Add regression test

Author: ahejlsberg

tests/cases/conformance/types/conditional/conditionalTypes1.ts

@@ -341,3 +341,15 @@ declare interface ExtractFooBar<FB extends FooBar> { }
 type Extracted<Struct> = {
     [K in keyof Struct]: Struct[K] extends FooBar ? ExtractFooBar<Struct[K]> : Struct[K];
 }
+
+// Repro from #22985
+
+type RecursivePartial<T> = {
+  [P in keyof T]?: T[P] extends Array<any> ? {[index: number]: RecursivePartial<T[P][0]>} :
+    T[P] extends object ? RecursivePartial<T[P]> : T[P];
+};
+
+declare function assign<T>(o: T, a: RecursivePartial<T>): void;
+
+var a = {o: 1, b: 2, c: [{a: 1, c: '213'}]}
+assign(a, {o: 2, c: {0: {a: 2, c: '213123'}}})