Fix several todo-mode.el item editing bugs (bug#63811)

* lisp/calendar/todo-mode.el (todo-insert-item--basic): With
insertion type 'here', ensure item is inserted on the todo-mode
line where the command was invoked.
(todo-edit-item--cat, todo-edit-item--pos): New variables.
(todo-edit-item--text): Restrict the scope of nil-valued
buffer-read-only to the functions that change buffer text.  If
user moved point while editing a single-line todo item or a done
item comment, or while inserting a done item comment, restore
point, and for comments, make sure the done items section is
displayed.  For multiline items, set the new variables so
todo-edit-quit can use them.
(todo-edit-quit): Use the values of the new variables to restore
point in the todo-mode buffer if it had been moved while editing.
(todo-edit-item--header): Avoid clobbering match data when editing
a todo item header.

lisp/calendar/todo-mode.el

@@ -1985,7 +1985,13 @@ their associated keys and their effects."
 		  (setq done-only t)
 		  (todo-toggle-view-done-only))
 		(if here
-                    (todo-insert-with-overlays new-item)
+		    (progn
+		      ;; Ensure item is inserted where command was invoked.
+		      (unless (= (point) opoint)
+			(todo-category-number ocat)
+			(todo-category-select)
+			(goto-char opoint))
+                      (todo-insert-with-overlays new-item))
 		  (todo-set-item-priority new-item cat t))
 		(setq item-added t))
 	    ;; If user cancels before setting priority, restore
@@ -2119,6 +2125,9 @@ the item at point."
 	  ((or marked (todo-item-string))
 	   (todo-edit-item--next-key 'todo arg)))))
 
+(defvar todo-edit-item--cat nil)
+(defvar todo-edit-item--pos nil)
+
 (defun todo-edit-item--text (&optional arg)
   "Function providing the text editing facilities of `todo-edit-item'."
   (let ((full-item (todo-item-string)))
@@ -2127,6 +2136,7 @@ the item at point."
     ;; 1+ signals an error, so just make this a noop.
     (when full-item
       (let* ((opoint (point))
+	     (ocat (todo-current-category))
 	     (start (todo-item-start))
 	     (end (save-excursion (todo-item-end)))
 	     (item-beg (progn
@@ -2151,8 +2161,7 @@ the item at point."
 			 (concat " \\[" (regexp-quote todo-comment-string)
 				 ": \\([^]]+\\)\\]")
                          end t)))
-	     (prompt (if comment "Edit comment: " "Enter a comment: "))
+	     (prompt (if comment "Edit comment: " "Enter a comment: ")))
-	     (buffer-read-only nil))
 	;; When there are marked items, user can invoke todo-edit-item
 	;; even if point is not on an item, but text editing only
 	;; applies to the item at point.
@@ -2170,22 +2179,43 @@ the item at point."
                                      end t)
 		  (if comment-delete
 		      (when (todo-y-or-n-p "Delete comment? ")
-			(delete-region (match-beginning 0) (match-end 0)))
+			(let ((buffer-read-only nil))
+			  (delete-region (match-beginning 0) (match-end 0))))
+		    (let ((buffer-read-only nil))
 		      (replace-match (save-match-data
-                                     (read-string prompt
+				       (prog1 (let ((buffer-read-only t))
+						(read-string
+						 prompt
 						 (cons (match-string 1) 1)))
-				   nil nil nil 1))
+					 ;; If user moved point while editing
+					 ;; a comment, restore it and ensure
+					 ;; done items section is displayed.
+					 (unless (= (point) opoint)
+					   (todo-category-number ocat)
+					   (let ((todo-show-with-done t))
+					     (todo-category-select)
+					     (goto-char opoint)))))
+				     nil nil nil 1)))
 		(if comment-delete
 		    (user-error "There is no comment to delete")
+		  (let ((buffer-read-only nil))
 		    (insert " [" todo-comment-string ": "
-			  (prog1 (read-string prompt)
+			    (prog1 (let ((buffer-read-only t))
-			    ;; If user moved point during editing,
+				     (read-string prompt))
-			    ;; make sure it moves back.
+			      ;; If user moved point while inserting a
-			    (goto-char opoint)
+			      ;; comment, restore it and ensure done items
+			      ;; section is displayed.
+			      (unless (= (point) opoint)
+				(todo-category-number ocat)
+				(let ((todo-show-with-done t))
+				  (todo-category-select)
+				  (goto-char opoint)))
 			      (todo-item-end))
-			  "]")))))
+			    "]"))))))
 	   (multiline
 	    (let ((buf todo-edit-buffer))
+	      (setq todo-edit-item--cat ocat)
+	      (setq todo-edit-item--pos opoint)
 	      (set-window-buffer (selected-window)
 				 (set-buffer (make-indirect-buffer
 					      (buffer-name) buf)))
@@ -2208,10 +2238,14 @@ the item at point."
 	      ;; Ensure lines following hard newlines are indented.
 	      (setq new (replace-regexp-in-string "\\(\n\\)[^[:blank:]]"
 						  "\n\t" new nil nil 1))
-	      ;; If user moved point during editing, make sure it moves back.
+	      ;; If user moved point while editing item, restore it.
-	      (goto-char opoint)
+	      (unless (= (point) opoint)
+		(todo-category-number ocat)
+		(todo-category-select)
+		(goto-char opoint))
+	      (let ((buffer-read-only nil))
 		(todo-remove-item)
-	      (todo-insert-with-overlays new)
+		(todo-insert-with-overlays new))
 	      (move-to-column item-beg)))))))))
 
 (defun todo-edit-quit ()
@@ -2243,6 +2277,9 @@ made in the number or names of categories."
 	(kill-buffer)
 	(unless (eq (current-buffer) buf)
 	  (set-window-buffer (selected-window) (set-buffer buf)))
+	(todo-category-number todo-edit-item--cat)
+	(todo-category-select)
+	(goto-char todo-edit-item--pos)
         (if transient-mark-mode (deactivate-mark)))
     ;; We got here via `F e'.
     (when (todo-check-format)
@@ -2315,17 +2352,18 @@ made in the number or names of categories."
 	    ;; If there are marked items, use only the first to set
 	    ;; header changes, and apply these to all marked items.
 	    (when first
+	      (save-match-data
 		(cond
 		 ((eq what 'date)
 		  (setq ndate (todo-read-date)))
 		 ((eq what 'calendar)
-		(setq ndate (save-match-data (todo-set-date-from-calendar))))
+		  (setq ndate (todo-set-date-from-calendar)))
 		 ((eq what 'today)
 		  (setq ndate (calendar-date-string (calendar-current-date) t t)))
 		 ((eq what 'dayname)
 		  (setq ndate (todo-read-dayname)))
 		 ((eq what 'time)
-		(setq ntime (save-match-data (todo-read-time)))
+		  (setq ntime (todo-read-time))
 		  (when (> (length ntime) 0)
 		    (setq ntime (concat " " ntime))))
 		 ;; When date string consists only of a day name,
@@ -2425,7 +2463,7 @@ made in the number or names of categories."
 				    (setq month (number-to-string adjmm))
 				  (setq monthname (aref tma-array (1- adjmm))))
 				;; Return changed numerical day as a string.
-			      (number-to-string (nth 1 date)))))))))
+				(number-to-string (nth 1 date))))))))))
 	    (unless odayname
 	      ;; If year, month or day date string components were
 	      ;; changed, rebuild the date string.