fontconfig.nix

/*

Configuration files are linked to /etc/fonts/conf.d/

This module generates a package containing configuration files and link it in /etc/fonts.

Fontconfig reads files in folder name / file name order, so the number prepended to the configuration file name decide the order of parsing.
Low number means high priority.

NOTE: Please take extreme care when adjusting the default settings of this module.
People care a lot, and I mean A LOT, about their font rendering, and you will be
The Person That Broke It if it changes in a way people don't like.

See prior art:
- https://github.com/NixOS/nixpkgs/pull/194594
- https://github.com/NixOS/nixpkgs/pull/222236
- https://github.com/NixOS/nixpkgs/pull/222689

And do not repeat our mistakes.

- @K900, March 2023

*/

{ config, pkgs, lib, ... }:

with lib;

let
  cfg = config.fonts.fontconfig;

  fcBool = x: "<bool>" + (boolToString x) + "</bool>";
  pkg = pkgs.fontconfig;

  # configuration file to read fontconfig cache
  # priority 0
  cacheConf  = makeCacheConf {};

  # generate the font cache setting file
  # When cross-compiling, we can’t generate the cache, so we skip the
  # <cachedir> part. fontconfig still works but is a little slower in
  # looking things up.
  makeCacheConf = { }:
    let
      makeCache = fontconfig: pkgs.makeFontsCache { inherit fontconfig; fontDirectories = config.fonts.packages; };
      cache     = makeCache pkgs.fontconfig;
      cache32   = makeCache pkgs.pkgsi686Linux.fontconfig;
    in
    pkgs.writeText "fc-00-nixos-cache.conf" ''
      <?xml version='1.0'?>
      <!DOCTYPE fontconfig SYSTEM 'urn:fontconfig:fonts.dtd'>
      <fontconfig>
        <!-- Font directories -->
        ${concatStringsSep "\n" (map (font: "<dir>${font}</dir>") config.fonts.packages)}
        ${optionalString (pkgs.stdenv.hostPlatform == pkgs.stdenv.buildPlatform) ''
        <!-- Pre-generated font caches -->
        <cachedir>${cache}</cachedir>
        ${optionalString (pkgs.stdenv.isx86_64 && cfg.cache32Bit) ''
          <cachedir>${cache32}</cachedir>
        ''}
        ''}
      </fontconfig>
    '';

  # rendering settings configuration file
  # priority 10
  renderConf = pkgs.writeText "fc-10-nixos-rendering.conf" ''
    <?xml version='1.0'?>
    <!DOCTYPE fontconfig SYSTEM 'urn:fontconfig:fonts.dtd'>
    <fontconfig>

      <!-- Default rendering settings -->
      <match target="pattern">
        <edit mode="append" name="hinting">
          ${fcBool cfg.hinting.enable}
        </edit>
        <edit mode="append" name="autohint">
          ${fcBool cfg.hinting.autohint}
        </edit>
      </match>

    </fontconfig>
  '';

  # local configuration file
  localConf = pkgs.writeText "fc-local.conf" cfg.localConf;

  # default fonts configuration file
  # priority 52
  defaultFontsConf =
    let genDefault = fonts: name:
      optionalString (fonts != []) ''
        <alias binding="same">
          <family>${name}</family>
          <prefer>
          ${concatStringsSep ""
          (map (font: ''
            <family>${font}</family>
          '') fonts)}
          </prefer>
        </alias>
      '';
    in
    pkgs.writeText "fc-52-nixos-default-fonts.conf" ''
    <?xml version='1.0'?>
    <!DOCTYPE fontconfig SYSTEM 'urn:fontconfig:fonts.dtd'>
    <fontconfig>

      <!-- Default fonts -->
      ${genDefault cfg.defaultFonts.sansSerif "sans-serif"}

      ${genDefault cfg.defaultFonts.serif     "serif"}

      ${genDefault cfg.defaultFonts.monospace "monospace"}

      ${genDefault cfg.defaultFonts.emoji "emoji"}

    </fontconfig>
  '';

  # bitmap font options
  # priority 53
  rejectBitmaps = pkgs.writeText "fc-53-no-bitmaps.conf" ''
    <?xml version="1.0"?>
    <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">
    <fontconfig>

    ${optionalString (!cfg.allowBitmaps) ''
    <!-- Reject bitmap fonts -->
    <selectfont>
      <rejectfont>
        <pattern>
          <patelt name="scalable"><bool>false</bool></patelt>
        </pattern>
      </rejectfont>
    </selectfont>
    ''}

    <!-- Use embedded bitmaps in fonts like Calibri? -->
    <match target="font">
      <edit name="embeddedbitmap" mode="assign">
        ${fcBool cfg.useEmbeddedBitmaps}
      </edit>
    </match>

    </fontconfig>
  '';

  # reject Type 1 fonts
  # priority 53
  rejectType1 = pkgs.writeText "fc-53-nixos-reject-type1.conf" ''
    <?xml version="1.0"?>
    <!DOCTYPE fontconfig SYSTEM "urn:fontconfig:fonts.dtd">
    <fontconfig>

    <!-- Reject Type 1 fonts -->
    <selectfont>
      <rejectfont>
        <pattern>
          <patelt name="fontformat"><string>Type 1</string></patelt>
        </pattern>
      </rejectfont>
    </selectfont>

    </fontconfig>
  '';

  # Replace default linked config with a different variant
  replaceDefaultConfig = defaultConfig: newConfig: ''
    rm $dst/${defaultConfig}
    ln -s ${pkg.out}/share/fontconfig/conf.avail/${newConfig} \
          $dst/
  '';

  # fontconfig configuration package
  confPkg = pkgs.runCommand "fontconfig-conf" {
    preferLocalBuild = true;
  } ''
    dst=$out/etc/fonts/conf.d
    mkdir -p $dst

    # fonts.conf
    ln -s ${pkg.out}/etc/fonts/fonts.conf \
          $dst/../fonts.conf
    # TODO: remove this legacy symlink once people stop using packages built before #95358 was merged
    mkdir -p $out/etc/fonts/2.11
    ln -s /etc/fonts/fonts.conf \
          $out/etc/fonts/2.11/fonts.conf

    # fontconfig default config files
    ln -s ${pkg.out}/etc/fonts/conf.d/*.conf \
          $dst/

    ${optionalString (!cfg.antialias)
      (replaceDefaultConfig "10-yes-antialias.conf"
        "10-no-antialias.conf")
    }

    ${optionalString (cfg.hinting.style != "slight")
      (replaceDefaultConfig "10-hinting-slight.conf"
        "10-hinting-${cfg.hinting.style}.conf")
    }

    ${optionalString (cfg.subpixel.rgba != "none")
      (replaceDefaultConfig "10-sub-pixel-none.conf"
        "10-sub-pixel-${cfg.subpixel.rgba}.conf")
    }

    ${optionalString (cfg.subpixel.lcdfilter != "default")
      (replaceDefaultConfig "11-lcdfilter-default.conf"
        "11-lcdfilter-${cfg.subpixel.lcdfilter}.conf")
    }

    # 00-nixos-cache.conf
    ln -s ${cacheConf}  $dst/00-nixos-cache.conf

    # 10-nixos-rendering.conf
    ln -s ${renderConf}       $dst/10-nixos-rendering.conf

    # 50-user.conf
    ${optionalString (!cfg.includeUserConf) ''
    rm $dst/50-user.conf
    ''}

    # local.conf (indirect priority 51)
    ${optionalString (cfg.localConf != "") ''
    ln -s ${localConf}        $dst/../local.conf
    ''}

    # 52-nixos-default-fonts.conf
    ln -s ${defaultFontsConf} $dst/52-nixos-default-fonts.conf

    # 53-no-bitmaps.conf
    ln -s ${rejectBitmaps} $dst/53-no-bitmaps.conf

    ${optionalString (!cfg.allowType1) ''
    # 53-nixos-reject-type1.conf
    ln -s ${rejectType1} $dst/53-nixos-reject-type1.conf
    ''}
  '';

  # Package with configuration files
  # this merge all the packages in the fonts.fontconfig.confPackages list
  fontconfigEtc = pkgs.buildEnv {
    name  = "fontconfig-etc";
    paths = cfg.confPackages;
    ignoreCollisions = true;
  };

  fontconfigNote = "Consider manually configuring fonts.fontconfig according to personal preference.";
in
{
  imports = [
    (mkRenamedOptionModule [ "fonts" "fontconfig" "ultimate" "allowBitmaps" ] [ "fonts" "fontconfig" "allowBitmaps" ])
    (mkRenamedOptionModule [ "fonts" "fontconfig" "ultimate" "allowType1" ] [ "fonts" "fontconfig" "allowType1" ])
    (mkRenamedOptionModule [ "fonts" "fontconfig" "ultimate" "useEmbeddedBitmaps" ] [ "fonts" "fontconfig" "useEmbeddedBitmaps" ])
    (mkRenamedOptionModule [ "fonts" "fontconfig" "ultimate" "forceAutohint" ] [ "fonts" "fontconfig" "forceAutohint" ])
    (mkRenamedOptionModule [ "fonts" "fontconfig" "ultimate" "renderMonoTTFAsBitmap" ] [ "fonts" "fontconfig" "renderMonoTTFAsBitmap" ])
    (mkRemovedOptionModule [ "fonts" "fontconfig" "forceAutohint" ] "")
    (mkRemovedOptionModule [ "fonts" "fontconfig" "renderMonoTTFAsBitmap" ] "")
    (mkRemovedOptionModule [ "fonts" "fontconfig" "dpi" ] "Use display server-specific options")
    (mkRemovedOptionModule [ "hardware" "video" "hidpi" "enable" ] fontconfigNote)
    (mkRemovedOptionModule [ "fonts" "optimizeForVeryHighDPI" ] fontconfigNote)
  ] ++ lib.forEach [ "enable" "substitutions" "preset" ]
     (opt: lib.mkRemovedOptionModule [ "fonts" "fontconfig" "ultimate" "${opt}" ] ''
       The fonts.fontconfig.ultimate module and configuration is obsolete.
       The repository has since been archived and activity has ceased.
       https://github.com/bohoomil/fontconfig-ultimate/issues/171.
       No action should be needed for font configuration, as the fonts.fontconfig
       module is already used by default.
     '');

  options = {

    fonts = {

      fontconfig = {
        enable = mkOption {
          type = types.bool;
          default = true;
          description = lib.mdDoc ''
            If enabled, a Fontconfig configuration file will be built
            pointing to a set of default fonts.  If you don't care about
            running X11 applications or any other program that uses
            Fontconfig, you can turn this option off and prevent a
            dependency on all those fonts.
          '';
        };

        confPackages = mkOption {
          internal = true;
          type     = with types; listOf path;
          default  = [ ];
          description = lib.mdDoc ''
            Fontconfig configuration packages.
          '';
        };

        antialias = mkOption {
          type = types.bool;
          default = true;
          description = lib.mdDoc ''
            Enable font antialiasing. At high resolution (> 200 DPI),
            antialiasing has no visible effect; users of such displays may want
            to disable this option.
          '';
        };

        localConf = mkOption {
          type = types.lines;
          default = "";
          description = lib.mdDoc ''
            System-wide customization file contents, has higher priority than
            `defaultFonts` settings.
          '';
        };

        defaultFonts = {
          monospace = mkOption {
            type = types.listOf types.str;
            default = ["DejaVu Sans Mono"];
            description = lib.mdDoc ''
              System-wide default monospace font(s). Multiple fonts may be
              listed in case multiple languages must be supported.
            '';
          };

          sansSerif = mkOption {
            type = types.listOf types.str;
            default = ["DejaVu Sans"];
            description = lib.mdDoc ''
              System-wide default sans serif font(s). Multiple fonts may be
              listed in case multiple languages must be supported.
            '';
          };

          serif = mkOption {
            type = types.listOf types.str;
            default = ["DejaVu Serif"];
            description = lib.mdDoc ''
              System-wide default serif font(s). Multiple fonts may be listed
              in case multiple languages must be supported.
            '';
          };

          emoji = mkOption {
            type = types.listOf types.str;
            default = ["Noto Color Emoji"];
            description = lib.mdDoc ''
              System-wide default emoji font(s). Multiple fonts may be listed
              in case a font does not support all emoji.

              Note that fontconfig matches color emoji fonts preferentially,
              so if you want to use a black and white font while having
              a color font installed (eg. Noto Color Emoji installed alongside
              Noto Emoji), fontconfig will still choose the color font even
              when it is later in the list.
            '';
          };
        };

        hinting = {
          enable = mkOption {
            type = types.bool;
            default = true;
            description = lib.mdDoc ''
              Enable font hinting. Hinting aligns glyphs to pixel boundaries to
              improve rendering sharpness at low resolution. At high resolution
              (> 200 dpi) hinting will do nothing (at best); users of such
              displays may want to disable this option.
            '';
          };

          autohint = mkOption {
            type = types.bool;
            default = false;
            description = lib.mdDoc ''
              Enable the autohinter in place of the default interpreter.
              The results are usually lower quality than correctly-hinted
              fonts, but better than unhinted fonts.
            '';
          };

          style = mkOption {
            type = types.enum ["none" "slight" "medium" "full"];
            default = "slight";
            description = lib.mdDoc ''
              Hintstyle is the amount of font reshaping done to line up
              to the grid.

              slight will make the font more fuzzy to line up to the grid but
              will be better in retaining font shape, while full will be a
              crisp font that aligns well to the pixel grid but will lose a
              greater amount of font shape.
            '';
            apply =
              val:
              let
                from = "fonts.fontconfig.hinting.style";
                val' = lib.removePrefix "hint" val;
                warning = "The option `${from}` contains a deprecated value `${val}`. Use `${val'}` instead.";
              in
              lib.warnIf (lib.hasPrefix "hint" val) warning val';
          };
        };

        includeUserConf = mkOption {
          type = types.bool;
          default = true;
          description = lib.mdDoc ''
            Include the user configuration from
            {file}`~/.config/fontconfig/fonts.conf` or
            {file}`~/.config/fontconfig/conf.d`.
          '';
        };

        subpixel = {

          rgba = mkOption {
            default = "none";
            type = types.enum ["rgb" "bgr" "vrgb" "vbgr" "none"];
            description = lib.mdDoc ''
              Subpixel order. The overwhelming majority of displays are
              `rgb` in their normal orientation. Select
              `vrgb` for mounting such a display 90 degrees
              clockwise from its normal orientation or `vbgr`
              for mounting 90 degrees counter-clockwise. Select
              `bgr` in the unlikely event of mounting 180
              degrees from the normal orientation. Reverse these directions in
              the improbable event that the display's native subpixel order is
              `bgr`.
            '';
          };

          lcdfilter = mkOption {
            default = "default";
            type = types.enum ["none" "default" "light" "legacy"];
            description = lib.mdDoc ''
              FreeType LCD filter. At high resolution (> 200 DPI), LCD filtering
              has no visible effect; users of such displays may want to select
              `none`.
            '';
          };

        };

        cache32Bit = mkOption {
          default = false;
          type = types.bool;
          description = lib.mdDoc ''
            Generate system fonts cache for 32-bit applications.
          '';
        };

        allowBitmaps = mkOption {
          type = types.bool;
          default = true;
          description = lib.mdDoc ''
            Allow bitmap fonts. Set to `false` to ban all
            bitmap fonts.
          '';
        };

        allowType1 = mkOption {
          type = types.bool;
          default = false;
          description = lib.mdDoc ''
            Allow Type-1 fonts. Default is `false` because of
            poor rendering.
          '';
        };

        useEmbeddedBitmaps = mkOption {
          type = types.bool;
          default = false;
          description = lib.mdDoc "Use embedded bitmaps in fonts like Calibri.";
        };

      };

    };

  };
  config = mkMerge [
    (mkIf cfg.enable {
      environment.systemPackages    = [ pkgs.fontconfig ];
      environment.etc.fonts.source  = "${fontconfigEtc}/etc/fonts/";
      security.apparmor.includes."abstractions/fonts" = ''
        # fonts.conf
        r ${pkg.out}/etc/fonts/fonts.conf,

        # fontconfig default config files
        r ${pkg.out}/etc/fonts/conf.d/*.conf,

        # 00-nixos-cache.conf
        r ${cacheConf},

        # 10-nixos-rendering.conf
        r ${renderConf},

        # 50-user.conf
        ${optionalString cfg.includeUserConf ''
        r ${pkg.out}/etc/fonts/conf.d.bak/50-user.conf,
        ''}

        # local.conf (indirect priority 51)
        ${optionalString (cfg.localConf != "") ''
        r ${localConf},
        ''}

        # 52-nixos-default-fonts.conf
        r ${defaultFontsConf},

        # 53-no-bitmaps.conf
        r ${rejectBitmaps},

        ${optionalString (!cfg.allowType1) ''
        # 53-nixos-reject-type1.conf
        r ${rejectType1},
        ''}
      '';
    })
    (mkIf cfg.enable {
      fonts.fontconfig.confPackages = [ confPkg ];
    })
  ];

}