Fix axum path nesting (#1231)

Fix axum path nesting in `OpenApiRouter` to allow empty paths and
correctly template the path for `OpenApiRouter` from colons.

Relates to #1199

utoipa-axum/CHANGELOG.md

@@ -4,6 +4,7 @@
 
 ### Fixed
 
+* Fix axum path nesting (https://github.com/juhaku/utoipa/pull/1231)
 * Fix diverging axum route and openapi spec (https://github.com/juhaku/utoipa/pull/1199)
 
 ## 0.1.2 - Oct 29 2024

utoipa-axum/src/router.rs

@@ -322,23 +322,23 @@ where
     pub fn nest(self, path: &str, router: OpenApiRouter<S>) -> Self {
         // from axum::routing::path_router::path_for_nested_route
         // method is private, so we need to replicate it here
-        fn path_for_nested_route<'a>(prefix: &'a str, path: &'a str) -> String {
+        fn path_for_nested_route(prefix: &str, path: &str) -> String {
+            let path = if path.is_empty() { "/" } else { path };
             debug_assert!(prefix.starts_with('/'));
-            debug_assert!(path.starts_with('/'));
 
             if prefix.ends_with('/') {
-                format!("{prefix}{}", path.trim_start_matches('/')).into()
+                format!("{prefix}{}", path.trim_start_matches('/'))
             } else if path == "/" {
                 prefix.into()
             } else {
-                format!("{prefix}{path}").into()
+                format!("{prefix}{path}")
             }
         }
 
         let api = self.1.nest_with_path_composer(
-            path_for_nested_route(path, "/"),
+            path_for_nested_route(&path_template(path), "/"),
             router.1,
-            |a: &str, b: &str| path_for_nested_route(a, b),
+            path_for_nested_route,
         );
         let router = self.0.nest(&colonized_params(path), router.0);