Passing a class to a decorator factory now fails to import for mocked decorators

[andyneff]

Describe the bug

It looks like while #6719 added support for decorators from mocked modules.

Unfortunately, when you using a decorator factory, (a function that returns a decorator or a decorator that takes arguments), if a class is an argument to the decorator factory, it attempts to instantiate the class, and fails to import the file.

To Reproduce

Example:

import mocked_module

class SomeClass:
  def __init__(self): # If this init takes two arguments, it won't "fail", but is still technically wrong
    pass

@mocked_module.decorator2(SomeClass)
class MyClass:
  ''' This is a class '''
  pass

Somehow mocked_module.decorator2 appears to be calling SomeClass's __init__ with two arguments

Error when building docs:

WARNING: autodoc: failed to import module 'bar' from module 'foo'; the following exception was raised:
Traceback (most recent call last):
  File "/home/andy/.local/share/virtualenvs/sphinx_decorator_bug-0V71t1Ku/lib/python3.7/site-packages/sphinx/ext/autodoc/importer.py", line 66, in import_module
    return importlib.import_module(modname)
  File "/home/andy/.local/share/virtualenvs/sphinx_decorator_bug-0V71t1Ku/lib64/python3.7/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1006, in _gcd_import
  File "<frozen importlib._bootstrap>", line 983, in _find_and_load
  File "<frozen importlib._bootstrap>", line 967, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 677, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 728, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/opt/projects/sphinx_decorator_bug/foo/bar.py", line 29, in <module>
    @mocked_module.decorator2(BaseClass)
TypeError: __init__() takes 1 positional argument but 2 were given

Expected behavior

At the very least, it should not be trying to instantiate SomeClass at all and it should not fail to import. Ideally, it would work and document MyClass, the decorated class.

Work around

Not mocking the particular class works. If I added the third party library to the sphinx environment, and use it directly instead of mocking, it seems to work.

Your project

https://github.com/andyneff/sphinx_decorator_bug

Environment info

• OS: Fedora 31
• Python version: 3.7.8
• Sphinx version: 2.3.0 - 3.2.1
• Sphinx extensions: [sphinx.ext.autodoc, sphinx.ext.napoleon]
• Also reproduced in the python:3.7.0 docker image