Fixes#16284.
Most of the work for this was done when we implemented correct
behavior for guest users, since they treat public streams like private
streams anyway.
The general method involves moving the messages to the new stream with
special care of UserMessage.
We delete UserMessages for subs who are losing access to the message.
For private streams with protected history, we also create UserMessage
elements for users who are not present in the old stream, since that's
important for those users to access the moved messages.
* This feature is currently only visible to admins.
* Locally echoed messages are also updated.
* Add UI for editing stream if user is admin.
* Show propagate mode selector if either stream or topic changed.
This completes the implementation of support for moving a topic to
another stream by adding a basic UI for it.
Fixes#6427, which was previously the most-upvoted issue request in
Zulip.
There are likely to be a bunch of follow-up UI improvements on top of
this change to fully flesh out the feature.
Aman Agrawal
Tim Abbott
Aman Agrawal
Tim Abbott
Rishi Gupta