From 7f48a2a1c53ceeb5cee8fa25f1ae9f3ef1d6ac32 Mon Sep 17 00:00:00 2001
From: Erich Blume <blume.erich@gmail.com>
Date: Thu, 4 Jun 2026 12:36:12 -0700
Subject: [PATCH] infra: add cargo-fmt-check pre-push prek hook (mirror CI)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The cargo-fmt failure on this PR slipped to CI because the pre-commit
prek hooks were never installed in the working clone. The existing
cargo-fmt hook reformats in place but only when it runs. Add a
pre-push cargo-fmt-check hook (`cargo fmt --all --check`) that mirrors
CI's Dagger `check` step exactly, so an unformatted commit is blocked
locally before it can reach the runner — even if the pre-commit hook was
skipped or not installed. Filtered to .rs pushes so Rust-free pushes pay
nothing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 docs/changelog.d/prek-fmt-prepush.infra.md |  1 +
 prek.toml                                  | 16 ++++++++++++++++
 2 files changed, 17 insertions(+)
 create mode 100644 docs/changelog.d/prek-fmt-prepush.infra.md

diff --git a/docs/changelog.d/prek-fmt-prepush.infra.md b/docs/changelog.d/prek-fmt-prepush.infra.md
new file mode 100644
index 0000000..26cf000
--- /dev/null
+++ b/docs/changelog.d/prek-fmt-prepush.infra.md
@@ -0,0 +1 @@
+Added a `cargo-fmt-check` pre-push prek hook that runs `cargo fmt --all --check` (mirroring CI's Dagger `check` step) whenever a push touches a `.rs` file. The pre-commit `cargo-fmt` hook reformats in place, but only fires when installed and run; the pre-push check is a last-line guard so an unformatted commit can't reach the runner. Run `prek install --hook-type pre-push` to activate it.
diff --git a/prek.toml b/prek.toml
index 82ff957..e60082d 100644
--- a/prek.toml
+++ b/prek.toml
@@ -102,6 +102,22 @@ language = "system"
 files = '\.rs$'
 pass_filenames = false
 
+# Pre-push safety net. The pre-commit cargo-fmt hook above reformats in place,
+# but only when it is installed and actually runs — a commit made before
+# `prek install`, or via a tool that skips hooks, can still carry unformatted
+# Rust to CI (where the Dagger `check` step runs `cargo fmt --all --check` and
+# fails). This hook re-checks at push time, mirroring CI byte-for-byte, so an
+# unformatted commit is blocked locally before it can reach the runner. It runs
+# only when the push range touches a .rs file, so Rust-free pushes pay nothing.
+[[repos.hooks]]
+id = "cargo-fmt-check"
+name = "cargo-fmt-check"
+entry = "cargo fmt --all --check"
+language = "system"
+files = '\.rs$'
+pass_filenames = false
+stages = ["pre-push"]
+
 # GitHub/Forgejo Actions workflow linting
 [[repos]]
 repo = "https://github.com/rhysd/actionlint"