xmonad: add module

Adapted from #78 and originally authored by Infinisil.

modules/misc/news.nix

@@ -288,6 +288,13 @@ in
           to your Home Manager configuration.
         '';
       }
+
+      {
+        time = "2017-10-04T18:36:07+00:00";
+        message = ''
+          A new module is available: 'xsession.windowManager.xmonad'.
+        '';
+      }
     ];
   };
 }

modules/services/window-managers/xmonad.nix

@@ -0,0 +1,86 @@
+{ pkgs }: { config, lib, ... }:
+
+with lib;
+
+let
+
+  cfg = config.xmonad;
+
+  xmonad = pkgs.xmonad-with-packages.override {
+    ghcWithPackages = cfg.haskellPackages.ghcWithPackages;
+    packages = self:
+      cfg.extraPackages self
+      ++ optionals cfg.enableContribAndExtras [
+        self.xmonad-contrib self.xmonad-extras
+      ];
+  };
+
+in
+
+{
+  options = {
+    xmonad = {
+      enable = mkEnableOption "xmonad window manager";
+
+      haskellPackages = mkOption {
+        default = pkgs.haskellPackages;
+        defaultText = "pkgs.haskellPackages";
+        example = literalExample "pkgs.haskell.packages.ghc784";
+        description = ''
+          The <varname>haskellPackages</varname> used to build xmonad
+          and other packages. This can be used to change the GHC
+          version used to build xmonad and the packages listed in
+          <varname>extraPackages</varname>.
+        '';
+      };
+
+      extraPackages = mkOption {
+        default = self: [];
+        defaultText = "self: []";
+        example = literalExample ''
+          haskellPackages: [
+            haskellPackages.xmonad-contrib
+            haskellPackages.monad-logger
+          ]
+        '';
+        description = ''
+          Extra packages available to GHC when rebuilding xmonad. The
+          value must be a function which receives the attribute set
+          defined in <varname>haskellPackages</varname> as the sole
+          argument.
+        '';
+      };
+
+      enableContribAndExtras = mkOption {
+        default = false;
+        type = types.bool;
+        description = "Enable xmonad-{contrib,extras} in xmonad.";
+      };
+
+      config = mkOption {
+        type = types.nullOr types.path;
+        default = null;
+        example = literalExample ''
+          pkgs.writeText "xmonad.hs" '''
+            import XMonad
+            main = xmonad defaultConfig
+                { terminal    = "urxvt"
+                , modMask     = mod4Mask
+                , borderWidth = 3
+                }
+          '''
+        '';
+        description = ''
+          The configuration file to be used for xmonad. This must be
+          an absolute path or <literal>null</literal> in which case
+          <filename>~/.xmonad/xmonad.hs</filename> will not be managed
+          by Home Manager.
+        '';
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    command = "${xmonad}/bin/xmonad";
+  };
+}

modules/xsession.nix

@@ -1,6 +1,7 @@
 { config, lib, pkgs, ... }:
 
 with lib;
+with import ./lib/dag.nix { inherit lib; };
 
 let
 
@@ -32,6 +33,10 @@ let
     };
   };
 
+  xmonadModule = import ./services/window-managers/xmonad.nix {
+    inherit pkgs;
+  };
+
 in
 
 {
@@ -46,7 +51,7 @@ in
           types.coercedTo
             types.str
             (command: { inherit command; usesDeprecated = true; })
-            (types.submodule wmBaseModule);
+            (types.submodule [ wmBaseModule xmonadModule ]);
         description = ''
           Window manager start command. DEPRECATED: Use
           <varname>xsession.windowManager.command</varname> instead.
@@ -69,6 +74,34 @@ in
       ];
     })
 
+    # Hack to support xsession.windowManager as a string. Once that is
+    # removed this code should go back into the xmonad.nix file.
+    (mkIf (cfg.windowManager.xmonad.enable
+        && cfg.windowManager.xmonad.config != null) {
+      home.file.".xmonad/xmonad.hs".source = cfg.windowManager.xmonad.config;
+
+      home.activation.checkXmonad = dagEntryBefore [ "linkGeneration" ] ''
+        if ! cmp --quiet \
+            "${cfg.windowManager.xmonad.config}" \
+            "$HOME/.xmonad/xmonad.hs"; then
+          xmonadChanged=1
+        fi
+      '';
+
+      home.activation.applyXmonad = dagEntryAfter [ "linkGeneration" ] ''
+        if [[ -v xmonadChanged ]]; then
+          echo "Recompiling xmonad"
+          ${cfg.windowManager.command} --recompile
+
+          # Attempt to restart xmonad if X is running.
+          if [[ -v DISPLAY ]] ; then
+            echo "Restarting xmonad"
+            ${cfg.windowManager.command} --restart
+          fi
+        fi
+      '';
+    })
+
     {
       systemd.user.services.setxkbmap = {
         Unit = {