Access GitHub Actions Artifacts across runs

GitHub actions allows you to store artifacts to retrieve later. One confusing aspect is that it’s only really designed to work inside the same workflow run.

Let’s say when submitting a pull request, you wanted to compare test coverage between that PR and main. You could do (shortened for readability):

jobs:
  test-pr:
    steps:
    - uses: actions/checkout@v5
    # setup etc
    - name: Test
      run: pnpm test --coverage
    - name: Store coverage
      uses: actions/upload-artifact@v6
      with:
        name: coverage-pr
        path: coverage/
  test-main:
    steps:
    - uses: actions/checkout@v5
      with:
        ref: main
    # setup etc
    - name: Test
      run: pnpm test --coverage
    - name: Store coverage
      uses: actions/upload-artifact@v6
      with:
        name: coverage-main
        path: coverage/
  compare-coverage:
    needs: [test-pr, test-main]
    steps:
    - uses: actions/download-artifact@v7
      with:
        name: coverage-pr
        path: ./coverage-pr
    - uses: actions/download-artifact@v7
      with:
        name: coverage-main
        path: ./coverage-main
    - name: Report coverage
      # Coverage action goes here

The “main” problem may stand out to you.

Pun intended! We are running the tests twice for each PR workflow run: once against main and once against our PR. This is both wasteful and slow. As only the branch is changing, we should only need to re-run tests against the branch.

Most repositories I work on run tests against main on merge, requiring the tests pass before deployment. In this scenario we know we’ve run the tests before, and it shouldn’t need to be repeated. We can store the coverage when the tests are run on main, and then retrieve them in PRs.

Unfortunately GitHub Actions doesn’t make supporting this easy. As each artifact is bound to a run id, you’ll need to know that first.

We’re going to use the Github CLI for this, because you get it for free when running scripts under GitHub Actions:

gh api \
  repos/$ORG/$REPO/actions/workflows/$ACTION_FILENAME>/runs \
  -q "first(.workflow_runs[] | select( \
        .head_branch == \"main\" and \
        .status == \"completed\" and \
        .conclusion == \"success\")).id"

In Github, $ORG\$REPO will be ${{ github.repository }}. $ACTION_FILENAME is the literal file name on disk inside your /actions/workflows/ directory of your repo: eg cicd.yaml.

Once you have run id you can request your artifact with that run id (again, shortened for readability):

jobs:
  test-pr:
    steps:
    - uses: actions/checkout@v5
    # setup etc
    - name: Test
      run: pnpm test --coverage
    - name: Store coverage
      uses: actions/upload-artifact@v6
      with:
        name: coverage-pr
        path: coverage/
  compare-coverage:
    needs: [test-pr, test-main]
    steps:
    - name: Get last main run id
      id: main_run_id
      run: |
        RUN_ID=$(gh api \
		  repos/${{ githuv.repository }}$/actions/workflows/cicd.yaml/runs \
          -q "first(.workflow_runs[] | select( \
            .head_branch == \"main\" and \
            .status == \"completed\" and \
            .conclusion == \"success\"
          )).id"
        )
        
        echo "run_uid=$RUN_id" >> $GITHUB_OUTPUT
    - uses: actions/download-artifact@v7
      with:
        name: coverage-pr
        path: ./coverage-pr
    - uses: actions/download-artifact@v7
      with:
        name: coverage-main
        # New bit! We are presuming that this has been generated in cicd.yaml
        run-id: ${{ steps.main_run_id.outputs.run_id }} 
        path: ./coverage-main
    - name: Report coverage
      # Coverage action goes here