[gentoo-user] Remove codepoints from fonts with fontconfig

[tastytea]

Hi,
i added a colour emoji font as my last preferred font to fontconfig and
want to get all emojis from it. The problem is, that my first preferred
font contains some mono coloured emojis that override the colour emoji
font. This is my config:

  <alias>
    <family>monospace</family>
    <prefer>
      <family>Source Code Pro</family>
      <family>Source Han Mono</family>
      <family>Noto Color Emoji</family>
    </prefer>
  </alias>

and the same for serif and sans-serif[1].

I tried to “remove” the offending codepoints from all fonts matching
*Source* like this:

  <match target="scan">
    <test name="family" compare="contains">
      <string>Source</string>
    </test>
    <edit name="charset" mode="assign" binding="same">
      <minus>
        <name>charset</name>
        <charset>
          <int>0x2764</int> <!-- ❤ -->
          <int>0x1f916</int> <!-- 🤖 -->
        </charset>
      </minus>
    </edit>
  </match>

but that only works partially. After running `fc-cache -f` the emojis
are shown correctly in xfce4-terminal and GTK 2/3 programs but not in
alacritty and Qt5 programs. Firefox gets only some of them right.
Rebooting didn't help.

Is there a way to make it work everywhere?

[1] full config:
    <https://schlomp.space/tastytea/dotfiles/src/branch/main/.config/fontconfig/fonts.conf>