Install fails: regression in v4 compared do v3

[adrinjalali]

Description:
We noticed a while ago that some of our actions are failing due to failing import statements. After investigating, @BenjaminBossan managed to have a minimal reproducible which you can see here: BenjaminBossan/mops#10

Somehow pip install . doesn't properly install the package in site-packages with v4, while it does with v3. The PR linked above shows two actions, the difference being the version of setup-python, one passing the other one failing.

Action version:
v4

Platform:

• Ubuntu
• macOS
• Windows

Runner type:

• Hosted
• Self-hosted

Tools version:

Repro steps:
Explained here: BenjaminBossan/mops#10

Expected behavior:
Package should be installed properly.

Actual behavior:
Files are missing from the installation folder.

[e-korolevskii]

Hello @adrinjalali
Thank you for your report. We'll investigate the issue and get back to you.

[dmitry-shibanov]

Hello @adrinjalali. Thank you for your report. I think it's an expected behaviour because previously if python-version is empty the action will set it to 3.x. For setup-python@v4 it will try to find .python-version and if it is not found it will use default python on the machine. Could you please try to specify python-version: 3.x ?

[adrinjalali]

Thanks for the quick response. That kinda fix the issue, but only if we set the python version to >=3.10. It fails with <=3.9.

Tested in the same PR: BenjaminBossan/mops#10, the last 4 runs show the difference.

[dmitry-shibanov]

Hello @adrinjalali. For now I'm going to close the issue because it was an expected change made in v4.

[adrinjalali]

@dmitry-shibanov is the expected behavior that we can't install the package correctly in older python versions?

If you have a look at the last 4 commits here (BenjaminBossan/mops#10) you see that this issue is not fixed, and I don't think the expected behavior is that it fails for older python versions.