Revert "Add undelete-frame-max instead of undelete-frame-mode (bug#51883)"

This reverts commit 714e11d535.

That commit was unilateral and disregarded past discussions.

doc/emacs/frames.texi

@@ -515,14 +515,12 @@ error if there is only one frame.
 @item C-x 5 u
 @kindex C-x 5 u
 @findex undelete-frame
-@findex undelete-frame-max
-Undelete one of the recently deleted frames.  The user option
-@code{undelete-frame-max} specifies the maximum number of deleted
-frames to keep (the default is 1).  Without a prefix argument,
-undelete the most recently deleted frame.  With a numerical prefix
-argument between 1 and the number specified by @code{undelete-frame-max},
-where 1 is the most recently deleted frame, undelete the corresponding
-deleted frame.
+@findex undelete-frame-mode
+When @code{undelete-frame-mode} is enabled, undelete one of the 16
+most recently deleted frames.  Without a prefix argument, undelete the
+most recently deleted frame.  With a numerical prefix argument between
+1 and 16, where 1 is the most recently deleted frame, undelete the
+corresponding deleted frame.
 
 @item C-z
 @kindex C-z @r{(X windows)}

etc/NEWS

@@ -287,12 +287,11 @@ height use 'window-height' in combination with 'body-lines'.
 
 +++
 *** Deleted frames can now be undeleted.
-The most recently deleted frame can be undeleted with 'C-x 5 u' when
-the new user option 'undelete-frame-max' has its default value 1.
-Without a prefix argument, undelete the most recently deleted frame.
-With a numerical prefix argument between 1 and 'undelete-frame-max',
-where 1 is the most recently deleted frame, undelete the corresponding
-deleted frame.
+The 16 most recently deleted frames can be undeleted with 'C-x 5 u' when
+'undelete-frame-mode' is enabled.  Without a prefix argument, undelete
+the most recently deleted frame.  With a numerical prefix argument
+between 1 and 16, where 1 is the most recently deleted frame, undelete
+the corresponding deleted frame.
 
 ** Tab Bars and Tab Lines
 

lisp/frame.el

@@ -2529,13 +2529,6 @@ deleting them."
         (if iconify (iconify-frame this) (delete-frame this)))
       (setq this next))))
 
-
-(defcustom undelete-frame-max 1
-  "Maximum number of deleted frames before oldest are thrown away."
-  :type 'integer
-  :group 'frames
-  :version "29.1")
-
 (eval-when-compile (require 'frameset))
 
 (defvar undelete-frame--deleted-frames nil
@@ -2543,7 +2536,7 @@ deleting them."
 
 (defun undelete-frame--handle-delete-frame (frame)
   "Save the configuration of frames deleted with `delete-frame'.
-Only the `undelete-frame-max' most recently deleted frames are saved."
+Only the 16 most recently deleted frames are saved."
   (when (frame-live-p frame)
     (setq undelete-frame--deleted-frames
           (cons
@@ -2562,45 +2555,54 @@ Only the `undelete-frame-max' most recently deleted frames are saved."
                         (cons '(display . :never)
                               frameset-filter-alist))))
            undelete-frame--deleted-frames))
-    (if (> (length undelete-frame--deleted-frames) undelete-frame-max)
+    (if (> (length undelete-frame--deleted-frames) 16)
         (setq undelete-frame--deleted-frames
               (butlast undelete-frame--deleted-frames)))))
 
-(add-hook 'after-init-hook
-          (lambda ()
-            (add-hook 'delete-frame-functions
-                      #'undelete-frame--handle-delete-frame -75)))
+(define-minor-mode undelete-frame-mode
+  "Enable the `undelete-frame' command."
+  :group 'frames
+  :global t
+  (if undelete-frame-mode
+      (add-hook 'delete-frame-functions
+                #'undelete-frame--handle-delete-frame -75)
+    (remove-hook 'delete-frame-functions
+                 #'undelete-frame--handle-delete-frame)
+    (setq undelete-frame--deleted-frames nil)))
 
 (defun undelete-frame (&optional arg)
   "Undelete a frame deleted with `delete-frame'.
-Without a prefix argument, undelete the most recently deleted frame.
-With a numerical prefix argument ARG between 1 and `undelete-frame-max',
-where 1 is most recently deleted frame, undelete the ARGth deleted frame.
+Without a prefix argument, undelete the most recently deleted
+frame.
+With a numerical prefix argument ARG between 1 and 16, where 1 is
+most recently deleted frame, undelete the ARGth deleted frame.
 When called from Lisp, returns the new frame."
   (interactive "P")
-  (if (consp arg)
-      (user-error "Missing deleted frame number argument")
-    (let* ((number (pcase arg ('nil 1) ('- -1) (_ arg)))
-           (frames (frame-list))
-           (frameset (nth (1- number) undelete-frame--deleted-frames))
-           (graphic (display-graphic-p)))
-      (if (not (<= 1 number undelete-frame-max))
-          (user-error "%d is not a valid deleted frame number argument"
-                      number)
-        (if (not frameset)
-            (user-error "No deleted frame with number %d" number)
-          (if (not (eq graphic (car frameset)))
-              (user-error
-               "Cannot undelete a %s display frame on a %s display"
-               (if graphic "non-graphic" "graphic")
-               (if graphic "graphic" "non-graphic"))
-            (setq undelete-frame--deleted-frames
-                  (delq frameset undelete-frame--deleted-frames))
-            (frameset-restore (cdr frameset))
-            (let ((frame (car (seq-difference (frame-list) frames))))
-              (when frame
-                (select-frame-set-input-focus frame)
-                frame))))))))
+  (if (not undelete-frame-mode)
+      (user-error "Undelete-Frame mode is disabled")
+    (if (consp arg)
+        (user-error "Missing deleted frame number argument")
+      (let* ((number (pcase arg ('nil 1) ('- -1) (_ arg)))
+             (frames (frame-list))
+             (frameset (nth (1- number) undelete-frame--deleted-frames))
+             (graphic (display-graphic-p)))
+        (if (not (<= 1 number 16))
+            (user-error "%d is not a valid deleted frame number argument"
+                        number)
+          (if (not frameset)
+              (user-error "No deleted frame with number %d" number)
+            (if (not (eq graphic (car frameset)))
+                (user-error
+                 "Cannot undelete a %s display frame on a %s display"
+                 (if graphic "non-graphic" "graphic")
+                 (if graphic "graphic" "non-graphic"))
+              (setq undelete-frame--deleted-frames
+                    (delq frameset undelete-frame--deleted-frames))
+              (frameset-restore (cdr frameset))
+              (let ((frame (car (seq-difference (frame-list) frames))))
+                (when frame
+                  (select-frame-set-input-focus frame)
+                  frame)))))))))
 
 ;;; Window dividers.
 (defgroup window-divider nil

lisp/menu-bar.el

@@ -109,9 +109,14 @@
       (bindings--define-key menu [separator-tab]
         menu-bar-separator))
 
+    (bindings--define-key menu [enable-undelete-frame-mode]
+      '(menu-item "Enable Undeleting Frames" undelete-frame-mode
+                  :visible (null undelete-frame-mode)
+                  :help "Enable undeleting frames in this session"))
     (bindings--define-key menu [undelete-last-deleted-frame]
       '(menu-item "Undelete Frame" undelete-frame
-                  :visible (car undelete-frame--deleted-frames)
+                  :visible (and undelete-frame-mode
+                                (car undelete-frame--deleted-frames))
                   :help "Undelete the most recently deleted frame"))
 
     ;; Don't use delete-frame as event name because that is a special

src/frame.c

@@ -2385,7 +2385,7 @@ DEFUN ("delete-frame", Fdelete_frame, Sdelete_frame, 0, 2, "",
        doc: /* Delete FRAME, eliminating it from use.
 FRAME must be a live frame and defaults to the selected one.
 
-When `undelete-frame-max' is more than 0, the most recently deleted
+When `undelete-frame-mode' is enabled, the 16 most recently deleted
 frames can be undeleted with `undelete-frame', which see.
 
 A frame may not be deleted if its minibuffer serves as surrogate