Panic when attempting to add a route_layer to an empty router (#1327)

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)
 

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);

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))