PEP 604 Syntax Fails on Imported Types with Automock Imports

[intermezzio]

Describe the bug

Sphinx raises an error when an imported type is joined with another type via the pipe operator in a type hint even though it is valid syntax for PEP 604.

How to Reproduce

import numpy as np

def func_1(inp: np.ndarray | None):
    pass # should work but doesn't

def func_2(inp: type(np.array([])) | None):
    pass # works but is cursed

def func_3(inp: np.ndarray):
    pass # works fine

def func_4(inp: list | None):
    pass # works fine

conf.py contains the following:

autodoc_mock_imports = ["numpy"]

Environment Information

Platform:              linux; (Linux-5.15.93-1-MANJARO-x86_64-with-glibc2.37)
Python version:        3.10.9 (main, Dec 19 2022, 17:35:49) [GCC 12.2.0])
Python implementation: CPython
Sphinx version:        6.1.3
Docutils version:      0.18.1
Jinja2 version:        3.1.2
Pygments version:      2.14.0

Sphinx extensions

["sphinx.ext.autodoc"]

Additional context

No response

[asaril]

I think I just ran into the same issue when using an imported type from a mocked module in a PEP604 Union. (Similar versions, sphinx 6.1.3, python 3.10.12)

[edit] retried it with sphinx 7.2.5, same behavior (ext.autodoc.mock.py is mostly unchanged, so that was expected [/edit]

The mock factory creates a new type() in the mock module's getattr, and returns an instance of that.
The instance in itself is not a type, so it does not gain the | operator for types.

(also, calling & or | on the mock objects with any other value/object seems to not work).

If the mock is only used in a type-checking context, it could be worked around by either returning the type itself, or implementing a __or__(__value) method in _MockObject, that can return a typing.Union[self, __value].
Both of these could potentially break imports where it should have been a value/instance instead.