bug#74337: 29.4; Visiting a file with Unicode emojis is very slow

[Eli Zaretskii <eliz@gnu.org>]

> From: Duncan Bayne <duncan@bayne.id.au>
> Cc: 74337@debbugs.gnu.org
> Date: Thu, 14 Nov 2024 22:42:29 +1100
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > OK, so how many fonts do you have installed overall on that system?
> > What do the following expressions yield when evaluated with "M-:"?
> >
> >   (length (font-family-list))
> >   (length (x-list-fonts "*" 'default))
> 
> (length (font-family-list)) returns 10775.
> (length (x-list-fonts "*" 'default)) returns 7333.

Whoa! it's a small surprise you need to wait for so long when some
character has no font.  Why do you have so many fonts installed? do
you really need them?

> > If you install Noto Color Emoji, Emacs should use that font by default
> > for displaying emoji.
> 
> I have installed Noto from packages with:
> 
> pkg install -y \
>     noto \
>     noto-emoji \
> 
> ... and refreshed my font cache with:
> 
> fc-cache -fv
> 
> I've attached the log from fc-cache.
> 
> With this all done, most of the emoji in the file are rendered properly,
> but a few still appear as tofu, and it still takes minutes to open.

Those characters that show as tofu are not emoji.  I suggest to
install Symbola, it should have them displayed correctly.