Avoid making todo-mode buffers manually editable

* lisp/calendar/todo-mode.el (todo-add-category)
(todo-move-category, todo-edit-item--header)
(todo-set-item-priority, todo-move-item, todo-item-undone)
(todo-archive-done-item, todo-set-category-number): Restrict the
scope of nil buffer-read-only to the function calls that change
buffer text, thereby preventing todo mode buffers from becoming
manually editable and hence possibly corrupted when the minibuffer
is in use.

lisp/calendar/todo-mode.el

@@ -1294,15 +1294,15 @@ return the new category number."
 		    file)))
     (find-file file0)
     (let ((counts (make-vector 4 0))	; [todo diary done archived]
-	  (num (1+ (length todo-categories)))
-	  (buffer-read-only nil))
+	  (num (1+ (length todo-categories))))
       (setq todo-current-todo-file file0)
       (setq todo-categories (append todo-categories
 				     (list (cons cat counts))))
       (widen)
       (goto-char (point-max))
       (save-excursion			; Save point for todo-category-select.
-	(insert todo-category-beg cat "\n\n" todo-category-done "\n"))
+	(let ((buffer-read-only nil))
+	  (insert todo-category-beg cat "\n\n" todo-category-done "\n")))
       (todo-update-categories-sexp)
       ;; If invoked by user, display the newly added category, if
       ;; called programmatically return the category number to the
@@ -1459,8 +1459,7 @@ the archive of the file moved to, creating it if it does not exist."
 			  (match-beginning 0)
 			(point-max)))
 		 (content (buffer-substring-no-properties beg end))
-		 (counts (cdr (assoc cat todo-categories)))
-		 buffer-read-only)
+		 (counts (cdr (assoc cat todo-categories))))
 	    ;; Move the category to the new file.  Also update or create
 	    ;; archive file if necessary.
 	    (with-current-buffer
@@ -1520,6 +1519,7 @@ the archive of the file moved to, creating it if it does not exist."
 	    ;; Delete the category from the old file, and if that was the
 	    ;; last category, delete the file.  Also handle archive file
 	    ;; if necessary.
+	    (let ((buffer-read-only nil))
 	      (remove-overlays beg end)
 	      (delete-region beg end)
 	      (goto-char (point-min))
@@ -1538,7 +1538,7 @@ the archive of the file moved to, creating it if it does not exist."
 		(todo-update-categories-sexp)
 		(when (> todo-category-number (length todo-categories))
 		  (setq todo-category-number 1))
-	      (todo-category-select)))))
+		(todo-category-select))))))
       (set-window-buffer (selected-window)
 			 (set-buffer (find-file-noselect nfile))))))
 
@@ -2314,7 +2314,6 @@ made in the number or names of categories."
 	;; INC must be an integer, but users could pass it via
 	;; `todo-edit-item' as e.g. `-' or `C-u'.
 	(inc (prefix-numeric-value inc))
-	(buffer-read-only nil)
 	ndate ntime
         year monthname month day) ;; dayname
     (when marked (todo--user-error-if-marked-done-item))
@@ -2477,13 +2476,14 @@ made in the number or names of categories."
                            (day day)
                            (dayname nil)) ;; dayname
                         (mapconcat #'eval calendar-date-display-form "")))))
+	    (let ((buffer-read-only nil))
 	      (when ndate (replace-match ndate nil nil nil 1))
 	      ;; Add new time string to the header, if it was supplied.
 	      (when ntime
 		(if otime
 		    (replace-match ntime nil nil nil 2)
 		  (goto-char (match-end 1))
-		(insert ntime)))
+		  (insert ntime))))
 	    (setq todo-date-from-calendar nil)
 	    (setq first nil))
 	  ;; Apply the changes to the first marked item header to the
@@ -2650,8 +2650,7 @@ meaning to raise or lower the item's priority by one."
 			    (1- curnum))
 			   ((and (eq arg 'lower) (<= curnum maxnum))
 			    (1+ curnum))))
-	   candidate
-	   buffer-read-only)
+	   candidate)
       (unless (and priority
 		   (or (and (eq arg 'raise) (zerop priority))
 		       (and (eq arg 'lower) (> priority maxnum))))
@@ -2704,6 +2703,7 @@ meaning to raise or lower the item's priority by one."
 	    (when match
 	      (user-error (concat "Cannot reprioritize items from the same "
 				  "category in this mode, only in Todo mode")))))
+	(let ((buffer-read-only nil))
 	  ;; Interactively or with non-nil ARG, relocate the item within its
 	  ;; category.
 	  (when (or arg (called-interactively-p 'any))
@@ -2712,10 +2712,9 @@ meaning to raise or lower the item's priority by one."
 	  (when priority
 	    (unless (= priority 1)
 	      (todo-forward-item (1- priority))
-	    ;; When called from todo-item-undone and the highest priority
-	    ;; is chosen, this advances point to the first done item, so
-	    ;; move it up to the empty line above the done items
-	    ;; separator.
+	      ;; When called from todo-item-undone and the highest priority is
+	      ;; chosen, this advances point to the first done item, so move
+	      ;; it up to the empty line above the done items separator.
 	      (when (looking-back (concat "^"
 					  (regexp-quote todo-category-done)
 					  "\n")
@@ -2727,7 +2726,7 @@ meaning to raise or lower the item's priority by one."
 	       (let* ((ov (todo-get-overlay 'prefix))
 		      (pref (overlay-get ov 'before-string)))
 		 (overlay-put ov 'before-string
-			    (concat todo-item-mark pref))))))))
+			      (concat todo-item-mark pref)))))))))
 
 (defun todo-raise-item-priority ()
   "Raise priority of current item by moving it up by one item."
@@ -2768,8 +2767,7 @@ section in the category moved to."
                  (save-excursion (beginning-of-line)
                                  (looking-at todo-category-done)))
              (not marked))
-      (let* ((buffer-read-only)
-	     (file1 todo-current-todo-file)
+      (let* ((file1 todo-current-todo-file)
 	     (item (todo-item-string))
 	     (done-item (and (todo-done-item-p) item))
 	     (omark (save-excursion (todo-item-start) (point-marker)))
@@ -2828,7 +2826,8 @@ section in the category moved to."
                 (setq here (point))
                 (while todo-items
                   (todo-forward-item)
-                  (todo-insert-with-overlays (pop todo-items))))
+                  (let ((buffer-read-only nil))
+		    (todo-insert-with-overlays (pop todo-items)))))
 	      ;; Move done items en bloc to top of done items section.
               (when done-items
 		(todo-category-number cat2)
@@ -2842,7 +2841,8 @@ section in the category moved to."
 		(forward-line)
                 (unless here (setq here (point)))
                 (while done-items
-                  (todo-insert-with-overlays (pop done-items))
+                  (let ((buffer-read-only nil))
+		    (todo-insert-with-overlays (pop done-items)))
                   (todo-forward-item)))
               ;; If only done items were moved, move point to the top
               ;; one, otherwise, move point to the top moved todo item.
@@ -2881,12 +2881,14 @@ section in the category moved to."
 			(goto-char beg)
 			(while (< (point) end)
 			  (if (todo-marked-item-p)
-			      (todo-remove-item)
+			      (let ((buffer-read-only nil))
+				(todo-remove-item))
 			    (todo-forward-item)))
 			(setq todo-categories-with-marks
 			      (assq-delete-all cat1 todo-categories-with-marks)))
 		    (if ov (delete-overlay ov))
-		    (todo-remove-item))))
+		    (let ((buffer-read-only nil))
+		      (todo-remove-item)))))
 	      (when todo (todo-update-count 'todo (- todo) cat1))
 	      (when diary (todo-update-count 'diary (- diary) cat1))
 	      (when done (todo-update-count 'done (- done) cat1))
@@ -3015,8 +3017,7 @@ comments without asking."
 	 (marked (assoc cat todo-categories-with-marks))
 	 (num (if (not marked) 1 (cdr marked))))
     (when (or marked (todo-done-item-p))
-      (let ((buffer-read-only)
-	    (opoint (point))
+      (let ((opoint (point))
 	    (omark (point-marker))
 	    (first 'first)
 	    (item-count 0)
@@ -3078,6 +3079,7 @@ comments without asking."
 	  (when ov (delete-overlay ov))
 	  (if (not undone)
 	      (goto-char opoint)
+	    (let ((buffer-read-only nil))
 	      (if marked
 		  (progn
 		    (setq item nil)
@@ -3090,7 +3092,7 @@ comments without asking."
 		    (setq todo-categories-with-marks
 			  (assq-delete-all cat todo-categories-with-marks)))
 		(goto-char omark)
-	      (todo-remove-item))
+		(todo-remove-item)))
 	    (todo-update-count 'todo item-count)
 	    (todo-update-count 'done (- item-count))
 	    (when diary-count (todo-update-count 'diary diary-count))
@@ -3175,8 +3177,7 @@ this category does not exist in the archive, it is created."
 			  (concat (todo-item-string) "\n")))
 	       (count 0)
 	       (opoint (unless (todo-done-item-p) (point)))
-	       marked-items beg end all-done
-	       buffer-read-only)
+	       marked-items beg end all-done)
 	  (cond
 	   (all
 	    (if (todo-y-or-n-p "Archive all done items in this category? ")
@@ -3246,6 +3247,7 @@ this category does not exist in the archive, it is created."
 		  (todo-archive-mode))
                 (if headers-hidden (todo-toggle-item-header))))
 	    (with-current-buffer tbuf
+	      (let ((buffer-read-only nil))
 		(cond
 		 (all
 		  (save-excursion
@@ -3275,7 +3277,7 @@ this category does not exist in the archive, it is created."
 				 (todo-backward-item))
 			    (when item
 			      (throw 'done (setq item nil))))
-		      (todo-forward-item))))))
+			(todo-forward-item)))))))
 	      (when marked
 		(setq todo-categories-with-marks
 		      (assq-delete-all cat todo-categories-with-marks)))
@@ -3524,7 +3526,6 @@ decreasing or increasing its number."
       (let* ((maxnum (length todo-categories))
 	     (prompt (format "Set category priority (1-%d): " maxnum))
 	     (col (current-column))
-	     (buffer-read-only nil)
 	     (priority (cond ((and (eq arg 'raise) (> curnum 1))
 			      (1- curnum))
 			     ((and (eq arg 'lower) (< curnum maxnum))
@@ -3549,6 +3550,7 @@ decreasing or increasing its number."
 	       ;; Category's name and items counts list.
 	       (catcons (nth (1- curnum) todo-categories))
 	       (todo-categories (nconc head (list catcons) tail))
+	       (buffer-read-only nil)
 	       newcats)
 	  (when lower (setq todo-categories (nreverse todo-categories)))
 	  (setq todo-categories (delete-dups todo-categories))