nixos/xserver: add option to install custom xkb layouts

nixos/modules/module-list.nix

@@ -811,6 +811,7 @@
   ./services/web-servers/uwsgi.nix
   ./services/web-servers/varnish/default.nix
   ./services/web-servers/zope2.nix
+  ./services/x11/extra-layouts.nix
   ./services/x11/colord.nix
   ./services/x11/compton.nix
   ./services/x11/unclutter.nix

nixos/modules/services/x11/extra-layouts.nix

@@ -0,0 +1,165 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  layouts = config.services.xserver.extraLayouts;
+
+  layoutOpts = {
+    options = {
+      description = mkOption {
+        type = types.str;
+        description = "A short description of the layout.";
+      };
+
+      languages = mkOption {
+        type = types.listOf types.str;
+        description =
+        ''
+          A list of languages provided by the layout.
+          (Use ISO 639-2 codes, for example: "eng" for english)
+        '';
+      };
+
+      compatFile = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        description = ''
+          The path to the xkb compat file.
+          This file sets the compatibility state, used to preserve
+          compatibility with xkb-unaware programs.
+          It must contain a <literal>xkb_compat "name" { ... }</literal> block.
+        '';
+      };
+
+      geometryFile = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        description = ''
+          The path to the xkb geometry file.
+          This (completely optional) file describes the physical layout of
+          keyboard, which maybe be used by programs to depict it.
+          It must contain a <literal>xkb_geometry "name" { ... }</literal> block.
+        '';
+      };
+
+      keycodesFile = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        description = ''
+          The path to the xkb keycodes file.
+          This file specifies the range and the interpretation of the raw
+          keycodes sent by the keyboard.
+          It must contain a <literal>xkb_keycodes "name" { ... }</literal> block.
+        '';
+      };
+
+      symbolsFile = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        description = ''
+          The path to the xkb symbols file.
+          This is the most important file: it defines which symbol or action
+          maps to each key and must contain a
+          <literal>xkb_symbols "name" { ... }</literal> block.
+        '';
+      };
+
+      typesFile = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        description = ''
+          The path to the xkb types file.
+          This file specifies the key types that can be associated with
+          the various keyboard keys.
+          It must contain a <literal>xkb_types "name" { ... }</literal> block.
+        '';
+      };
+
+    };
+  };
+
+in
+
+{
+
+  ###### interface
+
+  options.services.xserver = {
+    extraLayouts = mkOption {
+      type = types.attrsOf (types.submodule layoutOpts);
+      default = {};
+      example = literalExample
+      ''
+        {
+          mine = {
+            description = "My custom xkb layout.";
+            languages = [ "eng" ];
+            symbolsFile = /path/to/my/layout;
+          };
+        }
+      '';
+      description = ''
+        Extra custom layouts that will be included in the xkb configuration.
+        Information on how to create a new layout can be found here:
+        <link xlink:href="https://www.x.org/releases/current/doc/xorg-docs/input/XKB-Enhancing.html#Defining_New_Layouts"></link>.
+        For more examples see
+        <link xlink:href="https://wiki.archlinux.org/index.php/X_KeyBoard_extension#Basic_examples"></link>
+      '';
+    };
+
+  };
+
+  ###### implementation
+
+  config = mkIf (layouts != { }) {
+
+    # We don't override xkeyboard_config directly to
+    # reduce the amount of packages to be recompiled.
+    # Only the following packages are necessary to set
+    # a custom layout anyway:
+    nixpkgs.overlays = lib.singleton (self: super: {
+
+      xkb_patched = self.xorg.xkeyboardconfig_custom {
+        layouts = config.services.xserver.extraLayouts;
+      };
+
+      xorg = super.xorg // {
+        xorgserver = super.xorg.xorgserver.overrideAttrs (old: {
+          configureFlags = old.configureFlags ++ [
+            "--with-xkb-bin-directory=${self.xorg.xkbcomp}/bin"
+            "--with-xkb-path=${self.xkb_patched}/share/X11/xkb"
+          ];
+        });
+
+        setxkbmap = super.xorg.setxkbmap.overrideAttrs (old: {
+          postInstall =
+            ''
+              mkdir -p $out/share
+              ln -sfn ${self.xkb_patched}/etc/X11 $out/share/X11
+            '';
+        });
+
+        xkbcomp = super.xorg.xkbcomp.overrideAttrs (old: {
+          configureFlags = "--with-xkb-config-root=${self.xkb_patched}/share/X11/xkb";
+        });
+
+      };
+
+      ckbcomp = super.ckbcomp.override {
+        xkeyboard_config = self.xkb_patched;
+      };
+
+      xkbvalidate = super.xkbvalidate.override {
+        libxkbcommon = self.libxkbcommon.override {
+          xkeyboard_config = self.xkb_patched;
+        };
+      };
+
+    });
+
+    services.xserver.xkbDir = "${pkgs.xkb_patched}/etc/X11/xkb";
+
+  };
+
+}

pkgs/servers/x11/xorg/overrides.nix

@@ -1,7 +1,7 @@
 { abiCompat ? null,
   stdenv, makeWrapper, fetchurl, fetchpatch, buildPackages,
   automake, autoconf, gettext, libiconv, libtool, intltool,
-  freetype, tradcpp, fontconfig, meson, ninja,
+  freetype, tradcpp, fontconfig, meson, ninja, ed,
   libGL, spice-protocol, zlib, libGLU, dbus, libunwind, libdrm,
   mesa, udev, bootstrap_cmds, bison, flex, clangStdenv, autoreconfHook,
   mcpp, epoxy, openssl, pkgconfig, llvm_6,
@@ -423,6 +423,85 @@ self: super:
     '';
   });
 
+  # xkeyboardconfig variant extensible with custom layouts.
+  # See nixos/modules/services/x11/extra-layouts.nix
+  xkeyboardconfig_custom = { layouts ? { } }:
+  let
+    patchIn = name: layout:
+    with layout;
+    with lib;
+    ''
+        # install layout files
+        ${optionalString (compatFile   != null) "cp '${compatFile}'   'compat/${name}'"}
+        ${optionalString (geometryFile != null) "cp '${geometryFile}' 'geometry/${name}'"}
+        ${optionalString (keycodesFile != null) "cp '${keycodesFile}' 'keycodes/${name}'"}
+        ${optionalString (symbolsFile  != null) "cp '${symbolsFile}'  'symbols/${name}'"}
+        ${optionalString (typesFile    != null) "cp '${typesFile}'    'types/${name}'"}
+
+        # patch makefiles
+        for type in compat geometry keycodes symbols types; do
+          if ! test -f "$type/${name}"; then
+            continue
+          fi
+          test "$type" = geometry && type_name=geom || type_name=$type
+          ${ed}/bin/ed -v $type/Makefile.am <<EOF
+        /''${type_name}_DATA =
+        a
+        ${name} \\
+        .
+        w
+        EOF
+          ${ed}/bin/ed -v $type/Makefile.in <<EOF
+        /''${type_name}_DATA =
+        a
+        ${name} \\
+        .
+        w
+        EOF
+        done
+
+        # add model description
+        ${ed}/bin/ed -v rules/base.xml <<EOF
+        /<\/modelList>
+        -
+        a
+        <model>
+          <configItem>
+            <name>${name}</name>
+            <_description>${layout.description}</_description>
+            <vendor>${layout.description}</vendor>
+          </configItem>
+        </model>
+        .
+        w
+        EOF
+
+        # add layout description
+        ${ed}/bin/ed -v rules/base.xml <<EOF
+        /<\/layoutList>
+        -
+        a
+        <layout>
+          <configItem>
+            <name>${name}</name>
+            <_shortDescription>${name}</_shortDescription>
+            <_description>${layout.description}</_description>
+            <languageList>
+              ${concatMapStrings (lang: "<iso639Id>${lang}</iso639Id>\n") layout.languages}
+            </languageList>
+          </configItem>
+          <variantList/>
+        </layout>
+        .
+        w
+        EOF
+    '';
+  in
+    self.xkeyboardconfig.overrideAttrs (old: {
+      buildInputs = old.buildInputs ++ [ automake ];
+      postPatch   = with lib; concatStrings (mapAttrsToList patchIn layouts);
+    });
+
   xload = super.xload.overrideAttrs (attrs: {
     nativeBuildInputs = attrs.nativeBuildInputs ++ [ gettext ];
   });