AttributeError when using X | Y type hinting syntax with sphinx.ext.autodoc

[adamtheturtle]

Describe the bug

Using type syntax like name: str | int is now supported in Python (with an import from __future__) but autodoc-ing a class which uses this syntax produces an AttributeError.

To Reproduce

I have the following sample project:

Python 3.9.1

.
├── docs
│   └── source
│       ├── conf.py
│       └── index.rst
└── example_module.py

docs/source/conf.py:

import os
import sys

sys.path.insert(0, os.path.abspath('../..'))
extensions = ['sphinx.ext.autodoc']

docs/source/index.rst:

.. autoclass:: example_module.Foo
   :members:
   :undoc-members:

example_module.py:

from __future__ import annotations

class Foo:
    # See http://mypy-lang.blogspot.com/2021/01/mypy-0800-released.html
    # for a description of this syntax.
    name: str | int

Command:

sphinx-build -b html docs/source/ docs/build

Expected behavior

No error.
Sphinx builds documentation which makes it clear that name can be an int or a str.

Environment info

• OS: macOS 11.1
• Python version: 3.9.1
• Sphinx version: 3.4.3
• Sphinx extensions: sphinx.ext.autodoc

[tk0miya]

autodoc uses python interpreter itself to recognize type hints. So you need to run Sphinx under python 3.10 to recognize union types operator.

[adamtheturtle]

@tk0miya Thank you for your response. This is a topic I'm not super familiar with but my hope was that as the type checking works under 3.9.1 (given the __future__ import), so would autodoc.

[tk0miya]

No, it is not related to your python interpreter. mypy-0.800 supports the new Union syntax, not python itself. So it will also work when you're using new mypy even with python-3.8. autodoc can support the syntax if somebody sends us a patch!

[adamtheturtle]

Great, and thanks for the work I can see already on this from you @tk0miya . Your work on this project is a gift 🙏

[tk0miya]

Now I posted #8805 to avoid the crash by union types operator. But it does not mean Sphinx supports it with Python 3.9 or below. I think it is a workaround because it disables autodoc_type_alises feature when the error is raised internally. I don't know it's really worthy. But it would work well for some people. Thanks,