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

[Eli Zaretskii <eliz@gnu.org>]

> Date: Sun, 25 Jun 2017 19:10:01 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: alexanderm@web.de, 27427@debbugs.gnu.org
> 
>  > I'd rather think in terms of "submargins", one per "category", and
>  > having an alist of particular properties of each of those categories.
> 
> Once we do that we should try to accommodate as much as possible in the
> concept we provide and I think that having ‘follow-mode’ implemented by
> the display engine would be quite valuable.  So I would vote for a more
> general solution that encompasses it as well.

I think people who lobby for more extensive and flexible use of the
margins underestimate the amount of work something like that will
take.  The current management of the margin display is exceedingly
rudimentary.  Most of the sophisticated layout stuff we have in the
text area -- truncation and continuation markers, word-wrap, etc. --
all that doesn't exist there.  And the cursor cannot enter the
margins.  Basically, we just put there glyphs until the available
space is exhausted, and that's it.

By contrast, you guys are dreaming about full-fledged additional "text
areas" with all the features we now support in the single one we have.
That's an entirely new ballpark game, although I agree that it's a
natural generalization and extension of what we have.  The problem is
that the knowledge of the basic canvas geometry is hard-coded in many
places in the display code, and all of them will have to be reworked.

I think this would be a very good project and a significant progress
for Emacs, so I'd welcome such a development.  Just don't
underestimate the magnitude of the task.