Python 3.9 + Windows: Does not handle long paths like other versions

[pradyunsg]

Description:
Python 3.9 seems to behave differently from other Python versions, when handling long paths on Windows. This looks suspiciously like non-LongPathAware behaviour.

Action version:
Specify the action version: v2?

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Tools version:

3.9

Repro steps:
A description with steps to reproduce the issue. If your have a public example or repo to share, please provide the link.

name: Release
on:
  push:

jobs:
  windows:
    name: ${{ matrix.python }} / ${{ matrix.os }}
    strategy:
      matrix:
        os: [Windows]
        python:
          - 3.7
          - 3.8
          - 3.9
          - "3.10"

    runs-on: ${{ matrix.os }}-latest
    steps:
      - uses: actions/setup-python@v2
        with:
          python-version: ${{ matrix.python }}

      - run: python -c "from pathlib import Path; (Path.cwd() / ('a'*131) / ('a'*131)).mkdir(parents=True)"

• https://github.com/pradyunsg/testing-grounds/actions/runs/1452413343 for the run output/behaviour.
• https://github.com/pradyunsg/testing-grounds/tree/c409e864e107f9cfead32d440a569e96144fda0a for the GitHub actions configuration.

Noticed since this was causing errors in pip's test suite: https://github.com/pypa/pip/runs/4187290412?check_suite_focus=true

Expected behavior:
Python 3.9 behaves like other Python versions, and handles long paths on Windows.

Actual behavior:
Python 3.9 fails when handling long paths on Windows.

[pradyunsg]

Oh, and this seems to be a somewhat-recent change, since pip had the same-ish setup working 5 days ago: https://github.com/pypa/pip/runs/4130255296?check_suite_focus=true

[layday]

This is related to the upgrade to 3.9.8 which is the first Python version to have been released with python/cpython@06935bd. The same warning/failure will appear in Python 3.10 next month.

Also experiencing this at pypa/build.

[layday]

Okay, that actually appears to be a manifestation of the issue with paths - I didn't look close enough, sorry.

[uranusjr]

Make pipx the third PyPA project being affected 🙂

[nikita-bykov]

Hello @pradyunsg! We were be able to reproduce this issue on windows-latest hosted image, but it also reproduces on the local Windows machine. It looks like the issue is not related to setup-python action, but to Python 3.9.8.
As a workaround, you can install Python 3.9.9 using setup-python action. Also next week this Python version will be available in GitHub hosted images and version 3.9 will point to 3.9.9.

[uranusjr]

What steps are needed to reproduce this locally? I don’t recall 3.9.9 containing a fix for this, so we may want to report this to upstream CPython so they can investigate properly. Even if the bug is fixed in 3.9.9, the fact that it manifests but disappears on its own is enough reason for it to be more thoroughly investigated.

[nikita-bykov]

Hello @uranusjr, I installed Python 3.9.8 on my Windows machine using choco and executed the following command from repro steps:

python -c "from pathlib import Path; (Path.cwd() / ('a'*131) / ('a'*131)).mkdir(parents=True)"

I got the same error as in https://github.com/pradyunsg/testing-grounds/runs/4187901999?check_suite_focus=true

[uranusjr]

I tracked this down: https://bugs.python.org/issue45777

So yes, 3.9.8 is the only broken release, it’s built with faulty configuration. The solution is to use 3.9.9 (or anything but 3.9.8).

[layday]

So this is supposed to be fixed in 3.9.9? Because 3.9.9 is failing for pypa/build on Windows.

[uranusjr]

Yes, the 3.9.9 build of CPython is supposed to work (if you have LongPathsEnabled set correctly system-wide, of course; that is always a prerequisite).

[nikita-bykov]

@layday I'm going to close the issue because it related to Python 3.9.8 and not to setup-python.
If you have any questions feel free to contact us.