Cache-Hit output is null

[MarcoJanecki]

Hey guys! :)

We are currently trying to implement caching for Docker layers using the v4 Action.

We encountered the problem, that the outputs are always empty (i.e. outputs.cache-hit == null). We already investigated into almost every edge case and became stuck.

If I interpret the documentation correctly, such a missing output should never occur (should always be either true or false?)

Those are the respective steps from our Github Workflow:

- name: Docker layers caching
        id: cache-docker
        uses: actions/cache@v4
        continue-on-error: true
        with:
          fail-on-cache-miss: true
          path: /tmp/docker-cache
          key: ${{ runner.os }}-docker-${{ hashFiles('docker/docker-compose.yaml') }}

      - name: Check cache hit
        run: |
           echo "Cache hit: ${{ toJson(steps.cache-docker.outputs.cache-hit) }}"
           echo "Output hit: ${{ toJson(steps.cache-docker.outputs) }}"
           echo "Output hit: ${{ toJson(steps.cache-docker.outcome) }}"
           echo "Cache hit is true: ${{ steps.cache-docker.outputs.cache-hit == 'true'}}"
           echo "Cache hit is false: ${{ steps.cache-docker.outputs.cache-hit == 'false'}}"

Output step "Docker layers caching":

Run actions/cache@v4
  with:
    fail-on-cache-miss: true
    path: /tmp/docker-cache
    key: Linux-docker-768b87720c2e53c457935d1efe1ba2781796490829eaecdc0667cbfa08bcd50e
    enableCrossOsArchive: false
    lookup-only: false
    save-always: false
  env:
    pythonLocation: /opt/hostedtoolcache/Python/3.11.9/x64
    PKG_CONFIG_PATH: /opt/hostedtoolcache/Python/3.11.9/x64/lib/pkgconfig
    Python_ROOT_DIR: /opt/hostedtoolcache/Python/3.11.9/x64
    Python2_ROOT_DIR: /opt/hostedtoolcache/Python/3.11.9/x64
    Python3_ROOT_DIR: /opt/hostedtoolcache/Python/3.11.9/x64
    LD_LIBRARY_PATH: /opt/hostedtoolcache/Python/3.11.9/x64/lib
Error: Failed to restore cache entry. Exiting as fail-on-cache-miss is set. Input key: Linux-docker-768b87720c2e53c457935d1efe1ba2781796490829eaecdc0667cbfa08bcd50e

Output step "Check cache hit":

Run echo "Cache hit: null"
Cache hit: null
Output hit: {}
Output hit: failure
Cache hit is true: false
Cache hit is false: false

Are we essentially doing something wrong?

Any help is appreciated! Thanks in advance! :)

[joshmgross]

This should be fixed by #1404, which will be released in the next version update.

[joshmgross]

This will be included in 4.1.0 - https://github.com/actions/cache/pull/1464

[joshmgross]

https://github.com/actions/cache/releases/tag/v4.1.0