From 92f6b68390120cdf973f11d98bc64ff45f2ca644 Mon Sep 17 00:00:00 2001
From: Jonas Platte <jplatte+git@posteo.de>
Date: Thu, 25 Aug 2022 15:42:17 +0200
Subject: [PATCH] Panic when attempting to add a route_layer to an empty router
 (#1327)

---
 axum/CHANGELOG.md                  |  8 +++++++-
 axum/src/routing/method_routing.rs | 16 ++++++++++++++++
 axum/src/routing/mod.rs            |  8 ++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/axum/CHANGELOG.md b/axum/CHANGELOG.md
index cace7db3..705b26ce 100644
--- a/axum/CHANGELOG.md
+++ b/axum/CHANGELOG.md
@@ -7,7 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
-- None
+## Routing
+
+- **breaking:** Adding a `.route_layer` onto a `Router` or `MethodRouter`
+  without any routes will now result in a panic. Previously, this just did
+  nothing. [#1327]
+
+[#1327]: https://github.com/tokio-rs/axum/pull/1327
 
 # 0.6.0-rc.1 (23. August, 2022)
 
diff --git a/axum/src/routing/method_routing.rs b/axum/src/routing/method_routing.rs
index e28a9e93..c3a69106 100644
--- a/axum/src/routing/method_routing.rs
+++ b/axum/src/routing/method_routing.rs
@@ -852,6 +852,7 @@ where
     }
 
     #[doc = include_str!("../docs/method_routing/route_layer.md")]
+    #[track_caller]
     pub fn route_layer<L>(mut self, layer: L) -> MethodRouter<S, B, E>
     where
         L: Layer<Route<B, E>>,
@@ -859,6 +860,21 @@ where
         <L::Service as Service<Request<B>>>::Response: IntoResponse + 'static,
         <L::Service as Service<Request<B>>>::Future: Send + 'static,
     {
+        if self.get.is_none()
+            && self.head.is_none()
+            && self.delete.is_none()
+            && self.options.is_none()
+            && self.patch.is_none()
+            && self.post.is_none()
+            && self.put.is_none()
+            && self.trace.is_none()
+        {
+            panic!(
+                "Adding a route_layer before any routes is a no-op. \
+                 Add the routes you want the layer to apply to first."
+            );
+        }
+
         let layer_fn = |svc| {
             let svc = layer.layer(svc);
             let svc = MapResponseLayer::new(IntoResponse::into_response).layer(svc);
diff --git a/axum/src/routing/mod.rs b/axum/src/routing/mod.rs
index 8bcbbe22..3f75a968 100644
--- a/axum/src/routing/mod.rs
+++ b/axum/src/routing/mod.rs
@@ -352,6 +352,7 @@ where
     }
 
     #[doc = include_str!("../docs/routing/route_layer.md")]
+    #[track_caller]
     pub fn route_layer<L>(self, layer: L) -> Self
     where
         L: Layer<Route<B>>,
@@ -360,6 +361,13 @@ where
         <L::Service as Service<Request<B>>>::Error: Into<Infallible> + 'static,
         <L::Service as Service<Request<B>>>::Future: Send + 'static,
     {
+        if self.routes.is_empty() {
+            panic!(
+                "Adding a route_layer before any routes is a no-op. \
+                 Add the routes you want the layer to apply to first."
+            );
+        }
+
         let layer = ServiceBuilder::new()
             .map_err(Into::into)
             .layer(MapResponseLayer::new(IntoResponse::into_response))