numlock: add module

This adds an option `xsession.numlock` that enable the Num Lock key
when starting a graphical session.

Fixes #651

modules/misc/numlock.nix

@@ -0,0 +1,34 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+
+  cfg = config.xsession.numlock;
+
+in
+
+{
+  options = {
+    xsession.numlock.enable = mkEnableOption "Num Lock";
+  };
+
+  config = mkIf cfg.enable {
+    systemd.user.services.numlockx = {
+      Unit = {
+        Description = "NumLockX";
+        After = [ "graphical-session-pre.target" ];
+        PartOf = [ "graphical-session.target" ];
+      };
+
+      Service = {
+        Type = "oneshot";
+        ExecStart = "${pkgs.numlockx}/bin/numlockx";
+      };
+
+      Install = {
+        WantedBy = [ "graphical-session.target" ];
+      };
+    };
+  };
+}

modules/modules.nix

@@ -28,6 +28,7 @@ let
     (loadModule ./misc/lib.nix { })
     (loadModule ./misc/news.nix { })
     (loadModule ./misc/nixpkgs.nix { })
+    (loadModule ./misc/numlock.nix { condition = hostPlatform.isLinux; })
     (loadModule ./misc/pam.nix { })
     (loadModule ./misc/qt.nix { })
     (loadModule ./misc/submodule-support.nix { })