keyboard: make `layout` and `variant` optional

Also default these options to `null` for state version ≥ 19.09.

Fixes #811

Suggested-by: Sean Marshallsay <srm.1708@gmail.com>

doc/release-notes/rl-1909.xml

@@ -30,6 +30,14 @@
      Firefox package and defaults to <code>pkgs.firefox</code>.
     </para>
    </listitem>
+   <listitem>
+    <para>
+     The options <option>home.keyboard.layout</option> and
+     <option>home.keyboard.variant</option> now default to
+     <literal>null</literal>, which indicates that the system value should be
+     used.
+    </para>
+   </listitem>
   </itemizedlist>
  </section>
 </section>

modules/home-environment.nix

@@ -55,10 +55,18 @@ let
   keyboardSubModule = types.submodule {
     options = {
       layout = mkOption {
-        type = types.str;
-        default = "us";
+        type = with types; nullOr str;
+        default =
+          if versionAtLeast config.home.stateVersion "19.09"
+          then null
+          else "us";
+        defaultText = literalExample "null";
         description = ''
-          Keyboard layout.
+          Keyboard layout. If <literal>null</literal>, then the system
+          configuration will be used.
+          </para><para>
+          This defaults to <literal>null</literal> for state
+          version ≥ 19.09 and <literal>"us"</literal> otherwise.
         '';
       };
 
@@ -81,11 +89,19 @@ let
       };
 
       variant = mkOption {
-        type = types.str;
-        default = "";
+        type = with types; nullOr str;
+        default =
+          if versionAtLeast config.home.stateVersion "19.09"
+          then null
+          else "";
+        defaultText = literalExample "null";
         example = "colemak";
         description = ''
-          X keyboard variant.
+          X keyboard variant. If <literal>null</literal>, then the
+          system configuration will be used.
+          </para><para>
+          This defaults to <literal>null</literal> for state
+          version ≥ 19.09 and <literal>""</literal> otherwise.
         '';
       };
     };

modules/xsession.nix

@@ -104,16 +104,14 @@ in
             Type = "oneshot";
             RemainAfterExit = true;
             ExecStart =
+              with config.home.keyboard;
               let
-                args = concatStringsSep " " (
-                  [
-                    "-layout '${config.home.keyboard.layout}'"
-                    "-variant '${config.home.keyboard.variant}'"
-                  ] ++
-                  (map (v: "-option '${v}'") config.home.keyboard.options)
-                );
+                args =
+                  optional (layout != null) "-layout '${layout}'"
+                  ++ optional (variant != null) "-variant '${variant}'"
+                  ++ map (v: "-option '${v}'") options;
               in
-                "${pkgs.xorg.setxkbmap}/bin/setxkbmap ${args}";
+                "${pkgs.xorg.setxkbmap}/bin/setxkbmap ${toString args}";
           };
         };
       };

tests/modules/misc/xsession/default.nix

@@ -1,3 +1,4 @@
 {
   xsession-basic = ./basic.nix;
+  xsession-keyboard-without-layout = ./keyboard-without-layout.nix;
 }

tests/modules/misc/xsession/keyboard-without-layout-expected.service

@@ -0,0 +1,12 @@
+[Install]
+WantedBy=graphical-session.target
+
+[Service]
+ExecStart=@setxkbmap@/bin/setxkbmap -option 'ctrl:nocaps' -option 'altwin:no_win'
+RemainAfterExit=true
+Type=oneshot
+
+[Unit]
+After=graphical-session-pre.target
+Description=Set up keyboard in X
+PartOf=graphical-session.target

tests/modules/misc/xsession/keyboard-without-layout.nix

@@ -0,0 +1,33 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  config = {
+    home.stateVersion = "19.09";
+
+    home.homeDirectory = "/test-home";
+
+    home.keyboard = {
+      options = [ "ctrl:nocaps" "altwin:no_win" ];
+    };
+
+    xsession = {
+      enable = true;
+      windowManager.command = "window manager command";
+      importedVariables = [ "EXTRA_IMPORTED_VARIABLE" ];
+      initExtra = "init extra commands";
+      profileExtra = "profile extra commands";
+    };
+
+    nmt.script = ''
+      assertFileExists home-files/.config/systemd/user/setxkbmap.service
+      assertFileContent \
+        home-files/.config/systemd/user/setxkbmap.service \
+        ${pkgs.substituteAll {
+          src = ./keyboard-without-layout-expected.service;
+          inherit (pkgs.xorg) setxkbmap;
+        }}
+    '';
+  };
+}