The **attrs** and **cattrs** packages version is incompatible.
Check command:
`pip check --use-feature=2020-resolver`

Code file: https://github.com/apache/airflow/blob/master/setup.py
Commit hash: 9150330
Line number:
694: 'attrs~=19.3'
696: 'cattrs~=1.0'

It will caused the final installed **attrs** version is higher than 20.1.0.

Why this happen?
From the dependency setting of **cattrs**:
https://github.com/Tinche/cattrs/blob/master/setup.py
Commit hash: 2f401b9
Line number:
12: "attrs >= 20.1.0"

setup.py
"""Set final values for options."""
    def run(self):  
        """List extras."""
        print("\n".join(wrap(", ".join(EXTRAS_REQUIREMENTS.keys()), 100)))
def git_version(version_: str) -> str:
    """
    Return a version to identify the state of the underlying git repo. The version will
    indicate whether the head of the current git-backed working directory is tied to a
    release tag or not : it will indicate the former with a 'release:{version}' prefix
    and the latter with a 'dev0' prefix. Following the prefix will be a sha of the current
    branch head. Finally, a "dirty" suffix is appended to indicate that uncommitted
    changes are present.
    :param str version_: Semver version
    :return: Found Airflow version in Git repo
    :rtype: str
    """
    try:
        import git
        try:
            repo = git.Repo(os.path.join(*[my_dir, '.git']))
        except git.NoSuchPathError:
            logger.warning('.git directory not found: Cannot compute the git version')
            return ''
        except git.InvalidGitRepositoryError:
            logger.warning('Invalid .git directory not found: Cannot compute the git version')
            return ''
    except ImportError:
        logger.warning('gitpython not found: Cannot compute the git version.')
        return ''
    if repo: