core/pkgs/by-name/fo/fontconfig/make-fonts-cache.nix

{ runCommand, lib, fontconfig, fontDirectories }:

runCommand "fc-cache" {
  nativeBuildInputs = [ fontconfig.bin ];
  preferLocalBuild = true;
  allowSubstitutes = false;
  passAsFile = [ "fontDirs" ];
  fontDirs = ''
    <!-- Font directories -->
    ${lib.concatStringsSep "\n"
    (map (font: "<dir>${font}</dir>") fontDirectories)}
  '';
} ''
  export FONTCONFIG_FILE=$(pwd)/fonts.conf

  cat > fonts.conf << EOF
  <?xml version='1.0'?>
  <!DOCTYPE fontconfig SYSTEM 'urn:fontconfig:fonts.dtd'>
  <fontconfig>
    <include>${fontconfig.out}/etc/fonts/fonts.conf</include>
    <cachedir>$out</cachedir>
  EOF
  cat "$fontDirsPath" >> fonts.conf
  echo "</fontconfig>" >> fonts.conf

  mkdir -p $out
  fc-cache -sv

  # This is not a cache dir in the normal sense -- it won't be automatically
  # recreated.
  rm -f "$out/CACHEDIR.TAG"
''