bug#41645: 27.0.91; Combining Grapheme Joiner (#x34f) gui artifacts

[Pip Cet <pipcet@gmail.com>]

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On Mon, Jun 1, 2020 at 3:31 PM Eli Zaretskii <eliz@gnu.org> wrote:
> > After emacs -Q, open a unicode text file and type a few letters, then
> > the Combining Grapheme Joiner (C-x 8 RET 34f), then a few more
> > letters. Press and hold the left arrow key to go back across the CGJ and
> > here it leaves behind a second box cursor while the actual cursor
> > continues to move across the text beyond. If you input multiple CGJs
> > you'll get multiple box cursors scattered wherever you put them,
> > assuming you don't change to the right arrow and hold that down, which
> > removes the artifacts as it goes along. (See attached image, with 3
> > artifacts in a line and the actual cursor off to the left.)
>
> I cannot reproduce this on my system, FWIW.  Very strange.

I can reproduce this, but it depends on which font it uses. Is it
possible it's bug 41454? I'm attaching that patch in case it does
anything and people feel like testing it.

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From c1d4778001567f7dfc7825b69193089ec69897bb Mon Sep 17 00:00:00 2001
From: Pip Cet <pipcet@gmail.com>
Date: Sun, 31 May 2020 19:55:48 +0000
Subject: [PATCH] Don't get confused by mid-gstring face changes (bug#41454)

* src/xdisp.c (fill_gstring_glyph_string): Don't extend the glyph
string past face changes.
---
 src/xdisp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/xdisp.c b/src/xdisp.c
index db0ec68315..989958fa11 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -27698,6 +27698,7 @@ fill_gstring_glyph_string (struct glyph_string *s, int face_id,
   while (glyph < last
 	 && glyph->u.cmp.automatic
 	 && glyph->u.cmp.id == s->cmp_id
+	 && glyph->face_id == face_id
 	 && s->cmp_to == glyph->slice.cmp.from)
     {
       s->width += glyph->pixel_width;
-- 
2.27.0.rc0