X.A.Submap: establish pointer grab to avoid freezing X.

Establish active asynchronous pointer grab before entering infinity cycle.
Because xmonad already has passive synchronous pointer grab, this overwrites
it temporary and avoids freezing X, when button press occurs after submap key
press.

Also, terminate submap at button press in the same way, as we do for wrong key
press.

CHANGES.md

@@ -42,6 +42,12 @@
     EWMH taskbars and pagers. Useful for `NamedScratchpad` windows, since
     you will usually be taken to the `NSP` workspace by them.
 
+  * `XMonad.Actions.Submap`
+
+    Establish pointer grab to avoid freezing X, when button press occurs after
+    submap key press.  And terminate submap at button press in the same way,
+    as we do for wrong key press.
+
 ### Minor Changes
 
   * `XMonad.Layout.LayoutBuilder`

XMonad/Actions/Submap.hs

@@ -75,17 +75,23 @@ submapDefaultWithKey defAction keys = do
     XConf { theRoot = root, display = d } <- ask
 
     io $ grabKeyboard d root False grabModeAsync grabModeAsync currentTime
+    io $ grabPointer d root False buttonPressMask grabModeAsync grabModeAsync
+                     none none currentTime
 
     (m, s) <- io $ allocaXEvent $ \p -> fix $ \nextkey -> do
-        maskEvent d keyPressMask p
-        KeyEvent { ev_keycode = code, ev_state = m } <- getEvent p
-        keysym <- keycodeToKeysym d code 0
-        if isModifierKey keysym
-            then nextkey
-            else return (m, keysym)
+        maskEvent d (keyPressMask .|. buttonPressMask) p
+        ev <- getEvent p
+        case ev of
+          KeyEvent { ev_keycode = code, ev_state = m } -> do
+            keysym <- keycodeToKeysym d code 0
+            if isModifierKey keysym
+                then nextkey
+                else return (m, keysym)
+          _ -> return (0, 0)
     -- Remove num lock mask and Xkb group state bits
     m' <- cleanMask $ m .&. ((1 `shiftL` 12) - 1)
 
+    io $ ungrabPointer d currentTime
     io $ ungrabKeyboard d currentTime
 
     fromMaybe (defAction (m', s)) (M.lookup (m', s) keys)