recurse whole object (#5118)

* failing test

* simple yet breaking oversight

* add changeset

.changeset/nine-rats-bake.md

@@ -0,0 +1,5 @@
+---
+"@sveltejs/kit": patch
+---
+
+fix `BodyValidator` handling for nested object literals

packages/kit/test/typings/endpoint.test.ts

@@ -104,6 +104,23 @@ export const nested_interfaces: RequestHandler<Record<string, string>, ParentWra
 	};
 };
 
+interface NestedLiteral {
+	date: {
+		published: string;
+		updated?: string;
+		time: {
+			hour: number;
+			min: number;
+			sec?: number;
+		};
+	};
+}
+export const nested_literal: RequestHandler<Record<string, string>, NestedLiteral> = () => {
+	return {
+		body: {} as NestedLiteral
+	};
+};
+
 // --- invalid cases ---
 
 // @ts-expect-error - bigint cannot be converted to JSON string

packages/kit/types/private.d.ts

@@ -27,8 +27,8 @@ export interface AdapterEntry {
 }
 
 export type BodyValidator<T> = {
-	[P in keyof T]: T[P] extends { [k: string]: infer V }
-		? BodyValidator<V> // recurse when T[P] is an object
+	[P in keyof T]: T[P] extends { [k: string]: unknown }
+		? BodyValidator<T[P]> // recurse when T[P] is an object
 		: T[P] extends BigInt | Function | Symbol
 		? never
 		: T[P];