bug#42943: 28.0.50; Emacsclient crashes in ftcrfont_glyph_extents

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: contovob@tcd.ie,  larsi@gnus.org,  42943@debbugs.gnu.org
> Date: Sat, 24 Oct 2020 15:27:39 +0200
> 
> static int
> fill_gstring_glyph_string (struct glyph_string *s, int face_id,
>                          int start, int end, int overlaps)
> {
>   struct glyph *glyph, *last;
>   Lisp_Object lgstring;
>   int i;
>   bool glyph_not_available_p;
> 
>   s->for_overlaps = overlaps;
>   glyph = s->row->glyphs[s->area] + start;
>   last = s->row->glyphs[s->area] + end;
>   glyph_not_available_p = glyph->glyph_not_available_p;
>   s->cmp_id = glyph->u.cmp.id;
>   s->cmp_from = glyph->slice.cmp.from;
>   s->cmp_to = glyph->slice.cmp.to + 1;
>   s->face = FACE_FROM_ID (s->f, face_id);
>   lgstring = composition_gstring_from_id (s->cmp_id);
>   s->font = XFONT_OBJECT (LGSTRING_FONT (lgstring)); <----
> 
> so itʼs the caching in the Lisp_Object for the composition thatʼs
> causing the problem.

OK, so when we are about to release a font, we need to go over all the
LGSTRING objects in gstring_hash_table, and remove from that cache
every LGSTRING whose LGSTRING_FONT object holds the font we are about
to release.