Subject: bug#54970: 28.1; Some emoji no longer display

From: Howard Melman <[email-masked]>
Date: Fri, 22 Apr 2022 17:56:34 -0400

I have two follow up questions.

First, is composition supposed to work everywhere?  I have the following
code to add to the C-x 8 map and I use which-key from gnu elpa but its
displayed help isn't composing.  It's just a buffer named " *which-key*"
and I can switch to it but can't do anything in it to inspect things.  It's hard
to follow how they're writing to it.  I can open a which-key bug but I wanted
to understand more about composing and if it's supposed to be enabled
everywhere (which-key doesn't reference it at all)

Second, I'm using this now for emoji fonts:

(set-fontset-font t 'symbol '("Apple Color Emoji" . "iso10646-1") nil 'prepend)

I saw from a related reddit post that the font Symbola has some other glyphs
that seemed of interest.  It renders things as plain graphics not as color
emoji which is fine (or preferred) for math symbols.  I'd like to use Apple
Color Emoji first and then if it doesn't support a character fall back on
Symbola.  I thought to do that with:

(set-fontset-font t 'symbol '("Symbola" . "iso10646-1") nil 'prepend)
(set-fontset-font t 'symbol '("Apple Color Emoji" . "iso10646-1") nil 'prepend)

But it didn't work.  Most emoji were rending as Symbola.  I then removed the
first line and restarted emacs (so just my original line is in the init) and emoji
were *still* rendered with Symbola.  It wasn't until I disabled the font in the
mac utility Font Book.app that it went back to full color emoji rendering. I recall
a similar issue a year ago trying to get Julia Mono working too.

What's the right incantation to do this?  I tried with just the 'emoji script on the 
second call but it didn't help. How and when is emacs searching
for fonts to use and how does it relate to the above set-fontset-font calls? It's
nice that emacs just finds fonts, but it's unnerving that merely installing a font
can break what emacs displays.

Howard