bug#75291: Redisplay not updating fringe when face filter changes

[Daniel Colascione <dancol@dancol.org>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Daniel Colascione <dancol@dancol.org>
>> Cc: 75291@debbugs.gnu.org,  mina86@mina86.com
>> Date: Fri, 03 Jan 2025 12:25:05 -0500
>> 
>> > I think it depends on whether you use double-buffering (some people
>> > don't or cannot) and whether you have the mouse pointer over an Emacs
>> > frame.  Also, depending on the GUI toolkit, the decorations might
>> > flicker.
>> 
>> TTY windows don't have fringes, and the most commonly-used window
>> systems all do atomic updates nowadays.
>
> People still report flickering from time to time, so I don't think
> this never happens.
>
>> > So you want to add to display_line code that sets each glyph_row's
>> > redraw_fringe_bitmaps_p flag when the fringe face changes?  That could
>> > probably work, provided that we disable redisplay optimizations which
>> > might avoid calling display_line (you will see that we already disable
>> > such optimizations when overlay_arrows_changed_p returns non-zero).
>> > We might actually need to disable more of the optimizations, because
>> > the overlay-arrow thing doesn't contradict the optimizations that
>> > scroll the pixels, something that reaction to changes in the fringe
>> > face cannot tolerate.
>> 
>> That might work, but I don't think we even need anything that
>> complicated or low-level.  Not many are using :filtered now, and those
>> that do big redraws anyway.  How about this simpler code that gets us
>> correctness, albeit more conservatively?
>
> Doesn't that only support face remapping with :filtered attribute?
> What about the more general case where the fringe face is remapped in
> a way that's independent of the windows?

That seems to work already. It's only in the fringe that I see problems
--- it just doesn't seem worth it to limit the redraw to the fringe.