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

[Eli Zaretskii]

> Cc: 27427@debbugs.gnu.org, alexanderm@web.de
> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Mon, 3 Jul 2017 03:22:56 +0300
> 
> On 7/2/17 6:18 PM, Eli Zaretskii wrote:
> 
> > We could have a feature whereby the coordinates are determined by a
> > specific buffer position shown in a "normal" window.
> 
> That's what I was thinking of as well. But that, in turn, might call for 
> some extra features:
> 
> When there is not enough space below the current line to show the popup, 
> we display it above the current line. I'd expect the new popup code 
> reposition it like that automatically as well.
> 
> But: in company we have feature where, when the popup is displayed above 
> the current line, the popup lines are inverted vertically (so that the 
> first completion is the closest to the current line visually). I'm not a 
> fan, but it's fairly popular.
> 
> If the core popup handles repositioning, it would have to handle 
> inverting (optionally) as well, or run some sort of hook to require the 
> popup items to be recomputed.

These are all doable, and AFAIU are needed even if the coordinates are
specified by the application.