Fix inconsistent double slash when nesting routes (#824)

axum/CHANGELOG.md

@@ -60,6 +60,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - **breaking:** `AddExtensionLayer` has been removed. Use `Extension` instead. It now implements
   `tower::Layer` ([#807])
 - **breaking:** `AddExtension` has been moved from the root module to `middleware`
+- **breaking:** `.nest("/foo/", Router::new().route("/bar", _))` now does the right thing and
+  results in a route at `/foo/bar` instead of `/foo//bar` ([#824])
 - **breaking:** Routes are now required to start with `/`. Previously routes such as `:foo` would
   be accepted but most likely result in bugs ([#823])
 - **fixed:** Set `Allow` header when responding with `405 Method Not Allowed` ([#733])
@@ -85,6 +87,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 [#807]: https://github.com/tokio-rs/axum/pull/807
 [#819]: https://github.com/tokio-rs/axum/pull/819
 [#823]: https://github.com/tokio-rs/axum/pull/823
+[#824]: https://github.com/tokio-rs/axum/pull/824
 
 # 0.4.4 (13. January, 2022)
 

axum/src/routing/mod.rs

@@ -215,6 +215,8 @@ where
                         path.into()
                     } else if path == "/" {
                         (&*nested_path).into()
+                    } else if let Some(path) = path.strip_suffix('/') {
+                        format!("{}{}", path, nested_path).into()
                     } else {
                         format!("{}{}", path, nested_path).into()
                     };

axum/src/routing/tests/nest.rs

@@ -345,3 +345,37 @@ async fn outer_middleware_still_see_whole_url() {
     );
     assert_eq!(client.get("/one/two").send().await.text().await, "/one/two");
 }
+
+macro_rules! nested_route_test {
+    (
+        $name:ident,
+        nest = $nested_path:literal,
+        route = $route_path:literal,
+        expected = $expected_path:literal $(,)?
+    ) => {
+        #[tokio::test]
+        async fn $name() {
+            let inner = Router::new().route($route_path, get(|| async {}));
+            let app = Router::new().nest($nested_path, inner);
+            let client = TestClient::new(app);
+            assert_eq!(
+                client.get($expected_path).send().await.status(),
+                StatusCode::OK
+            );
+        }
+    };
+}
+
+// test cases taken from https://github.com/tokio-rs/axum/issues/714#issuecomment-1058144460
+nested_route_test!(nest_1, nest = "", route = "/", expected = "/");
+nested_route_test!(nest_2, nest = "", route = "/a", expected = "/a");
+nested_route_test!(nest_3, nest = "", route = "/a/", expected = "/a/");
+nested_route_test!(nest_4, nest = "/", route = "/", expected = "/");
+nested_route_test!(nest_5, nest = "/", route = "/a", expected = "/a");
+nested_route_test!(nest_6, nest = "/", route = "/a/", expected = "/a/");
+nested_route_test!(nest_7, nest = "/a", route = "/", expected = "/a");
+nested_route_test!(nest_8, nest = "/a", route = "/a", expected = "/a/a");
+nested_route_test!(nest_9, nest = "/a", route = "/a/", expected = "/a/a/");
+nested_route_test!(nest_11, nest = "/a/", route = "/", expected = "/a/");
+nested_route_test!(nest_12, nest = "/a/", route = "/a", expected = "/a/a");
+nested_route_test!(nest_13, nest = "/a/", route = "/a/", expected = "/a/a/");