refactor(3p/exwm): Simplify and improve focus handling

- No need for two different timers, roll them into one.
- Debounce focus updates.
- Handle "no focus" frames.

Depot note: This patch was taken from Sibalien's fork of EXWM, and I'm
experimentally adding it here to see if it has any effect on wonkiness
around focusing.

Change-Id: Ifabfccc80817daabedd31e51532aef3c4277e2ed
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10046
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

third_party/exwm/exwm-input.el

@@ -129,17 +129,12 @@ defined in `exwm-mode-map' here."
 
 (defvar exwm-input--timestamp-window nil)
 
-(defvar exwm-input--update-focus-defer-timer nil "Timer for polling the lock.")
-
 (defvar exwm-input--update-focus-lock nil
   "Lock for solving input focus update contention.")
 
 (defvar exwm-input--update-focus-timer nil
   "Timer for deferring the update of input focus.")
 
-(defvar exwm-input--update-focus-window nil "The (Emacs) window to be focused.
-This value should always be overwritten.")
-
 (defvar exwm-input--echo-area-timer nil "Timer for detecting echo area dirty.")
 
 (defvar exwm-input--event-hook nil
@@ -299,18 +294,11 @@ ARGS are additional arguments to CALLBACK."
          (exwm--terminal-p))      ; skip other terminals, e.g. TTY client frames
     (exwm--log "current-buffer=%S selected-window=%S"
                (current-buffer) (selected-window))
-    (redirect-frame-focus (selected-frame) nil)
-    (setq exwm-input--update-focus-window (selected-window))
     (exwm-input--update-focus-defer)))
 
 (defun exwm-input--update-focus-defer ()
   "Defer updating input focus."
-  (when exwm-input--update-focus-defer-timer
+  (redirect-frame-focus (selected-frame) nil)
-    (cancel-timer exwm-input--update-focus-defer-timer))
-  (if exwm-input--update-focus-lock
-      (setq exwm-input--update-focus-defer-timer
-            (exwm--defer 0 #'exwm-input--update-focus-defer))
-    (setq exwm-input--update-focus-defer-timer nil)
   (when exwm-input--update-focus-timer
     (cancel-timer exwm-input--update-focus-timer))
   (setq exwm-input--update-focus-timer
@@ -318,18 +306,23 @@ ARGS are additional arguments to CALLBACK."
         (run-with-timer exwm-input--update-focus-interval
                         nil
                         #'exwm-input--update-focus-commit
-                          exwm-input--update-focus-window))))
+                        (selected-window))))
 
 (defun exwm-input--update-focus-commit (window)
   "Commit updating input focus."
-  (setq exwm-input--update-focus-lock t)
+  (let ((cwin (selected-window)))
-  (unwind-protect
+    (if exwm-input--update-focus-lock
-      (exwm-input--update-focus window)
+        (unless (eq exwm-input--update-focus-lock cwin)
-    (setq exwm-input--update-focus-lock nil)))
+          (exwm-input--update-focus-defer))
+      (if (and cwin window (eq cwin window))
+          (let ((exwm-input--update-focus-lock cwin))
+            (exwm-input--update-focus window))
+        (exwm-input--update-focus-defer)))))
 
 (defun exwm-input--update-focus (window)
   "Update input focus."
-  (when (window-live-p window)
+  (when  (and (window-live-p window)
+              (not (frame-parameter (window-frame window) 'no-accept-focus)))
     (exwm--log "focus-window=%s focus-buffer=%s" window (window-buffer window))
     (with-current-buffer (window-buffer window)
       (if (derived-mode-p 'exwm-mode)
@@ -1233,8 +1226,6 @@ One use is to access the keymap bound to KEYS (as prefix keys) in `char-mode'."
     (setq exwm-input--echo-area-timer nil))
   (remove-hook 'echo-area-clear-hook #'exwm-input--on-echo-area-clear)
   (remove-hook 'buffer-list-update-hook #'exwm-input--on-buffer-list-update)
-  (when exwm-input--update-focus-defer-timer
-    (cancel-timer exwm-input--update-focus-defer-timer))
   (when exwm-input--update-focus-timer
     (cancel-timer exwm-input--update-focus-timer))
   ;; Make input focus working even without a WM.