bug#50660: 28.0.50; Text artifacting when the cursor moves over text under mouse face that originally displayed a box

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: larsi@gnus.org,  50660@debbugs.gnu.org
> Date: Thu, 14 Oct 2021 18:52:48 +0800
> 
> I don't know how to apply the fixes to xterm.c to the other window
> systems, so someone who can needs to apply them to the NS and MS-Windows
> ports.

You just make the same changes there, and ask people with access to
those other systems to test it.  But see below.

> @@ -1799,11 +1799,24 @@ x_draw_glyph_string_foreground (struct glyph_string 
> *s)
>  {
>    int i, x;
>  
> +  struct face *face_for_box_line = s->face;
> +
> +  if (s->hl == DRAW_CURSOR && cursor_in_mouse_face_p (s->w))
> +    {
> +      /* In this situation, the cursor is in the mouse face, but
> +      s->face hasn't been updated with the mouse face yet. */
> +      face_for_box_line =
> +     FACE_FROM_ID_OR_NULL (s->f, MOUSE_HL_INFO (s->f)->mouse_face_face_id);
> +
> +      if (!face_for_box_line)
> +     face_for_box_line = FACE_FROM_ID (s->f, MOUSE_FACE_ID);
> +    }

Can't we "fix" this face in xdisp.c, before calling the
terminal-specific backend?  The bonus will be that we then do it only
in one place.