bug#39799: 28.0.50; Most emoji sequences don’t render correctly

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: 39799@debbugs.gnu.org,  mfabian@redhat.com
> Date: Fri, 28 Feb 2020 17:24:58 +0100
> 
> Most of the emojis in emoji-sequences.txt can be made to use Noto
> Color Emoji, but some canʼt. e.g.
> 
> #x24c2 Ⓜ
> 
> is stubbornly not being displayed using Noto Color Emoji, even though
> that font has a glyph for it, and Iʼve added:
> 
>      (set-fontset-font "fontset-default" symbol-subgroup
>                       '("Noto Color Emoji" . "iso10646-1") nil
>                       'prepend)
> 
> just after the similar setting for Symbola in
> lisp/international/fontset.el
> 
> Itʼs not being displayed with the default font, and setting
> use-default-font-for-symbols to nil makes no difference. Itʼs using:
> 
>     ftcrhb:-GOOG-Noto Sans CJK 
> JP-normal-normal-normal-*-16-*-*-*-*-0-iso10646-1 (#x3F8)
> 
> However, if I
> eval
> 
>      (set-fontset-font nil #x24c2
>                       '("Noto Color Emoji" . "iso10646-1") nil
>                       'prepend)
> 
> in the frame displaying the character, then it does use Noto Color
> Emoji. What am I missing?

Which part makes the difference: the "fontset-default" vs nil or
symbol-subgroup vs an explicit codepoint?