`python-version-file` chooses most recent supported Python version, not the oldest supported version

[ErikBjare]

Description:

I'm using python-version-file: pyproject.toml to specify which Python version to use. My pyproject.toml is pretty standard poetry config, with a python = "^3.8" marker.

However, when using the action with such a config, it uses the most recent supported Python version. This doesn't make much sense to me, as Python code is generally forwards-compatible (except numpy/scipy/etc), but it is not backwards-compatible, as there are features in newer versions that aren't supported in previous versions (which is why I always run my CI jobs with the lowest supported Python minor version).

I expected it to pick the lowest supported minor version with the highest patch. Such that ^3.8 picks 3.8.15, not 3.12.0.

Justification:

With the current behavior, using python-version-file with a pyproject.toml that has a Python version marker specified with ^ (common) would basically be a no-op, as it will pick the same version as if python-version-file isn't specified at all.

Thus, I don't see much use for the current behavior, and would like to see it changed.

One option is to add a config to choose the behavior, which would prevent breakage in people's existing workflows. (as I did in #775)

Are you willing to submit a PR?

Yes! Done in #775

[dmitry-shibanov]

Hello @ErikBjare. Thank you for your feature request. It is an expected behaviour for caret symbol to pick the latest minor version. I think that the action should not directly interfer with python-version to change it somehow. You can use python-version input to specify different python versions as ~3.8 or 3.8 to get the proposed behaviour.

For now I'm going to close the feature request.

[ErikBjare]

@dmitry-shibanov Did you see my PR?

The current behavior really makes the python-version-file kinda worthless for use with Poetry pyproject.toml, for the reasons previously stated.

I'm aware I can just set the python-version like that, as that's what I've been doing, but I'd like to keep the Python version specified in a single place (as python-version-file enables).

I'd appreciate if you could give this a second consideration and reopen the issue, as this really surprised me and the current behavior is (imo) not usable.

It's a small and non-breaking change to adopt the additional configuration added in the PR.

[dmitry-shibanov]

It is an expected behaviour from the poetry side that they use caret notation. In this case poetry follows SemVer notation format that is why it is an expected behaviour to take the latest minor version. Caret and tilde are both valid variants for setup-python and poetry but they take different ranges. The action should not change the actual supported format from poetry through another input. You can try to use poetry env use <version> command, python-version input or change caret to tilde directly in the toml file.

[ErikBjare]

@dmitry-shibanov I am aware of all this, and I still feel you are misunderstanding my point here.

I guess I'll just use my own fork of the action.