Cannot use output from a previous step in key

[Marc Herbert]

I'm successfully fetching the digest of the latest image (before downloading the actual image) with docker manifest inspect ghcr.io/zephyrproject-rtos/ci:latest -v | jq -r '.[0].Descriptor.digest' and I'm (naively?) trying to use it in the key.

I first tried set-output as documented here: https://github.com/marketplace/actions/cache#creating-a-cache-key

      - name: get digest of latest ghcr.io/zephyrproject-rtos/ci
        id: latest-zephyr-img
        run: |
          docker manifest inspect ghcr.io/zephyrproject-rtos/ci:latest -v | jq -r '.[0].Descriptor.digest' | tee latest-img
          echo "::set-output name=date::$(cat latest-img)"

      - name: Cache Docker images
        uses: ScribeMD/docker-cache@0.2.6
        with: # can't get digest :-(
          key: zephyr-build-img-${{ steps.latest-zephyr-img.digest }}

But the value looks empty.

Then Github informed me that set-output is deprecated. So I followed the new documentation and switched to GITHUB_OUTPUT: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

      - name: get digest of latest ghcr.io/zephyrproject-rtos/ci
        id: latest-zephyr-img
        run: |
          docker manifest inspect ghcr.io/zephyrproject-rtos/ci:latest -v | jq -r '.[0].Descriptor.digest' | tee latest-img
          printf 'digest=%s\n' "$(cat latest-img)" >> "${GITHUB_OUTPUT}"

Still empty: https://github.com/thesofproject/sof/actions/runs/3851840976/jobs/6563431229
(thesofproject/sof#6918)

Is this problem specific to docker-cache?

[Kurt von Laven]

No, Actions don't have the power to control their own inputs so far as I am aware, which can be shown by attempting to use the variable from a trivial run step. My wild guess is that the colon in the value of the variable is creating issues, so maybe you need an extra set of quotes?

[Marc Herbert]

Thanks, I'll try "harder" tomorrow.

Edit: actually I won't because of #304

[Kurt von Laven]

In case this helps anyone else facing a similar issue, the problem was that steps.latest-zephyr-img.digest is not defined. You meant steps.latest-zephyr-img.outputs.digest.