sphinx.ext.autosectionlabel and myst_parser not compatible

[torbsorb]

Describe the bug

context When I use sphinx.ext.autosectionlabel and myst_parser for an rst project it triggers an exception:

See also https://github.com/sphinx-doc/sphinx/issues/10902.

sphinx.ext.autosectionlabel configuration:

autosectionlabel_prefix_document = True
autosectionlabel_maxdepth = 2

expectation I expected no exceptions to be raised.

bug

Extension error (sphinx.ext.autosectionlabel):
Handler <function register_sections_as_label at 0x7fcf255cf910> for event 'doctree-read' threw an exception (exception: 'NoneType' object has no attribute 'parent')

problem When sphinx.ext.autosectionlabel is trying to find node depth it looks for cur_node.parent == node.document. However, with myst_parser the parent node of the document where this is included is not the parent. Instead the top-level parent is set to None. This is what triggers the exception. If the plan was to have None as the top-level parent, then https://github.com/sphinx-doc/sphinx/issues/10902 must be fixed. However, I believe myst_parser should attempt to set parent node to the document where the markdown is included.

Reproduce the bug

Enable sphinx.ext.autosectionlabel and use myst_parser

.. include:: a_markdown_file.md
   :parser: myst_parser.sphinx_

List your environment

Ubuntu 20.04 in WSL2 on Windows 11 Python 3.10.6 docutils 0.17.1 myst_parser 0.18.0

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[jhj0411jhj]

I also encountered this bug when autosectionlabel_maxdepth is not None, and I write the 'including markdown file in rst file' syntax:

.. include:: ../../../CHANGELOG.md
   :parser: myst_parser.sphinx_

When the parser is parsing this rst file, the error raises.

To avoid it, I set autosectionlabel_maxdepth=None. Or remove the include syntax.