bug#27647: 26.0.50; Line numbers implemented natively disappear momentarily when frame out of focus

[Eli Zaretskii]

> Date: Sat, 14 Oct 2017 10:36:07 +0200
> From: martin rudalics <rudalics@gmx.at>
> CC: 27647@debbugs.gnu.org, kaushal.modi@gmail.com, 
>  jonaswestlund101@gmail.com, npostavs@users.sourceforge.net
> 
>  >> It is indeed a GTK3 build and setting x-gtk-use-system-tooltips to nil 
> does indeed make this problem go away.
>  >
>  > What about disabling scroll-bar-mode, while leaving the GTK tooltips
>  > in use -- does that also make the problem go away?
> 
> What were your thoughts here?  That clearing the scroll bar area would
> erase the line numbers?

I was trying to establish what was different from my build that caused
the numbers to disappear.  When there's a GTK scroll bar, redisplay
causes the frame's garbaged flag be set, which is something I could
try emulating here under a debugger.

Not sure what GTK tooltips have to do with this, as AFAICS displaying
a GTK tooltip shouldn't trigger redisplay.

To make line numbers disappear, some code has to trigger redisplay
with display-line-numbers somehow reset to nil.  If you can reproduce
the recipe posted by Romanos, then please try finding the code which
resets that variable, perhaps by making a different buffer current or
something.