message, mark all preceding (by timestamp_sort) chat messages as noticed and emit MsgsNoticed.

My preferred solution would be to get rid of the distinction between Noticed and Seen. Then, if the user opens the chat on the second device and scrolls down, all messages in the chat will be marked as seen. However, I tend to think that this would be a too big refactoring right now. The advantage would be that we simplify something, rather than complicating something.

[iequidoo]

• This will mean that, if there are some fresh messages and then some seen messages on the server, the user will never be notified about the fresh messages. Though I can't think of a case where this would make problems.

This is how it's implemented already, see Session::sync_seen_flags(), it doesn't check if there are more fresh messages in the chat before emitting MsgsNoticed. I think this is a bug, but if nobody complains, maybe let's not touch it.

• But, from an implementation viewpoint it seems better to tackle Send MDNs to self #7005 first.

EDIT: (resolved)
There's some logic already in sync_seen_flags(), if it becomes much more complex when fixing this bug, then implementing #7005 first makes sense.

[Hocuri]

Then i'd say "when a self-sent MDN arrives for a message" (w/o "outgoing"), this bug reproduces also w/o any outgoing messages.

Of course; I edited my post above to correct this.

[link2xt]

#7005 is higher priority that doing anything with \Seen flags or debugging any problems with seen status synchronization that is currently managed by the code which will change anyway.