Builds fail when using MyST and autodoc with `docutils==0.17` installed

With docutils==0.17 (but not earlier), builds fail when using MyST alongside the autodoc extension, invoked via an eval-rst directive.

To reproduce, create this conf.py

import sys
sys.path.insert(0, '.')
extensions = ['myst_parser', 'sphinx.ext.autodoc']

this index.md

```{eval-rst}
.. automodule:: module
```

and this module.py

"""Lorem ipsum."""

Then run sphinx-build . output inside that folder. With docutils==0.16 installed, this renders as expected: A page that just says “Lorem ipsum.”

With docutils==0.17 (released a couple of days ago), I get this error:

Exception occurred:
  File "c:\programs\python\lib\site-packages\docutils\parsers\rst\__init__.py", line 196, in parse
    if len(line) > self.document.settings.line_length_limit:
AttributeError: 'Values' object has no attribute 'line_length_limit'

If I run the same build without the MyST parser, i.e. instead of index.md I have index.rst with .. automodule:: module in it, then things are fine again.

My environment is Sphinx 3.5.3, MyST 0.13.5, Python 3.9.2, Windows 10. But the same error occurs when Read-the-Docs builds my project on its server with sphinx>=2.0.0 required.

A similar issue with docutils==0.17 has been reported for recommonmark in readthedocs/recommonmark#220.

[chrisjsewell]

See #344

[chrisjsewell]

Hey yeh I have an idea of how to fix this. I’ve been side-tracked, messing around with some other stuff, but should be able to address this in the next day or two 👍