From 97c8701a5a1c9e1b2439e8b7c513fd2372aa6956 Mon Sep 17 00:00:00 2001
From: jbranchaud <jbranchaud@gmail.com>
Date: Sat, 1 Feb 2025 14:10:25 -0600
Subject: [PATCH] Add Use Labels To Block PR Merge as a GitHub Actions PR

---
 README.md                                     |  3 +-
 .../use-labels-to-block-pr-merge.md           | 41 +++++++++++++++++++
 2 files changed, 43 insertions(+), 1 deletion(-)
 create mode 100644 github-actions/use-labels-to-block-pr-merge.md

diff --git a/README.md b/README.md
index 17583b0..3950d65 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1581 TILs and counting..._
+_1582 TILs and counting..._
 
 See some of the other learning resources I work on:
 - [Ruby Operator Lookup](https://www.visualmode.dev/ruby-operators)
@@ -407,6 +407,7 @@ See some of the other learning resources I work on:
 - [Disable A Workflow With The gh CLI](github-actions/disable-a-workflow-with-the-gh-cli.md)
 - [Reference An Encrypted Secret In An Action](github-actions/reference-an-encrypted-secret-in-an-action.md)
 - [Trigger A Workflow Via An API Call](github-actions/trigger-a-workflow-via-an-api-call.md)
+- [Use Labels To Block PR Merge](github-actions/use-labels-to-block-pr-merge.md)
 
 ### Go
 
diff --git a/github-actions/use-labels-to-block-pr-merge.md b/github-actions/use-labels-to-block-pr-merge.md
new file mode 100644
index 0000000..ae411b9
--- /dev/null
+++ b/github-actions/use-labels-to-block-pr-merge.md
@@ -0,0 +1,41 @@
+# 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.