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

[Eli Zaretskii <eliz@gnu.org>]

> From: Daniel Colascione <dancol@dancol.org>
> Cc: 75291@debbugs.gnu.org,  mina86@mina86.com
> Date: Fri, 03 Jan 2025 14:46:20 -0500
> 
> 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.

Sorry, I don't understand.  I _was_ talking about the fringe face.

But if redraw_frame solves the issue, and doesn't cause unpleasant or
expensive redraws, feel free to install on the master branch.  But
please change this:

+  if (SYMBOLP (parameter) &&
+      WINDOW_LIVE_P (window) &&
+      FRAME_WINDOW_P (WINDOW_XFRAME (w)) &&
+      !NILP (Fget (parameter, Qface_filter)) && <<<<<<<<<<<<<<<<<
+      !EQ (CDR_SAFE (old_alist_elt), value))
+    redraw_frame (WINDOW_XFRAME (w));

to say this instead:

+  if (SYMBOLP (parameter) &&
+      WINDOW_LIVE_P (window) &&
+      FRAME_WINDOW_P (WINDOW_XFRAME (w)) &&
+      EQ (Fget (parameter, Qface_filter), Qt) && <<<<<<<<<<<<<<<<<
+      !EQ (CDR_SAFE (old_alist_elt), value))
+    redraw_frame (WINDOW_XFRAME (w));

(A stylistic comment: our conventions is to put the && operator at the
beginning of a line, not at the end of a line.)