Feature request: preserve source line numbers in AST nodes

[lvh]

Summary

It would be helpful if the parsed AST nodes included source line number information from the original markdown text.

Use case

When building linting tools that check markdown structure (e.g., heading hierarchy validation), error messages are much more useful when they can reference the specific line number:

Line 15: H1 not allowed in blog posts: 'Introduction'

vs just:

H1 not allowed in blog posts: 'Introduction'

Current behavior

The AST nodes only contain content, not source positions:

(require '[nextjournal.markdown :as md])
(md/parse "## Heading\n\nParagraph")
;; => {:content [{:type :heading, :heading-level 2, :content [...], :attrs {...}}
;;               {:type :paragraph, :content [...]}], ...}

Proposed behavior

Include source position information, perhaps as metadata or additional keys:

{:type :heading
 :heading-level 2
 :content [...]
 :attrs {...}
 :source {:line 1 :column 0}}  ;; or similar

Notes

The underlying commonmark-java parser does track source spans (SourceSpans), so this information is available during parsing but currently discarded.

[jackrusher]

+1. This would be a great improvement to the library.

[borkdude]

Seems good to me too.

The underlying commonmark-java parser does track source spans

Hopefully the underlying JS library does too. I can have a look at this in new year if nobody else beats me to it.