Improve detection of focus changes

	* exwm-input.el: (exwm-input--on-buffer-list-update): Keep track
	of last selected window and buffer, update focus only when those
	change.
	(exwm-input--update-focus-defer): Add commentary.
	(exwm-input--buffer-list-update-last-selected-window)
	(exwm-input--buffer-list-update-last-selected-buffer): Add
	variables.
	(exwm-input--skip-buffer-list-update): Remove variable.
	(exwm-input--on-buffer-list-update): Stop checking
	`exwm-input--skip-buffer-list-update'; it's no longer needed when
	keeping track selected window and buffer.

	* exwm-manage.el (exwm-manage--manage-window): Remove binding of
	`exwm-input--skip-buffer-list-update'.

exwm-input.el

@@ -117,9 +117,6 @@ defined in `exwm-mode-map' here."
 
 (defvar exwm-input--simulation-keys nil "Simulation keys in line-mode.")
 
-(defvar exwm-input--skip-buffer-list-update nil
-  "Skip the upcoming 'buffer-list-update'.")
-
 (defvar exwm-input--temp-line-mode nil
   "Non-nil indicates it's in temporary line-mode for char-mode.")
 
@@ -140,6 +137,12 @@ defined in `exwm-mode-map' here."
 (defvar exwm-input--update-focus-window nil "The (Emacs) window to be focused.
 This value should always be overwritten.")
 
+(defvar exwm-input--last-selected-window nil
+  "Last selected window.  Help us discern cause of `buffer-list-update-hook'.")
+
+(defvar exwm-input--last-selected-buffer nil
+  "Last selected window.  Help us discern cause of `buffer-list-update-hook'.")
+
 (defvar exwm-input--echo-area-timer nil "Timer for detecting echo area dirty.")
 
 (defvar exwm-input--event-hook nil
@@ -292,13 +295,25 @@ ARGS are additional arguments to CALLBACK."
 
 (defun exwm-input--on-buffer-list-update ()
   "Run in `buffer-list-update-hook' to track input focus."
-  (when (and (not (exwm-workspace--client-p))
-             (not exwm-input--skip-buffer-list-update))
-    (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)))
+  ;; `buffer-list-update-hook' is invoked by several functions
+  ;; (`get-buffer-create', `select-window', `with-temp-buffer', etc.), but we
+  ;; just want to notice when a different window has been selected, or when the
+  ;; selected window displays a different buffer, so that we can set the focus
+  ;; to the associated X window (in case of an `exwm-mode' buffer).  In order to
+  ;; differentiate, we keep track of the last selected window and buffer in the
+  ;; `exwm-input--last-selected-window' and
+  ;; `exwm-input--last-selected-buffer' variables.
+  (let* ((win (selected-window))
+         (buf (window-buffer win)))
+    (when (and (not (exwm-workspace--client-p))
+               (not (and (eq exwm-input--last-selected-window win)
+                         (eq exwm-input--last-selected-buffer buf))))
+      (setq exwm-input--last-selected-window win)
+      (setq exwm-input--last-selected-buffer buf)
+      (exwm--log "selected-window=%S current-buffer=%S" win buf)
+      (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."

exwm-manage.el

@@ -151,7 +151,6 @@ want to match against EXWM internal variables such as `exwm-title',
 (defvar exwm-manage--ping-lock nil
   "Non-nil indicates EXWM is pinging a window.")
 
-(defvar exwm-input--skip-buffer-list-update)
 (defvar exwm-input-prefix-keys)
 (defvar exwm-workspace--current)
 (defvar exwm-workspace--id-struts-alist)
@@ -263,8 +262,7 @@ want to match against EXWM internal variables such as `exwm-title',
         (make-instance 'xcb:ChangeSaveSet
                        :mode xcb:SetMode:Insert
                        :window id))
-    (with-current-buffer (let ((exwm-input--skip-buffer-list-update t))
-                           (generate-new-buffer "*EXWM*"))
+    (with-current-buffer (generate-new-buffer "*EXWM*")
       ;; Keep the oldest X window first.
       (setq exwm--id-buffer-alist
             (nconc exwm--id-buffer-alist `((,id . ,(current-buffer)))))
@@ -349,8 +347,7 @@ want to match against EXWM internal variables such as `exwm-title',
                              :stack-mode xcb:StackMode:Below)))
         (xcb:flush exwm--connection)
         (setq exwm--id-buffer-alist (assq-delete-all id exwm--id-buffer-alist))
-        (let ((kill-buffer-query-functions nil)
-              (exwm-input--skip-buffer-list-update t))
+        (let ((kill-buffer-query-functions nil))
           (kill-buffer (current-buffer)))
         (throw 'return 'ignored))
       (let ((index (plist-get exwm--configurations 'workspace)))