windowManager.xmonad: Make it configurable and extensible.

PR #1366
The previous windowManager.xmonad option only starts xmonad and
doesn't make ghc available. This assumes that the user has GHC with
access to the xmonad package in his PATH when using xmonad.

Xmonad in Nix is now patched to accept the XMONAD_{GHC,XMESSAGE}
environment variables which define the path to either ghc or xmessage.
These are set automatically when using xmonad through
windowManager.xmonad.

My (or specific: @aristidb and my) changes make it possible to use
Xmonad without adding GHC to any profile. This is useful if you want
to add a different GHC to your profile.

This commit introduces some options:

- xmonad.haskellPackages: Controls which Haskell package set & GHC set
  is used to (re)build Xmonad

- xmonad.extraPackages: Function returning a list of additional
  packages to make available to GHC when rebuilding Xmonad

- xmonad.enableContribExtras: Boolean option to build xmonadContrib
  and xmonadExtras.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>

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>.
+        '';
       };
 
-  config = {
+      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 = mkIf cfg.enable {
     services.xserver.windowManager = {
-      session = mkIf cfg.enable [{
+      session = [{
         name = "xmonad";
-        start = "
+        start = ''
-          ${pkgs.haskellPackages.xmonad}/bin/xmonad &
+          XMONAD_GHC=${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