#[must_use] all the things! (#1809)

axum/CHANGELOG.md

@@ -7,12 +7,13 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
+- **fixed:** Add `#[must_use]` attributes to types that do nothing unless used ([#1809])
 - **fixed:** Add `#[must_use]` to `WebSocketUpgrade::on_upgrade` ([#1801])
 - **fixed:** Fix routing issues when loading a `Router` via a dynamic library ([#1806])
 
-[#1806]: https://github.com/tokio-rs/axum/pull/1806
-
 [#1801]: https://github.com/tokio-rs/axum/pull/1801
+[#1806]: https://github.com/tokio-rs/axum/pull/1806
+[#1809]: https://github.com/tokio-rs/axum/pull/1809
 
 # 0.6.9 (24. February, 2023)
 

axum/src/body/stream_body.rs

@@ -52,6 +52,7 @@ pin_project! {
     /// ```
     ///
     /// [`Stream`]: futures_util::stream::Stream
+    #[must_use]
     pub struct StreamBody<S> {
         #[pin]
         stream: SyncWrapper<S>,

axum/src/extension.rs

@@ -70,6 +70,7 @@ use tower_service::Service;
 /// struct Foo(&'static str);
 /// ```
 #[derive(Debug, Clone, Copy, Default)]
+#[must_use]
 pub struct Extension<T>(pub T);
 
 #[async_trait]

axum/src/form.rs

@@ -61,6 +61,7 @@ use std::ops::Deref;
 /// [`Multipart`]: crate::extract::Multipart
 #[cfg_attr(docsrs, doc(cfg(feature = "form")))]
 #[derive(Debug, Clone, Copy, Default)]
+#[must_use]
 pub struct Form<T>(pub T);
 
 #[async_trait]

axum/src/json.rs

@@ -97,6 +97,7 @@ use std::ops::{Deref, DerefMut};
 /// ```
 #[derive(Debug, Clone, Copy, Default)]
 #[cfg_attr(docsrs, doc(cfg(feature = "json")))]
+#[must_use]
 pub struct Json<T>(pub T);
 
 #[async_trait]

axum/src/middleware/from_extractor.rs

@@ -110,6 +110,7 @@ pub fn from_extractor_with_state<E, S>(state: S) -> FromExtractorLayer<E, S> {
 /// See [`from_extractor`] for more details.
 ///
 /// [`Layer`]: tower::Layer
+#[must_use]
 pub struct FromExtractorLayer<E, S> {
     state: S,
     _marker: PhantomData<fn() -> E>,

axum/src/middleware/from_fn.rs

@@ -161,6 +161,7 @@ pub fn from_fn_with_state<F, S, T>(state: S, f: F) -> FromFnLayer<F, S, T> {
 /// [`tower::Layer`] is used to apply middleware to [`Router`](crate::Router)'s.
 ///
 /// Created with [`from_fn`]. See that function for more details.
+#[must_use]
 pub struct FromFnLayer<F, S, T> {
     f: F,
     state: S,

axum/src/middleware/map_request.rs

@@ -165,6 +165,7 @@ pub fn map_request_with_state<F, S, T>(state: S, f: F) -> MapRequestLayer<F, S,
 /// A [`tower::Layer`] from an async function that transforms a request.
 ///
 /// Created with [`map_request`]. See that function for more details.
+#[must_use]
 pub struct MapRequestLayer<F, S, T> {
     f: F,
     state: S,

axum/src/middleware/map_response.rs

@@ -149,6 +149,7 @@ pub fn map_response_with_state<F, S, T>(state: S, f: F) -> MapResponseLayer<F, S
 /// A [`tower::Layer`] from an async function that transforms a response.
 ///
 /// Created with [`map_response`]. See that function for more details.
+#[must_use]
 pub struct MapResponseLayer<F, S, T> {
     f: F,
     state: S,

axum/src/response/mod.rs

@@ -39,6 +39,7 @@ pub use sse::Sse;
 ///
 /// Will automatically get `Content-Type: text/html`.
 #[derive(Clone, Copy, Debug)]
+#[must_use]
 pub struct Html<T>(pub T);
 
 impl<T> IntoResponse for Html<T>
@@ -98,7 +99,7 @@ mod tests {
             }
         }
 
-        Router::<(), Body>::new()
+        _ = Router::<(), Body>::new()
             .route("/", get(impl_trait_ok))
             .route("/", get(impl_trait_err))
             .route("/", get(impl_trait_both))
@@ -208,7 +209,7 @@ mod tests {
             )
         }
 
-        Router::<(), Body>::new()
+        _ = Router::<(), Body>::new()
             .route("/", get(status))
             .route("/", get(status_headermap))
             .route("/", get(status_header_array))

axum/src/response/sse.rs

@@ -53,6 +53,7 @@ use tokio::time::Sleep;
 
 /// An SSE response
 #[derive(Clone)]
+#[must_use]
 pub struct Sse<S> {
     stream: S,
     keep_alive: Option<KeepAlive>,
@@ -163,6 +164,7 @@ where
 
 /// Server-sent event
 #[derive(Debug, Default, Clone)]
+#[must_use]
 pub struct Event {
     buffer: BytesMut,
     flags: EventFlags,
@@ -383,6 +385,7 @@ bitflags::bitflags! {
 /// Configure the interval between keep-alive messages, the content
 /// of each message, and the associated stream.
 #[derive(Debug, Clone)]
+#[must_use]
 pub struct KeepAlive {
     event: Bytes,
     max_interval: Duration,

axum/src/routing/method_routing.rs

@@ -513,6 +513,7 @@ where
 ///     S: Service<Request<Body>>,
 /// {}
 /// ```
+#[must_use]
 pub struct MethodRouter<S = (), B = Body, E = Infallible> {
     get: MethodEndpoint<S, B, E>,
     head: MethodEndpoint<S, B, E>,

axum/src/routing/mod.rs

@@ -48,6 +48,7 @@ pub use self::method_routing::{
 pub(crate) struct RouteId(u32);
 
 /// The router type for composing handlers and services.
+#[must_use]
 pub struct Router<S = (), B = Body> {
     routes: HashMap<RouteId, Endpoint<S, B>>,
     node: Arc<Node>,

axum/src/routing/tests/mod.rs

@@ -522,7 +522,7 @@ fn routes_with_overlapping_method_routes() {
 fn merging_with_overlapping_method_routes() {
     async fn handler() {}
     let app: Router = Router::new().route("/foo/bar", get(handler));
-    app.clone().merge(app);
+    _ = app.clone().merge(app);
 }
 
 #[crate::test]

axum/src/routing/tests/nest.rs

@@ -257,7 +257,7 @@ async fn multiple_top_level_nests() {
 #[crate::test]
 #[should_panic(expected = "Invalid route: nested routes cannot contain wildcards (*)")]
 async fn nest_cannot_contain_wildcards() {
-    Router::<(), Body>::new().nest("/one/*rest", Router::new());
+    _ = Router::<(), Body>::new().nest("/one/*rest", Router::new());
 }
 
 #[crate::test]

axum/src/typed_header.rs

@@ -50,6 +50,7 @@ use std::{convert::Infallible, ops::Deref};
 /// ```
 #[cfg(feature = "headers")]
 #[derive(Debug, Clone, Copy)]
+#[must_use]
 pub struct TypedHeader<T>(pub T);
 
 #[async_trait]