Describe the bug
When testing large projects it is convenient to cache dependencies from pypi with a cache key based on the projects setup.py. I've been been using that pattern (yaml shown below) on several projects for > 6 months. It works great, but periodically (every 1-6 weeks) fails with the error:

Once the error occurs once, it will appear consistently until I alter the cache key and force the virtual environment to rebuild.

I think what's happening is that every time the build/setup for the setup-python action changes, it invalidates the link between the virtual environment and the python binary.

Questions:

• Is there a recommended method for caching dependencies with setup-python that will not suffer from this issue
• Could you recommend file/something that can be hashed and added to the cache key to invalidate the cache when new python builds are pushed?

    steps:

    - name: set up python 3.8
      uses: actions/setup-python@v1
      with:
        python-version: 3.8

    - name: checkout
      uses: actions/checkout@v2

    - name: cache dependencies
      id: xyz-cache
      uses: actions/cache@v2
      with:
        path: venv
        key: ${{ runner.os }}-pip-${{ hashFiles('setup.py') }}-0

    - name: install xyz
      if: steps.sl-cache.outputs.cache-hit != 'true'
      run: |
        python -m venv venv
        source venv/bin/activate
        python -m pip install --U pip setuptools wheel
        pip install -e ".[dev]"

Thanks!

Which version of the action are you using?

• v1
• v2
• Some other tag (such as v2.0.1 or master)

Environment

• self-hosted
• Linux
• Windows
• Mac

Python Versions
At least all versions of 3.7 and 3.8 but probably all of them