type hints are missing in constructors when autodoc_typehints = 'description'

[xuhdev]

Describe the bug
Type hints are missing in constructors when autodoc_typehints = 'description'.

To Reproduce

1. Download bug.tar.gz and unarchive.
2. Run PYTHONPATH=. sphinx-build -d "./_build" docs "_build/html" -b html -W --color

├── docs
│   ├── conf.py
│   └── index.rst
└── myproject
    └── __init__.py

conf.py:

project = 'myproject'
copyright = '2020, someone'
author = 'someone'
autodoc_typehints = 'description'
extensions = [
    'sphinx.ext.autodoc',
]
html_theme = 'alabaster'

myproject/__init__.py:

class A:
    """
    :param boolean: I'm a boolean.
    """
    def __init__(self, boolean: bool):
        pass

index.rst is minimal:

Welcome to myproject's documentation!
=====================================

.. automodule:: myproject
   :members:
   :imported-members:

Expected behavior
Constructor parameter type hints should be documented.

Screenshots

With autodoc_typehints = 'description':

The type hint of bool should be in the description but it's missing.

Without autodoc_typehints = 'description', bool is shown on the function prototype line as expected:

Environment info

• OS: Debian 10
• Python version: 3.7.6
• Sphinx version: 3.4.3
• Sphinx extensions: autodoc

[tk0miya]

Thank you for reporting. This will be fixed by #8539.

[tk0miya]

Now #8539 is merged. It will be released as 4.0 soon.
Thanks,