[MINOR] made xmonad focus monitor on hover, even if empty

.config/xmonad/xmonad.hs

@@ -26,6 +26,14 @@ import XMonad.Actions.UpdateFocus (focusUnderPointer)
 import XMonad.Layout.NoBorders
 import XMonad.Layout.Spacing
 
+
+-- MultiMonitorFocusHook
+import Control.Monad (when)
+import Data.Foldable (find)
+import Foreign.C (CInt)
+import Data.Maybe (fromMaybe)
+import Data.Monoid (All (All))
+
 --Miscellaneous
 import qualified XMonad.StackSet as W
 import qualified Data.Map        as M
@@ -140,6 +148,33 @@ myManageHook = composeAll
   , isFullscreen -->  doFullFloat]
 
 myEventHook = ewmhDesktopsEventHook
+
+
+multiScreenFocusHook :: Event -> X All
+multiScreenFocusHook MotionEvent { ev_x = x, ev_y = y } = do
+  ms <- getScreenForPos x y
+  let cursorScreenID = W.screen <$> ms
+  focussedScreenID <- W.screen . W.current . windowset <$> get
+  when (cursorScreenID /= Just focussedScreenID) $
+    maybe (return ()) (windows . W.view . W.tag . W.workspace) ms
+  return (All True)
+  where
+    getScreenForPos :: CInt -> CInt
+      -> X (Maybe (W.Screen WorkspaceId (Layout Window) Window ScreenId ScreenDetail))
+    getScreenForPos x y = do
+      ws <- windowset <$> get
+      let screens = W.current ws : W.visible ws
+          inRects = map (inRect x y . screenRect . W.screenDetail) screens
+      return $ fst <$> find snd (zip screens inRects)
+
+    inRect :: CInt -> CInt -> Rectangle -> Bool
+    inRect x y rect =
+      let l = fromIntegral (rect_x rect)
+          r = l + fromIntegral (rect_width rect)
+          t = fromIntegral (rect_y rect)
+          b = t + fromIntegral (rect_height rect)
+      in x >= l && x < r && y >= t && y < b
+
 myStartupHook = do
       spawnOnce "pasystray"
       spawnOnce "nitrogen --restore &"
@@ -190,6 +225,7 @@ myXmobarPP s  =  def
 
 myConfig =  def
       {
+      rootMask           = rootMask def .|. pointerMotionMask,
       terminal           = myTerminal,
       focusFollowsMouse  = myFocusFollowsMouse,
       clickJustFocuses   = myClickJustFocuses,
@@ -201,7 +237,7 @@ myConfig =  def
      -- keys               = myKeys,
       layoutHook         = smartBorders . spacingWithEdge 10 $ myLayout,
       manageHook         = manageSpawn <+> myManageHook <+> manageHook def,
-      handleEventHook    = myEventHook <+> fullscreenEventHook <+> swallowEventHook (className=?"Alacritty") (return True) ,
+      handleEventHook    = myEventHook <+> multiScreenFocusHook <+> fullscreenEventHook <+> swallowEventHook (className=?"Alacritty") (return True),
       startupHook        = myStartupHook
       }