[BUG] `setup-python` fails across multiple Windows and action versions when caching is requested and newer pip outputs a deprecation warning (any really)

[webknjaz]

UPD(17.02.2025): To anyone landing here from Google or hitting this bug otherwise

Tip

Here's the solution I landed on, not only because of just this bug, but I've also been wanting better cache control for quite a while, so I've wrapped what I've been copying and pasting for years into a more reusable component — a composite action that can sense whether it's safe to cache things based on the current runtime stability (ABI stability is computed based on the version being marked as final). Feel free to make use of it: https://github.com/re-actors/cache-python-deps.

The sample use would be

- name: Restore pip cache
  uses: re-actors/cache-python-deps@release/v1
  with:
    cache-key-for-dependency-files: >-
      ${{
        hashFiles(
          '.pre-commit-config.yaml',
          'requirements/**',
          'tox.ini',
          'tox.toml',
          'pyproject.toml'
        )
      }}

provided that it's invoked after setup-python and after a sort of checkout (or similar). Integration example: aio-libs/frozenlist#622 / aio-libs/frozenlist#633.

P.S. The root cause of the bug is that setup-python threads any stderr from pip as a failure in any Windows runtimes. New pip started outputting a warning about a CLI flag being deprecated. That CLI flag is often being set via env vars like PIP_NO_PYTHON_VERSION_WARNING (meant to suppress another warning in the output). More explanation here: #1034 (comment).

---

Description:

I've been updating a few GHA configurations today and in the process saw the same error in several places. Interestingly, in some repos it fails in one workflow but works in another. I've been seeing this for the past few hours, but this is in repos I haven't touched in months, so the issue might've appeared earlier.

I've tried finding differences and similarities, but cannot say anything definitive.

Among the similarities, there's these:

Current runner version: '2.322.0'
Runner Image
  Image: windows-2019
  Version: 20250209.1.0
Runner Image Provisioner
  2.0.422.1

Also, the action fails on both windows-2019 and windows-2022. It fails in matrixes that pass a variety of Python versions, starting with 3.9 and all the way to 3.13.

Another bit I noticed was that some of the jobs downloaded immutable actions, while others fetched from Git. But there's examples of both in failing/passing action invocations.

Failing job examples (there's more in the same workflow runs):

• https://github.com/aio-libs/frozenlist/actions/runs/13314999958/job/37186948056#step:4:27
• https://github.com/cherrypy/cheroot/actions/runs/13314563336/job/37185295001#step:3:20

Success example:

• https://github.com/cherrypy/cheroot/actions/runs/13314453736/job/37185039139#step:2:27

As you can see, there's successes and failures in the same repo, just different job definitions.

While writing this, I also noticed that the failing ones have some sort of file preparation before calling setup-python and caching args enabled. Worth checking out... I'll report back once I experiment some more.

Action version:

v5

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Tools version:

🤷‍♂ seems to be any Python version and any windows image.

Repro steps:

Add a step with actions/setup-python@v5 into a windows job, set PIP_NO_PYTHON_VERSION_WARNING: 1 env var and add the cache: pip input.

Expected behavior:

It should succeed.

Actual behavior:

The action spits out Error: Could not get cache folder path for pip package manager, after the successful Installed versions output, and crashes the job.

[webknjaz]

So this experiment shows that dropping the cache inputs makes it pass: aio-libs/frozenlist#622.

[suyashgaonkar]

Hi @webknjaz ,Thank you for creating this issue. We will investigate it and provide feedback as soon as we have some updates.

[webknjaz]

This is the line that the action hits in the broken scenario:

setup-python/src/cache-distributions/pip-cache.ts

Line 46 in 8039c45

`Could not get cache folder path for pip package manager`

.

I tried various things so far.

Moving the requirements files mentioned in the cache-dependency-path to the top level of the repo does not help: https://github.com/aio-libs/frozenlist/actions/runs/13328642529/job/37227633874?pr=627#step:4:27. This excludes the possibility of this problem being related to non-normalized path separator (slash vs. backslash).

Moving setup-python before checkout makes it break due to the absence of the req files. This is expected.

Deleting the cache and cache-dependency-path inputs does work. So it's a viable workaround. https://github.com/aio-libs/frozenlist/actions/runs/13315768115/job/37189473317?pr=622#step:4:23