anchor.diff:  
       # Actually build the font:
       cd font
  -    scfbuild -c scfbuild-${variant}.yml
  +    scfbuild ${scfbuildOptions} -c scfbuild-${variant}.yml
     '';
   
     installPhase = ''
  
positive.code: { stdenv
  , fetchFromGitHub
  , scfbuild
  , variant ? "color" # "color" or "black"
  }:
  
  
negative.code:     [ "color"              "black"              ]
      [ "OpenMoji-Color.ttf" "OpenMoji-Black.ttf" ]
      variant;
    scfbuildOptions = stdenv.lib.optionalString (variant == "black") "--glyph-only";
  
    # We have to use their scfbuild fork:
    # https://github.com/hfg-gmuend/openmoji/tree/master/font#setup
    scfbuildPatched = scfbuild.overrideAttrs (old: {
      src = fetchFromGitHub {
        owner = "b-g";
        repo = "scfbuild";
        rev = "880f690332fc9cc4dee0790921d331f13bd5acaa";
        sha256 = "0d61gn69hgxn17jvs69xpblq9z1l85aymbrn6jjwqamhpcl42c04";
      };
      propagatedBuildInputs = old.propagatedBuildInputs ++ [ python3Packages.lxml ];
    });
  
  in stdenv.mkDerivation rec {
    pname = "openmoji";
    version = "12.4.0";
  
    src = fetchFromGitHub {
      owner = "hfg-gmuend";
      repo = pname;
      rev = version;
      sha256 = "0zis0i7fn7dqv39c9ms7f1p4dqqzwdfwkdgrijaak1cmb8rkn3a0";
    };
  
    nativeBuildInputs = [
      scfbuildPatched
    ];
  
    # Some id and data-* attributes in the svg files contain unicode characters,
  