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

[Pip Cet]

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).