Running org-ml-update on item changes its nesting level

[eagerchatterjee]

Running org-ml-update on an item changes its "level" by collapsing two plain lists into one.

Minimal Example

Original Contents

* Headline
- [ ] foo
  - [ ] bar

Code Run

(->> (org-ml-parse-this-headline)
  (org-ml-match '(:last :any * item))
  car
  (org-ml-update #'identity))

Actual Result

* Headline
- [ ] foo
- [ ] bar

Expected Result

* Headline
- [ ] foo
  - [ ] bar

[eagerchatterjee]

Updating an item alone can change its indentation because list indentation is contextual, not an independent item property. org-ml is likely reserializing the item in a normalized way without enough plain-list context, so sibling and nesting indentation gets rewritten.

A fix is to update the item through its top-level plain-list parent rather than rewriting the item node directly:

1. find the target item
2. get its top-level plain-list ancestor
3. find the item's index in that plain-list, e.g. by matching its :begin
4. update that indexed item inside the plain-list
5. write back the whole plain-list

Example of Approach That Works

(defun my-get-top-level-parent-of-type (type node)
  (->> node
       org-ml-get-parents
       (--first (eq type (org-ml-get-type it)))))

(defun my-get-index-of-item-within-list (item plain-list)
  (org-ml--check-type 'item item)
  (org-ml--check-type 'plain-list plain-list)
  (let* ((item-begin (org-ml-get-property :begin item))
         (items (org-ml-match '(:any * item) plain-list)))
    (-find-index
     (lambda (candidate)
       (= item-begin (org-ml-get-property :begin candidate)))
     items)))

;; here we just pick an item at random which is in a nested plain-list
(let* ((headline (org-ml-parse-this-headline))
       (item (->> headline (org-ml-match '(:any * item)) (nth 2)))
       (plain-list (my-get-top-level-parent-of-type 'plain-list item))
       (index (my-get-index-of-item-within-list item plain-list)))
  (->> plain-list
       (org-ml-update*
        (org-ml-match-map* `(:nth ,index :any * item)
          (org-ml-set-property :counter 12 it)
          it))))