Parse line numbers

Is it possible to retrieve information about the line number of block-level elements in the AST? We are looking into using Mistune for a project and this would be quite helpful.

E.g., running:

markdown = mistune.create_markdown(renderer=mistune.AstRenderer())
markdown("# Heading 1\n\n## Heading2")

to return something like

[{'type': 'heading',
  'children': [{'type': 'text', 'text': 'Heading 1'}],
  'level': 1,
  'lineno': 0},
 {'type': 'heading',
  'children': [{'type': 'text', 'text': 'Heading2'}],
  'level': 2,
  'lineno': 2}]

If it’s not possible currently, is it something that would be doable w/ a PR?

[waylan]

What is the usage of line numbers in your case?

I would be using this for a linter like tool. Perhaps a spellchecker or a link checker. In the care of a spellchecker, the tool should skip anything within code blocks or spans, so we can’t just pass the entire document into a spellchecker. In the case of a link checker, we need to find all links (external, internal, absolute, relative). In each case, the easiest way to ensure we are checking the correct content is by running the document through a Markdown parser.

Of course, we could pass the rendered HTML into any number of existing tools, but that will present any errors found with the location in the HTML. However, ideally, the location (line and column) in the Markdown source document would be preferred. That way the user can easily find the error and fix it.

To implement such a tool, I would create my own custom renderer which would step through the AST, checking the content of the various nodes. For any nodes without errors, the renderer would return nothing. However, when an error is encountered, the renderer would report the error, ideally with the line and column.

See the oversimplified pseudo example of a link checker below

class LinkChecker(BaseRenderer):
    NAME = 'linkchecker'
    IS_TREE = False

    def text(self, text):
        return ''

    def link(self, link, pos, children=None, title=None):
        result = validate(link):
        if result:
            return f'ERROR at {pos.line}:{pos.col} {link} --> {result.code}\n'
         return ''

[ddevault]

Tracking line numbers would definitely not make mistune slower unless the feature was egregiously poorly implemented.