Add regression test

Author: ahejlsberg

tests/cases/conformance/types/keyof/keyofAndIndexedAccess.ts

@@ -505,3 +505,15 @@ function updateIds2<T extends { [x: string]: string }, K extends keyof T>(
 // Repro from #13514
 
 declare function head<T extends Array<any>>(list: T): T[0];
+
+// Repro from #13604
+
+class A<T> {
+	props: T & { foo: string };
+}
+
+class B extends A<{ x: number}> {
+	f(p: this["props"]) {
+		p.x;
+	}
+}