do_not_merge.yml

name: Do Not Merge

on:
  pull_request:
    types: [synchronize, opened, reopened, labeled, unlabeled]

jobs:
  do-not-merge:
    name: Blocked by label
    runs-on: ubuntu-latest
    steps:
      - name: Fail if 'status:do-not-merge' label is present
        id: check-label
        env:
          LABELS_JSON: ${{ toJson(github.event.pull_request.labels) }}
        run: |
          set -x

          # The multiline string needs to be reformed into 'real' JSON again
          MATCH=$(jq -Rs 'fromjson | map(select(.name == "status:do-not-merge")) | length' <<<"$LABELS_JSON")

          if [ "$MATCH" -gt 0 ]; then
            echo "Label 'status:do-not-merge' is present. Failing the job."
            echo "found=true" >> "$GITHUB_OUTPUT"
          else
            echo "Label 'status:do-not-merge' is NOT present. Passing."
            echo "found=false" >> "$GITHUB_OUTPUT"
          fi

      - name: Fail if label is present
        if: steps.check-label.outputs.found == 'true'
        run: |
          echo "❌ Label 'status:do-not-merge' is present. Failing the job."
          exit 1