From 413bdb7b38e578d882a72fb8e00819c0ee1b7370 Mon Sep 17 00:00:00 2001
From: jeffrey-signal <jeffrey@signal.org>
Date: Tue, 9 Dec 2025 12:14:35 -0500
Subject: [PATCH] Add optional git hook to run formatter pre-push.

---
 .gitignore      |  1 +
 CONTRIBUTING.md |  2 +-
 lefthook.yml    | 15 +++++++++++++++
 3 files changed, 17 insertions(+), 1 deletion(-)
 create mode 100644 lefthook.yml

diff --git a/.gitignore b/.gitignore
index 108cb8f44c..c397d8b78f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -32,3 +32,4 @@ maps.key
 /local/
 kls_database.db
 .kotlin
+lefthook-local.yml
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 85a72a099e..14c045a7a0 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -62,7 +62,7 @@ You will need to [sign our CLA](https://signal.org/cla/) before your pull reques
 ### Follow the Code Style Guidelines
 Ensure that your code adheres to the [Code Style Guidelines](https://github.com/signalapp/Signal-Android/wiki/Code-Style-Guidelines) before submitting a pull request.
 
-You can run `./gradlew format` to automatically check conformance with some of these guidelines.
+You can run `./gradlew format` to automatically format your code. See `lefthook.yml` for instructions on how to run this as a git hook.
 
 ### Submit finished and well-tested pull requests
 Please do not submit pull requests that are still a work in progress. Pull requests should be thoroughly tested and ready to merge before they are submitted.
diff --git a/lefthook.yml b/lefthook.yml
new file mode 100644
index 0000000000..86930d34b9
--- /dev/null
+++ b/lefthook.yml
@@ -0,0 +1,15 @@
+# Lefthook git hooks configuration
+#
+# ========== SETUP ==========
+# 1. Install lefthook: https://lefthook.dev/installation/
+# 2. Enable hooks: lefthook install
+#
+# ========== CUSTOMIZATION ==========
+# Create lefthook-local.yml (gitignored) to override settings locally.
+# https://lefthook.dev/examples/lefthook-local.html
+
+pre-push:
+  commands:
+    format:
+      run: ./gradlew format --quiet && test -z "$(git status --porcelain)"
+      fail_text: "Formatting changes detected. Please commit them and push again."