pip: PIP doesn't read setup.cfg in UTF-8, which causes UnicodeDecodeError

Environment

• pip version: 20.2.3
• Python version: 3.8.5
• OS: Win7x64

Description

When installing anything within a path that has a setup.cfg, pip will read it but fails at decoding if the file contains non-ASCII characters. The cfg file is proper UTF-8 but PIP doesn’t open it as so. It tries to use “GBK” (my locale) and fails.

Related, but not the same issue: #8717 (this is caused by pyvenv.cfg)

Expected behavior

It should read setup.cfg in UTF-8.

How to Reproduce

1. open a path.
2. Create a setup.cfg file with

[metadata]
name = test
version = 0.0.1
packages =
    test
description = '計算ツール'

1. Run pip install requests

Output

D:\test>pip install requests
ERROR: Exception:
Traceback (most recent call last):
  File "c:\program files\python3\lib\site-packages\pip\_internal\cli\base_command.py", line 228, in _main
    status = self.run(options, args)
  File "c:\program files\python3\lib\site-packages\pip\_internal\cli\req_command.py", line 182, in wrapper
    return func(self, options, args)
  File "c:\program files\python3\lib\site-packages\pip\_internal\commands\install.py", line 245, in run
    options.use_user_site = decide_user_install(
  File "c:\program files\python3\lib\site-packages\pip\_internal\commands\install.py", line 664, in decide_user_install
    if site_packages_writable(root=root_path, isolated=isolated_mode):
  File "c:\program files\python3\lib\site-packages\pip\_internal\commands\install.py", line 609, in site_packages_writab
le
    get_lib_location_guesses(root=root, isolated=isolated))
  File "c:\program files\python3\lib\site-packages\pip\_internal\commands\install.py", line 600, in get_lib_location_gue
sses
    scheme = distutils_scheme('', user=user, home=home, root=root,
  File "c:\program files\python3\lib\site-packages\pip\_internal\locations.py", line 109, in distutils_scheme
    d.parse_config_files()
  File "c:\program files\python3\lib\distutils\dist.py", line 406, in parse_config_files
    parser.read(filename)
  File "c:\program files\python3\lib\configparser.py", line 697, in read
    self._read(fp, filename)
  File "c:\program files\python3\lib\configparser.py", line 1017, in _read
    for lineno, line in enumerate(fp, start=1):
UnicodeDecodeError: 'gbk' codec can't decode byte 0xab in position 88: illegal multibyte sequence