codegen: auto-register HEAD guard for #[get] routes

Per RFC 7231 Section 4.3.2, a server that supports GET must also
support HEAD. The #[get] macro now implicitly registers a HEAD
guard so that HEAD requests are handled without requiring users
to write #[route("/path", method="GET", method="HEAD")].

Fixes #2702

actix-web-codegen/src/route.rs

@@ -240,6 +240,12 @@ impl Args {
 
         let is_route_macro = method.is_none();
         if let Some(method) = method {
+            // Per RFC 7231 Section 4.3.2, a server that supports GET must also
+            // support HEAD. Automatically register a HEAD guard alongside GET
+            // so that `#[get(...)]` handlers respond to HEAD requests.
+            if method == MethodType::Get {
+                methods.insert(MethodTypeExt::Standard(MethodType::Head));
+            }
             methods.insert(MethodTypeExt::Standard(method));
         }
 

actix-web-codegen/tests/routes.rs

@@ -384,3 +384,23 @@ async fn test_wrap() {
     let body = String::from_utf8(body.to_vec()).unwrap();
     assert!(body.contains("wrong number of parameters"));
 }
+
+#[get("/head-from-get")]
+async fn get_head_implicit() -> impl Responder {
+    HttpResponse::Ok().body("hello")
+}
+
+#[actix_web::test]
+async fn test_get_implies_head() {
+    let srv = actix_test::start(|| App::new().service(get_head_implicit));
+
+    // GET should work as usual
+    let request = srv.request(http::Method::GET, srv.url("/head-from-get"));
+    let response = request.send().await.unwrap();
+    assert_eq!(response.status(), StatusCode::OK);
+
+    // HEAD should also work on a #[get] endpoint per RFC 7231
+    let request = srv.request(http::Method::HEAD, srv.url("/head-from-get"));
+    let response = request.send().await.unwrap();
+    assert_eq!(response.status(), StatusCode::OK);
+}