Sphinx 4.3 fails when importing PyQt5.QtCore.pyqtSignal

[bicobus]

Describe the bug

With Sphinx 4.3, usage of pyqtSignal will fail with the following error:

  File ".../lib/python3.8/site-packages/sphinx/util/docstrings.py", line 75, in prepare_docstring
    lines = s.expandtabs(tabsize).splitlines()
AttributeError: 'getset_descriptor' object has no attribute 'expandtabs'

Using exact same codebase, Sphinx 4.2 doesn't have such issue.

Investigating why, I stumbled upon the following:

> .../lib/python3.8/site-packages/sphinx/util/docstrings.py(75)prepare_docstring()
-> lines = s.expandtabs(tabsize).splitlines()
(Pdb) l
 70  	        ignore = 1
 71  	    else:
 72  	        warnings.warn("The 'ignore' argument to prepare_docstring() is deprecated.",
 73  	                      RemovedInSphinx50Warning, stacklevel=2)
 74  	
 75  ->	    lines = s.expandtabs(tabsize).splitlines()
 76  	    # Find minimum indentation of any non-blank lines after ignored lines.
 77  	    margin = sys.maxsize
 78  	    for line in lines[ignore:]:
 79  	        content = len(line.lstrip())
 80  	        if content:
(Pdb) interact
*interactive*
>>> s
<attribute '__doc__' of 'PyQt5.QtCore.pyqtSignal' objects>
>>> dir(s)
['__class__', '__delattr__', '__delete__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__get__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__name__', '__ne__', '__new__', '__objclass__', '__qualname__', '__reduce__', '__reduce_ex__', '__repr__', '__set__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__']
>>> 
now exiting InteractiveConsole...
(Pdb) 
make: *** [Makefile:19: html] Error 2

Removing references to pyqtSignal allows sphinx to successfully compile the documentation.

How to Reproduce

Assuming you can quickstart the sphinxdocs folder yourself, insert the following snippet into a file and run sphinx against it.

from PyQt5.QtCore import pyqtSignal

class test:
    """test"""
    x = pyqtSignal([tuple])

Don't forget to install PyQt5:

$ pip install PyQt5

Expected behavior

No response

Your project

Please follow reproduction steps.

Screenshots

No response

OS

Linux

Python version

3.8

Sphinx version

4.3.0

Sphinx extensions

No response

Extra tools

No response

Additional context

No response

[tk0miya]

Thank you for reporting.

>>> s
<attribute '__doc__' of 'PyQt5.QtCore.pyqtSignal' objects>

Hmm... I feel this pyqtSignal is broken because it returns non-string object as __doc__...