windowManager.xmonad: Make it configurable and extensible.

nixos/modules/services/x11/window-managers/xmonad.nix

@@ -1,10 +1,14 @@
 {pkgs, config, ...}:
 
 let
-  inherit (pkgs.lib) mkOption mkIf;
+  inherit (pkgs.lib) mkOption mkIf optionals literalExample;
   cfg = config.services.xserver.windowManager.xmonad;
+  xmonadEnv = cfg.haskellPackages.ghcWithPackages(self: [
+    self.xmonad
+  ] ++ optionals cfg.enableContribAndExtras [ self.xmonadContrib self.xmonadExtras]
+    ++ optionals (cfg.extraPackages != null) (cfg.extraPackages self));
+  xmessage = pkgs.xlibs.xmessage;
 in
-
 {
   options = {
     services.xserver.windowManager.xmonad = {
@@ -13,18 +17,53 @@ in
         example = true;
         description = "Enable the xmonad window manager.";
       };
+
+      haskellPackages = mkOption {
+        default = pkgs.haskellPackages;
+        defaultText = "pkgs.haskellPackages";
+        example = literalExample "pkgs.haskellPackages_ghc701";
+        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 = null;
+        example = literalExample ''
+          haskellPackages: [
+            haskellPackages.xmonadContrib
+            haskellPackages.monadLogger
+          ]
+        '';
+        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;
+        example = true;
+        type = pkgs.lib.types.bool;
+        description = "Enable xmonad-{contrib,extras} in Xmonad.";
+      };
     };
   };
-
-  config = {
+  config = mkIf cfg.enable {
     services.xserver.windowManager = {
-      session = mkIf cfg.enable [{
+      session = [{
         name = "xmonad";
-        start = "
-          ${pkgs.haskellPackages.xmonad}/bin/xmonad &
+        start = ''
+          XMONAD_GHC=${xmonadEnv}/bin/ghc XMONAD_XMESSAGE=${xmessage}/bin/xmessage xmonad &
           waitPID=$!
-        ";
+        '';
       }];
     };
+
+    environment.systemPackages = [ cfg.haskellPackages.xmonad ];
   };
 }

pkgs/applications/window-managers/xmonad/default.nix

@@ -13,6 +13,12 @@ cabal.mkDerivation (self: {
     mkdir -p $out/share/man/man1
     mv $out/share/xmonad-*/man/*.1 $out/share/man/man1/
   '';
+
+  patches = [
+    # Patch to make xmonad use XMONAD_{GHC,XMESSAGE} (if available).
+    ./xmonad_ghc_var_0.11.patch
+  ];
+
   meta = {
     homepage = "http://xmonad.org";
     description = "A tiling window manager";

pkgs/applications/window-managers/xmonad/xmonad_ghc_var_0.11.patch

@@ -0,0 +1,44 @@
+--- xmonad-0.11/XMonad/Core.hs	2013-01-01 01:31:47.000000000 +0000
++++ new-xmonad/XMonad/Core.hs	2013-12-23 17:36:40.862146910 +0000
+@@ -47,6 +47,7 @@
+ import System.Process
+ import System.Directory
+ import System.Exit
++import System.Environment (lookupEnv)
+ import Graphics.X11.Xlib
+ import Graphics.X11.Xlib.Extras (Event)
+ import Data.Typeable
+@@ -452,6 +453,7 @@
+         err  = base ++ ".errors"
+         src  = base ++ ".hs"
+         lib  = dir </> "lib"
++    ghc <- fromMaybe "ghc" <$> liftIO (lookupEnv "XMONAD_GHC")
+     libTs <- mapM getModTime . Prelude.filter isSource =<< allFiles lib
+     srcT <- getModTime src
+     binT <- getModTime bin
+@@ -460,7 +462,7 @@
+         -- temporarily disable SIGCHLD ignoring:
+         uninstallSignalHandlers
+         status <- bracket (openFile err WriteMode) hClose $ \h ->
+-            waitForProcess =<< runProcess "ghc" ["--make", "xmonad.hs", "-i", "-ilib", "-fforce-recomp", "-v0", "-o",binn] (Just dir)
++            waitForProcess =<< runProcess ghc ["--make", "xmonad.hs", "-i", "-ilib", "-fforce-recomp", "-v0", "-o",binn] (Just dir)
+                                     Nothing Nothing Nothing (Just h)
+
+         -- re-enable SIGCHLD:
+@@ -469,6 +471,7 @@
+         -- now, if it fails, run xmessage to let the user know:
+         when (status /= ExitSuccess) $ do
+             ghcErr <- readFile err
++            xmessage <- fromMaybe "xmessage" <$> liftIO (lookupEnv "XMONAD_XMESSAGE")
+             let msg = unlines $
+                     ["Error detected while loading xmonad configuration file: " ++ src]
+                     ++ lines (if null ghcErr then show status else ghcErr)
+@@ -476,7 +479,7 @@
+             -- nb, the ordering of printing, then forking, is crucial due to
+             -- lazy evaluation
+             hPutStrLn stderr msg
+-            forkProcess $ executeFile "xmessage" True ["-default", "okay", msg] Nothing
++            forkProcess $ executeFile xmessage True ["-default", "okay", msg] Nothing
+             return ()
+         return (status == ExitSuccess)
+       else return True