Support displaying floating X windows on all workspaces

; Setting _NET_WM_DESKTOP to 0xffffffff makes an X windows appearing
; on all desktops (EWMH).  It's tricky to do it for tiling X windows
; so it's not implemented.

* exwm-core.el (exwm--desktop): New buffer-local variable recording
the value of _NET_WM_DESKTOP.
* exwm-layout.el (exwm-layout--hide): Do not hide X windows with this
property set to 0xffffffff.

* exwm.el (exwm--update-desktop): New function for fetching the value
of _NET_WM_DESKTOP and setting `exwm--desktop'.
* exwm-manage.el (exwm-manage--manage-window): Use it.

* exwm-workspace.el (exwm-workspace--set-desktop): Also update
`exwm--desktop'.

exwm-core.el

@@ -139,6 +139,7 @@ least SECS seconds later."
 (defvar-local exwm--on-KeyPress         ;KeyPress event handler
   #'exwm-input--on-KeyPress-line-mode)
 ;; Properties
+(defvar-local exwm--desktop nil "_NET_WM_DESKTOP.")
 (defvar-local exwm-window-type nil "_NET_WM_WINDOW_TYPE.")
 (defvar-local exwm--geometry nil)
 (defvar-local exwm-class-name nil "Class name in WM_CLASS.")

exwm-layout.el

@@ -102,7 +102,9 @@
 (defun exwm-layout--hide (id)
   "Hide window ID."
   (with-current-buffer (exwm--id->buffer id)
-    (unless (exwm-layout--iconic-state-p) ;already hidden
+    (unless (or (exwm-layout--iconic-state-p)
+                (and exwm--floating-frame
+                     (eq #xffffffff exwm--desktop)))
       (exwm--log "Hide #x%x" id)
       (when exwm--floating-frame
         (let* ((container (frame-parameter exwm--floating-frame

exwm-manage.el

@@ -73,6 +73,7 @@ You can still make the X windows floating afterwards."
 (declare-function exwm--update-struts "exwm.el" (id))
 (declare-function exwm--update-title "exwm.el" (id))
 (declare-function exwm--update-transient-for "exwm.el" (id &optional force))
+(declare-function exwm--update-desktop "exwm.el" (id &optional force))
 (declare-function exwm--update-window-type "exwm.el" (id &optional force))
 (declare-function exwm-floating--set-floating "exwm-floating.el" (id))
 (declare-function exwm-floating--unset-floating "exwm-floating.el" (id))
@@ -252,19 +253,7 @@ You can still make the X windows floating afterwards."
         (exwm-floating--unset-floating id))
       (exwm-input-grab-keyboard id)
       (setq exwm-workspace--switch-history-outdated t)
-      ;; Set _NET_WM_DESKTOP or move window.
-      (let ((reply (xcb:+request-unchecked+reply exwm--connection
-                       (make-instance 'xcb:ewmh:get-_NET_WM_DESKTOP
-                                      :window id)))
-            desktop)
-        (when reply
-          (setq desktop (slot-value reply 'value)))
-        (if (and desktop
-                 (/= desktop exwm-workspace-current-index)
-                 ;; Check the range.
-                 (< desktop (exwm-workspace--count)))
-            (exwm-workspace-move-window desktop id)
-          (exwm-workspace--set-desktop id)))
+      (exwm--update-desktop id)
       (exwm-manage--update-ewmh-state id)
       (with-current-buffer (exwm--id->buffer id)
         (when (memq xcb:Atom:_NET_WM_STATE_FULLSCREEN exwm--ewmh-state)

exwm-workspace.el

@@ -685,10 +685,12 @@ INDEX must not exceed the current number of workspaces."
 (defun exwm-workspace--set-desktop (id)
   "Set _NET_WM_DESKTOP for X window ID."
   (with-current-buffer (exwm--id->buffer id)
+    (let ((desktop (exwm-workspace--position exwm--frame)))
+      (setq exwm--desktop desktop)
       (xcb:+request exwm--connection
           (make-instance 'xcb:ewmh:set-_NET_WM_DESKTOP
                          :window id
-                       :data (exwm-workspace--position exwm--frame)))))
+                         :data desktop)))))
 
 ;;;###autoload
 (defun exwm-workspace-move-window (frame-or-index &optional id)

exwm.el

@@ -145,6 +145,32 @@
           (while (= ?R (shell-command-on-region (point) (point) args))))
         (kill-emacs))))))
 
+(defun exwm--update-desktop (xwin)
+  "Update _NET_WM_DESKTOP."
+  (with-current-buffer (exwm--id->buffer xwin)
+    (let ((reply (xcb:+request-unchecked+reply exwm--connection
+                     (make-instance 'xcb:ewmh:get-_NET_WM_DESKTOP
+                                    :window xwin)))
+          desktop)
+      (when reply
+        (setq desktop (slot-value reply 'value))
+        (cond
+         ((eq desktop #xffffffff)
+          (unless (or (not exwm--floating-frame)
+                      (eq exwm--frame exwm-workspace--current)
+                      (and exwm--desktop
+                           (= desktop exwm--desktop)))
+            (exwm-layout--show xwin (frame-root-window exwm--floating-frame)))
+          (setq exwm--desktop desktop))
+         ((and desktop
+               (< desktop (exwm-workspace--count))
+               (if exwm--desktop
+                   (/= desktop exwm--desktop)
+                 (/= desktop (exwm-workspace--position exwm--frame))))
+          (exwm-workspace-move-window desktop xwin))
+         (t
+          (exwm-workspace--set-desktop xwin)))))))
+
 (defun exwm--update-window-type (id &optional force)
   "Update _NET_WM_WINDOW_TYPE."
   (with-current-buffer (exwm--id->buffer id)