404 when including github.ref in key

With config like this:

    - name: Ubuntu cache
      uses: actions/cache@preview
      if: startsWith(matrix.os, 'ubuntu')
      with:
        path: ~/.cache/pip
        key: ${{ github.workflow }}-${{ github.ref }}-${{ matrix.os }}-${{ matrix.python-version }}

    - name: macOS cache
      uses: actions/cache@preview
      if: startsWith(matrix.os, 'macOS')
      with:
        path: ~/Library/Caches/pip
        key: ${{ github.workflow }}-${{ github.ref }}-${{ matrix.os }}-${{ matrix.python-version }}

It creates a key like "Test-refs/heads/gha-cache-ubuntu-18.04-3.5".

The upload step fails with a 404:

Post Ubuntu cache1s
##[warning]Cache service responded with 404
Post job cleanup.
/bin/tar -cz -f /home/runner/work/_temp/802beeb6-cc68-45cb-a68d-488cc4008df5/cache.tgz -C /home/runner/.cache/pip .
##[warning]Cache service responded with 404

eg. https://github.com/hugovk/Pillow/runs/286812478#step:22:1

That’s because github.ref includes slashes (eg. refs/heads/gha-cache):

The branch or tag ref that triggered the workflow. For example, refs/heads/feature-branch-1. If neither a branch or tag is available for the event type, the variable will not exist.

https://help.github.com/en/github/automating-your-workflow-with-github-actions/virtual-environments-for-github-actions#environment-variables

Should I escape or replace illegal characters (and how?) or should the Action take care of them?

Or is there another way to include the branch name in the key?

[joshmgross]

Does that include “inheriting” the caches from the base branch of a pull request? ie when building a pull request targeting master the first time, will that pick up the cache from master?

Yep, PRs are able to read from the cache of master (or default branch) but will write to the cache of the PR branch. We’re working on more comprehensive documentation.

[joshmgross]

@chancancode check out: https://help.github.com/en/github/automating-your-workflow-with-github-actions/caching-dependencies-to-speed-up-workflows#cache-scope