fix(node): keep fastify routerPath for backwards compatibility

Author: Zen-cronic

packages/node/src/integrations/tracing/fastify.ts

@@ -30,6 +30,8 @@ interface FastifyRequestRouteInfo {
     url?: string;
     method?: string;
   };
+  // will deprecate in Fastify 5
+  routerPath?: string;
 }
 
 const INTEGRATION_NAME = 'Fastify';
@@ -78,7 +80,8 @@ export function setupFastifyErrorHandler(fastify: Fastify): void {
 
         // Taken from Otel Fastify instrumentation:
         // https://github.com/open-telemetry/opentelemetry-js-contrib/blob/main/plugins/node/opentelemetry-instrumentation-fastify/src/instrumentation.ts#L94-L96
-        const routeName = reqWithRouteInfo.routeOptions?.url;
+        const routeName = reqWithRouteInfo.routeOptions ? reqWithRouteInfo.routeOptions.url : reqWithRouteInfo.routerPath;
+
         const method = reqWithRouteInfo.routeOptions?.method || 'GET';
 
         getIsolationScope().setTransactionName(`${method} ${routeName}`);