org-list: Change behaviour of C-c C-c at a list item with an argument

* lisp/org-list.el (org-list-write-struct): Add an optional argument
  for structure changes happening outside the function.
* lisp/org.el (org-ctrl-c-ctrl-c): Now, C-u C-c C-c on the first item
  of a sub-list should toggle check-box presence of every item in the
  same sub-list.  Also fix check-box insertion on a single item.

lisp/org-list.el

@@ -1914,16 +1914,21 @@ Initial position of cursor is restored after the changes."
     (goto-char origin)
     (move-marker origin nil)))
 
-(defun org-list-write-struct (struct parents)
+(defun org-list-write-struct (struct parents &optional old-struct)
   "Correct bullets, checkboxes and indentation in list at point.
+
 STRUCT is the list structure.  PARENTS is the alist of parents,
-as returned by `org-list-parents-alist'."
+as returned by `org-list-parents-alist'.
+
+When non-nil, optional argument OLD-STRUCT is the reference
+structure of the list.  It should be provided whenever STRUCT
+doesn't correspond anymore to the real list in buffer."
   ;; Order of functions matters here: checkboxes and endings need
   ;; correct indentation to be set, and indentation needs correct
   ;; bullets.
   ;;
   ;; 0. Save a copy of structure before modifications
-  (let ((old-struct (copy-tree struct)))
+  (let ((old-struct (or old-struct (copy-tree struct))))
     ;; 1. Set a temporary, but coherent with PARENTS, indentation in
     ;;    order to get items endings and bullets properly
     (org-list-struct-fix-ind struct parents 2)

lisp/org.el

@@ -18390,12 +18390,19 @@ This command does many different things, depending on context:
 	     block-item)
 	;; Use a light version of `org-toggle-checkbox' to avoid
 	;; computing list structure twice.
-	(org-list-set-checkbox (point-at-bol) struct
-			       (cond
-				((equal arg '(16)) "[-]")
-				((equal arg '(4)) nil)
-				((equal "[X]" cbox) "[ ]")
-				(t "[X]")))
+	(let ((new-box (cond
+			((equal arg '(16)) "[-]")
+			((equal arg '(4)) nil)
+			((equal "[X]" cbox) "[ ]")
+			(t "[X]"))))
+	  (if firstp
+	      ;; If at first item of sub-list, remove check-box from
+	      ;; every item at the same level.
+	      (mapc
+	       (lambda (pos) (org-list-set-checkbox pos struct new-box))
+	       (org-list-get-all-items
+		(point-at-bol) struct (org-list-prevs-alist struct)))
+	    (org-list-set-checkbox (point-at-bol) struct new-box)))
 	;; Replicate `org-list-write-struct', while grabbing a return
 	;; value from `org-list-struct-fix-box'.
 	(org-list-struct-fix-ind struct parents 2)
@@ -18417,9 +18424,20 @@ This command does many different things, depending on context:
       ;; only if function was called with an argument.  Send list only
       ;; if at top item.
       (let* ((struct (org-list-struct))
+	     (new-struct struct)
 	     (firstp (= (org-list-get-top-point struct) (point-at-bol))))
-	(when arg (org-list-set-checkbox (point-at-bol) struct "[ ]"))
-	(org-list-write-struct struct (org-list-parents-alist struct))
+	(when arg
+	  (setq new-struct (copy-tree struct))
+	  (if firstp
+	      ;; If at first item of sub-list, add check-box to every
+	      ;; item at the same level.
+	      (mapc
+	       (lambda (pos) (org-list-set-checkbox pos new-struct "[ ]"))
+	       (org-list-get-all-items
+		(point-at-bol) new-struct (org-list-prevs-alist new-struct)))
+	    (org-list-set-checkbox (point-at-bol) new-struct "[ ]")))
+	(org-list-write-struct
+	 new-struct (org-list-parents-alist new-struct) struct)
 	(when arg (org-update-checkbox-count-maybe))
 	(when firstp (org-list-send-list 'maybe))))
      ((save-excursion (beginning-of-line 1) (looking-at org-dblock-start-re))