bug#27427: 26.0.50; Native line numbers lead to display error in company-mode popup

[martin rudalics]

> I hoped the application would do that, via some new API.

We'd at least need something like a ‘TTY-check-popup-functions’ called
immediately before the display engine looks at the popups list: The
application could then check whether its popup is still relevant and
whether is should be redisplayed, possibly at a different location, with
different text.  If the application decides that nothing should be
changed and the desired matrix and the current matrix are the same for a
specific popup, the display engine would probably leave that popup in
the desired matrix alone.

>> For that purpose each popup would probably have to store the window it
>> originated from to handle scrolling of that window and any changes to
>> its buffer.
>
> That could be one way, but maybe we could use something more direct.

So far, the implementation of child and undecorated frames is complete.
Hence, for the moment I intend to proceed as follows: People who need
such frames should read the manual and try to provide a GUI solution for
their problem.  As soon as we have a few samples that work
satisfactorily on GUI systems, we can try to implement a fairly useful
workaround for TTY systems.  However, if people say they need to select
such frames or put the cursor into one of their windows, we have to
rethink how to implement a TTY solution if it's viable at all.

martin