X.H.EwmhDesktops: Added customization for external desktop switching.

Added a configuration option to change the action for handling the
_NET_CURRENT_DESKTOP requests.

XMonad/Hooks/EwmhDesktops.hs

@@ -42,6 +42,10 @@ module XMonad.Hooks.EwmhDesktops (
     -- $customActivate
     setEwmhActivateHook,
 
+    -- ** External workspace switching
+    -- $customWorkspaceSwitch
+    setEwmhSwitchDesktopAction,
+
     -- ** Fullscreen
     -- $customFullscreen
     setEwmhFullscreenHooks,
@@ -114,6 +118,8 @@ data EwmhDesktopsConfig =
             -- ^ configurable handling of window activation requests
         , fullscreenHooks :: (ManageHook, ManageHook)
             -- ^ configurable handling of fullscreen state requests
+        , switchDesktopAction :: WorkspaceId -> WindowSet -> WindowSet
+            -- ^ configurable action for handling _NET_CURRENT_DESKTOP
         , manageDesktopViewport :: Bool
             -- ^ manage @_NET_DESKTOP_VIEWPORT@?
         }
@@ -124,6 +130,7 @@ instance Default EwmhDesktopsConfig where
         , workspaceRename = pure pure
         , activateHook = doFocus
         , fullscreenHooks = (doFullFloat, doSink)
+        , switchDesktopAction = W.view
         , manageDesktopViewport = True
         }
 
@@ -245,6 +252,22 @@ setEwmhActivateHook :: ManageHook -> XConfig l -> XConfig l
 setEwmhActivateHook h = XC.modifyDef $ \c -> c{ activateHook = h }
 
 
+-- $customWorkspaceSwitch
+-- When a client sends a @_NET_CURRENT_DESKTOP@ request to switch to a workspace,
+-- the default action used to do that is the 'W.view' function.
+-- This may not be the desired behaviour in all configurations.
+--
+-- For example if using the "XMonad.Layout.IndependentScreens" the default action
+-- might move a workspace to a screen that it isn't supposed to be on.
+--
+-- > -- TODO add code example
+
+-- | Set (replace) the action which is invoked when a client sends a
+-- @_NET_CURRENT_DESKTOP@ request to switch workspace.
+setEwmhSwitchDesktopAction :: (WorkspaceId -> WindowSet -> WindowSet) -> XConfig l -> XConfig l
+setEwmhSwitchDesktopAction action = XC.modifyDef $ \c -> c{ switchDesktopAction = action }
+
+
 -- $customFullscreen
 -- When a client sends a @_NET_WM_STATE@ request to add\/remove\/toggle the
 -- @_NET_WM_STATE_FULLSCREEN@ state, 'ewmhFullscreen' uses a pair of hooks to
@@ -449,7 +472,7 @@ mkViewPorts winset = setDesktopViewport . concat . mapMaybe (viewPorts M.!?)
 ewmhDesktopsEventHook' :: Event -> EwmhDesktopsConfig -> X All
 ewmhDesktopsEventHook'
         ClientMessageEvent{ev_window = w, ev_message_type = mt, ev_data = d}
-        EwmhDesktopsConfig{workspaceSort, activateHook} =
+        EwmhDesktopsConfig{workspaceSort, activateHook, switchDesktopAction} =
     withWindowSet $ \s -> do
         sort' <- workspaceSort
         let ws = sort' $ W.workspaces s
@@ -462,7 +485,7 @@ ewmhDesktopsEventHook'
         if  | mt == a_cw ->
                 killWindow w
             | mt == a_cd, n : _ <- d, Just ww <- ws !? fi n ->
-                if W.currentTag s == W.tag ww then mempty else windows $ W.view (W.tag ww)
+                if W.currentTag s == W.tag ww then mempty else windows $ switchDesktopAction (W.tag ww)
             | mt == a_cd ->
                 trace $ "Bad _NET_CURRENT_DESKTOP with data=" ++ show d
             | not (w `W.member` s) ->