bpo-45192: Fix a bug that infers the type of an os.PathLike[bytes] object as str

[rekyungmin]

The tempfile module has been updated to accept an object implementing os.PathLike protocol for path-related parameters as of Python 3.6 (e.g. dir parameter). An os.PathLike object represents a filesystem path as a str or bytes object (i.e. def __fspath__(self) -> Union[str, bytes]:). However, if an object implementing os.PathLike[bytes] is passed as a dir argument, a TypeError is raised:

from typing import Union


class FakePath:
    def __init__(self, path):
        self.path = path

    def __fspath__(self) -> Union[str, bytes]:
        return self.path


if __name__ == "__main__":
    from tempfile import TemporaryDirectory

    # You need to create `existing_path` directory

    with TemporaryDirectory(dir=FakePath("existing_path")) as str_path:
        print(str_path)  # 'existing_path/...'

    with TemporaryDirectory(dir=FakePath(b"existing_path")) as byte_path:
        print(byte_path)  # expected b'existing_path/...' but raised TypeError

This bug occurs because the tempfile._infer_return_type function considers all non-bytes objects as str.

_infer_return_type function should infer os.PathLike[str] object as str type and os.PathLike[bytes] object as bytes type.

https://bugs.python.org/issue45192

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[rekyungmin]

I’m waiting for review.

[ambv]

Closing and re-opening to re-trigger CI.

[miss-islington]

Thanks @rekyungmin for the PR, and @ambv for merging it 🌮🎉.. I'm working now to backport this PR to: 3.9, 3.10.
🐍🍒⛏🤖

[bedevere-bot]

GH-29111 is a backport of this pull request to the 3.10 branch.

[bedevere-bot]

GH-29112 is a backport of this pull request to the 3.9 branch.