autodoc does not recognize Cython property as such

Because of implementation details, @property of Cython extension types are not the same as created by the builtin property function. For this reason, autodoc doesn't seem to be able to recognize these descriptor as such.

To Reproduce

First create a sample Cython module with the mentioned elements:

getter = property   # bypass Cython property hijack
setter = lambda fset: property(fset=fset, doc=fset.__doc__)     # noqa


cdef class Spam:
    @property
    def foo(self) -> int: return 42

    @getter
    def bar(self) -> float: return 6.9

    @setter
    def baz(self, value: bool) -> None: pass

as well as a setup.py for compilation

from distutils.core import setup
from Cython.Build import cythonize

setup(name='autospam',
      ext_modules=cythonize('cyspam.pyx',
                            compiler_directives={'binding': True}))

Use pip install . to install and cyspam should be importable.

Now if we create a sample project with the following content (I was a bit lazy to think of the documentations for the properties):

.. autoclass:: cyspam.Spam
   :undoc-members:

the rendered HTML looks like this:

Expected behavior

It is expected that foo shows up as a property as well.

Sample project

autospam.zip

Environment info

• OS: [e.g. Unix/Linux/Mac/Win/other with version]
• Python version: 3.7.7
• Sphinx version: 3.0.0
• Sphinx extensions: sphinx.ext.autodoc
• Extra tools: Cython

Start at the sphinx.ext.autodoc entry point and reproduce the behavior with cyspam.pyx, setup.py, and the sample autoclass directive. Check the rendered output for Spam; done means the Cython foo descriptor is recognized and presented as a property alongside the other descriptors.