delete_branch_cache.yml

# yamllint disable rule:line-length
# yaml-language-server: $schema=https://json.schemastore.org/github-workflow.json
---
# Taken from https://github.com/actions/cache/blob/main/tips-and-workarounds.md#force-deletion-of-caches-overriding-default-cache-eviction-policy
name: cleanup caches by a branch
on:  # yamllint disable-line rule:truthy
  pull_request:
    types:
      - closed
  workflow_dispatch:

jobs:
  cleanup:
    runs-on: ubuntu-latest
    steps:
      - name: Cleanup
        run: |
          gh extension install actions/gh-actions-cache

          set -x
          REPO=${{ github.repository }}
          # The github.ref should be refs/pull/XXX/merge, but for some reason, it was set to 'main' in an actual run. Debugging this would be a ginormous pain, since it can apparently only be properly done on an actual merge/close (when I tried testing it locally with a close, it *did* work!), and so we'll just set this manually and ignore it for now. Accidentally deleting the caches on main is unacceptable.
          # BRANCH=${{ github.ref }}
          BRANCH=${PR_TARGET_NAME}

          echo "Fetching list of cache key"
          cacheKeysForPR=$(gh actions-cache list -R $REPO -B $BRANCH | cut -f 1 )

          ## Setting this to not fail the workflow while deleting cache keys.
          set +e
          echo "Deleting caches..."
          for cacheKey in $cacheKeysForPR
          do
              gh actions-cache delete $cacheKey -R $REPO -B $BRANCH --confirm
          done
          echo "Done"
        env:
          # Note that this can only run on branches from the repo; otherwise, we don't have write permissions so we can't delete the caches
          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
          PR_TARGET_NAME: ${{ format('refs/pull/{0}/merge', github.event.number) }}