bug#40733: 28.0.50; Emacs locks up on paste (yank) of unicode characters

[Eli Zaretskii <eliz@gnu.org>]

> From: Pip Cet <pipcet@gmail.com>
> Date: Mon, 1 Jun 2020 11:44:10 +0000
> Cc: Eli Zaretskii <eliz@gnu.org>, "Basil L. Contovounesios" <contovob@tcd.ie>, Robert Pluim <rpluim@gmail.com>, 
> 	40733@debbugs.gnu.org, James Cloos <cloos@jhcloos.com>
> 
> On Mon, Jun 1, 2020 at 11:20 AM Will Bush <will.g.bush@gmail.com> wrote:
> > git clone https://github.com/adobe-fonts/adobe-blank.git
> > cd adobe-blank
> > sudo cp AdobeBlank.ttf /usr/share/fonts/
> > fc-cache
> > time emacs -Q --eval '(message "︵")' -kill
> >
> > And it took 4 minutes in the virtual machine!
> > Please try it and see if you can repro!
> 
> It's taking a while here (pretty standard GNU/Linux x86_64 system),
> but something on the order of 20 seconds, not 4 minutes.
> 
> in ftcrfont.c:
> 
>   pat = ftfont_entity_pattern (entity, pixel_size);
>   FcConfigSubstitute (NULL, pat, FcMatchPattern);
>   FcDefaultSubstitute (pat);
>   match = FcFontMatch (NULL, pat, &result); <===========
>   ftfont_fix_match (pat, match);
> 
> This is where it spends so much time. "perf record emacs -Q" suggests
> it's a function called FcCharSetSubtractCount. (You might try running
> that on your setup, too).

Thanks.

From what I see in the net search, this is a very large font, created
for some very special circumstances.  Not sure we should spend time on
this issue.  Maybe submit a bug report to Fontconfig folks.