pip install --upgrade pip on v22.0 broken on windows

[banesullivan]

Description

pip install --upgrade pip is failing on windows GitHub actions runners with v22.0

See pyvista/pyvista#2113

See example workflow shared below

See https://github.com/pyvista/pyvista/runs/4998090770?check_suite_focus=true#step:4:1

Expected behavior

Pip should be able to upgrade itself on windows for Python 3.7 and greater

pip version

22.0

Python version

3.7+

OS

Windows

How to Reproduce

Use this GitHub Actions workflow:

name: Unit Testing

on:

jobs:
  windows:
    name: Windows Unit Testing
    runs-on: windows-2019
    strategy:
      fail-fast: false
      matrix:
        python-version: [3.6, 3.7, 3.8, 3.9]
    steps:
      - name: Set up Python
        uses: actions/setup-python@v2
        with:
          python-version: ${{ matrix.python-version }}

      - name: Upgrade pip
        run: pip install --upgrade pip

Output

pip install --upgrade pip
  pip install --upgrade pip
  shell: C:\Program Files\PowerShell\7\pwsh.EXE -command ". '{0}'"
  env:
    ALLOW_PLOTTING: true
    SHELLOPTS: errexit:pipefail
    CI_WINDOWS: true
    pythonLocation: C:\hostedtoolcache\windows\Python\3.7.9\x64
Requirement already satisfied: pip in c:\hostedtoolcache\windows\python\3.7.9\x64\lib\site-packages (21.3.1)
Collecting pip
  Downloading pip-22.0-py3-none-any.whl (2.1 MB)
Installing collected packages: pip
  Attempting uninstall: pip
    Found existing installation: pip 21.3.1
    Uninstalling pip-21.3.1:
      Successfully uninstalled pip-21.3.1
ERROR: Could not install packages due to an OSError: [WinError 5] Access is denied: 'C:\\Users\\RUNNER~1\\AppData\\Local\\Temp\\pip-uninstall-2ea7t7u5\\pip.exe'
Consider using the `--user` option or check the permissions.

Error: Process completed with exit code 1.

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[pradyunsg]

You'll want to run python -m pip ... for that. I'm not sure why pip's detection logic is broken on Windows, since we'd added a dedicated warning to detect this situation.

[banesullivan]

Thanks for the tip!!

Also, I want to make sure it's clear in my issue that this broke on v22 but works fine on v21

[RoDuth]

Noticed something very similar today on MinGW x64. This had also worked until upgrading from v21 to v22.

$ pip install --upgrade pip
Requirement already satisfied: pip in c:/msys64/mingw64/lib/python3.9/site-packages (21.3.1)
Collecting pip
  Downloading pip-22.0.2-py3-none-any.whl (2.1 MB)
     |################################| 2.1 MB 3.3 MB/s
Installing collected packages: pip
  Attempting uninstall: pip
    Found existing installation: pip 21.3.1
    Uninstalling pip-21.3.1:
      Successfully uninstalled pip-21.3.1
ERROR: Could not install packages due to an OSError: [WinError 5] Access is denied: 'C:/Users/test/AppData/Local/Temp/pip-uninstall-bau5mi39\\pip.exe'
Consider using the `--user` option or check the permissions.

seems the path C:/Users/test/AppData/Local/Temp/pip-uninstall-bau5mi39\\pip.exe is mangled, mixing Windows and POSIX path separators