xmonad: add module

modules/default.nix

@@ -53,6 +53,7 @@ let
     ./systemd.nix
     ./xresources.nix
     ./xsession.nix
+    ./xmonad.nix
     <nixpkgs/nixos/modules/misc/assertions.nix>
     <nixpkgs/nixos/modules/misc/meta.nix>
   ];

modules/xmonad.nix

@@ -0,0 +1,107 @@
+{ config, pkgs, lib, ... }:
+
+with lib;
+with import ./lib/dag.nix { inherit lib; };
+
+let
+  cfg = config.xmonad;
+  homefile = ".xmonad/xmonad.hs";
+  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";
+    haskellPackages = mkOption {
+      default = pkgs.haskellPackages;
+      defaultText = "pkgs.haskellPackages";
+      example = literalExample "pkgs.haskell.packages.ghc784";
+      description = ''
+        haskellPackages 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 attrset 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;
+      example = literalExample ''
+        pkgs.writeText "xmonad.hs" '''
+          import XMonad
+          main = xmonad def
+              { terminal    = "urxvt"
+              , modMask     = mod4Mask
+              , borderWidth = 3
+              }
+        '''
+      '';
+      description = ''
+        The config to be used for Xmonad. This must be an absolute path or null,
+        in which case ~/.xmonad/xmonad.hs doesn't get managed by HM.
+
+        Some options are:
+
+        - Directly import a file with <literal>config = ./xmonad.hs;</literal>.
+        - Use <literal>pkgs.writeText "xmonad" '''&lt;config&gt;'''</literal>.
+        - Substitute @val@'s in a file with direct store binaries with
+        the substitute bash function.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable (mkMerge [
+    {
+      xsession.windowManager = mkDefault "${xmonad}/bin/xmonad";
+
+      home.packages = [ xmonad ];
+    }
+    (mkIf (cfg.config != null) {
+
+      home.file.${homefile}.source = cfg.config;
+
+      home.activation.checkXMonad = dagEntryBefore [ "linkGeneration" ] ''
+        if ! cmp ${cfg.config} $HOME/${homefile} >/dev/null; then
+          _XMONAD_CHANGED=1
+        else
+          _XMONAD_CHANGED=0
+        fi
+      '';
+
+      home.activation.applyXMonad = dagEntryAfter [ "linkGeneration" ] ''
+        if [ $_XMONAD_CHANGED = 1 ]; then
+          echo Recompiling Xmonad
+          ${xmonad}/bin/xmonad --recompile
+          echo Restarting Xmonad
+          ${xmonad}/bin/xmonad --restart
+        fi
+      '';
+    })
+  ]);
+}