fix MatchedPath with Routers nested with nest_service

axum/src/extract/matched_path.rs

@@ -178,4 +178,20 @@ mod tests {
             ),
         );
     }
+
+    #[tokio::test]
+    async fn nested_opaque_routers_append_to_matched_path() {
+        let app = Router::new().nest_service(
+            "/:a",
+            Router::new().route(
+                "/:b",
+                get(|path: MatchedPath| async move { path.as_str().to_owned() }),
+            ),
+        );
+
+        let client = TestClient::new(app);
+
+        let res = client.get("/foo/bar").send().await;
+        assert_eq!(res.text().await, "/:a/:b");
+    }
 }

axum/src/routing/mod.rs

@@ -98,6 +98,7 @@ impl<B> fmt::Debug for Router<B> {
 }
 
 pub(crate) const NEST_TAIL_PARAM: &str = "__private__axum_nest_tail_param";
+const NEST_TAIL_PARAM_CAPTURE: &str = "/*__private__axum_nest_tail_param";
 
 impl<B> Router<B>
 where
@@ -416,8 +417,24 @@ where
 
         #[cfg(feature = "matched-path")]
         if let Some(matched_path) = self.node.route_id_to_path.get(&id) {
-            req.extensions_mut()
-                .insert(crate::extract::MatchedPath(Arc::clone(matched_path)));
+            use crate::extract::MatchedPath;
+
+            let matched_path = if let Some(previous) = req.extensions_mut().get::<MatchedPath>() {
+                // a previous `MatchedPath` might exist if we're inside a nested Router
+                let previous = if let Some(previous) =
+                    previous.as_str().strip_suffix(NEST_TAIL_PARAM_CAPTURE)
+                {
+                    previous
+                } else {
+                    previous.as_str()
+                };
+
+                let matched_path = format!("{}{}", previous, matched_path);
+                matched_path.into()
+            } else {
+                Arc::clone(matched_path)
+            };
+            req.extensions_mut().insert(MatchedPath(matched_path));
         } else {
             #[cfg(debug_assertions)]
             panic!("should always have a matched path for a route id");

axum/src/routing/tests/nest.rs

@@ -414,7 +414,7 @@ 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_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/");