Add Use Labels To Block PR Merge as a GitHub Actions PR

github-actions/use-labels-to-block-pr-merge.md

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+# Use Labels To Block PR Merge
+
+Let's say our GitHub project has custom tags for both `no merge` and `wip`
+(_work in progress_). Whenever either of those labels has been applied to a PR,
+we want there to be a failed check so as to block the merge. This is useful to
+ensure automated tools (as well as someone not looking closely enough) don't
+merge a PR that isn't _ready to go_.
+
+This can be achieved with a basic GitHub Actions workflow that requires no
+3rd-party actions. We can add the following as
+`.github/workflows/block-labeled-prs.yml` in our project.
+
+```yaml
+name: Block Labeled PR Merges
+
+on:
+  pull_request:
+    types: [labeled, unlabeled, opened, edited, synchronize]
+
+jobs:
+  prevent-merge:
+    if: ${{ contains(github.event.*.labels.*.name, 'no merge') || contains(github.event.*.labels.*.name, 'wip') }}
+    name: Prevent Merging
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check for label
+        run: |
+          echo "Pull request label prevents merging."
+          echo "Labels: ${{ join(github.event.*.labels.*.name, ', ') }}"
+          echo "Remove the blocking label(s) to skip this check."
+          exit 1
+```
+
+This workflow is run when a pull request is opened, when it is edited or
+synchronized, and when a label change is made. The job `prevent-merge` sees if
+any of the label names match `no merge` or `wip`. If so, we echo out some
+details in the ubuntu container and then `exit 1` to fail the check.
+
+Shoutout to [Jesse Squire's
+implementation](https://www.jessesquires.com/blog/2021/08/24/useful-label-based-github-actions-workflows/#updated-21-march-2022)
+which I've heavily borrowed from here.