Documents with no level-1 heading subsume all level-2 headings under the first level-2 heading

[DivineDominion]

Sample document

---
title: Wat
---
## Section a

### Sub 1

### Sub 11

## Section b

### Sub 2

The imenu output of counsel-imenu and also the outline in treemacs shows this hierarchy:

I expected Section b and Section a to be siblings, but Section b is demoted to a child of Section a.

The code that is responsible for this is likely this parser:

markdown-mode/markdown-mode.el

Lines 5532 to 5587 in 4d7f525

	(defun markdown-imenu-create-nested-index ()
	"Create and return a nested imenu index alist for the current buffer.
	See `imenu-create-index-function' and `imenu--index-alist' for details."
	(let* ((root '(nil . nil))
	cur-alist
	(cur-level 0)
	(empty-heading "-")
	(self-heading ".")
	hashes pos level heading)
	(save-excursion
	;; Headings
	(goto-char (point-min))
	(while (re-search-forward markdown-regex-header (point-max) t)
	(unless (markdown-code-block-at-point-p)
	(cond
	((match-string-no-properties 2) ;; level 1 setext
	(setq heading (match-string-no-properties 1))
	(setq pos (match-beginning 1)
	level 1))
	((match-string-no-properties 3) ;; level 2 setext
	(setq heading (match-string-no-properties 1))
	(setq pos (match-beginning 1)
	level 2))
	((setq hashes (markdown-trim-whitespace
	(match-string-no-properties 4)))
	(setq heading (match-string-no-properties 5)
	pos (match-beginning 4)
	level (length hashes))))
	(let ((alist (list (cons heading pos))))
	(cond
	((= cur-level level) ; new sibling
	(setcdr cur-alist alist)
	(setq cur-alist alist))
	((< cur-level level) ; first child
	(dotimes (_ (- level cur-level 1))
	(setq alist (list (cons empty-heading alist))))
	(if cur-alist
	(let* ((parent (car cur-alist))
	(self-pos (cdr parent)))
	(setcdr parent (cons (cons self-heading self-pos) alist)))
	(setcdr root alist)) ; primogenitor
	(setq cur-alist alist)
	(setq cur-level level))
	(t ; new sibling of an ancestor
	(let ((sibling-alist (last (cdr root))))
	(dotimes (_ (1- level))
	(setq sibling-alist (last (cdar sibling-alist))))
	(setcdr sibling-alist alist)
	(setq cur-alist alist))
	(setq cur-level level))))))
	;; Footnotes
	(let ((fn (markdown-get-defined-footnotes)))
	(if (or (zerop (length fn))
	(null markdown-add-footnotes-to-imenu))
	(cdr root)
	(nconc (cdr root) (list (cons "Footnotes" fn))))))))

I may or may not be able to adjust this myself, we'll see, as my elisp isn't that good :) So I'm posting this issue to track the behavior. If someone else chimes in, great!.

[DivineDominion]

If all headings are level-2 headings, the nested display won't occur. In the parser, level-1 and level-2 are handled separately.

So the level-3 match starting at line 5555 affects the result.

[syohex]

It looks markdown imenu function assumes there is at least one level1 header when there is a level2 header. I suppose the imenu function should be re-written.

[syohex]

@DivineDominion I have merged #574. Please check latest version

[DivineDominion]

That was super quick and helpful, thank you a thousandfold @syohex! 🎉