The following program does not compile:

```
abstract sealed class J<T1, T2> permits X.S, A {}

final class A extends J<Integer, String> {}

public class X<T> {

    final class S<U> extends J<T, U> {}

    int testExhaustive(J<Integer, String> ji) {
        return switch (ji) {
            case A a -> 42;
            case X<Integer>.S<String> e -> 4200;
        };
    }
    public static void main(String[] args) {
        X<Integer>.S<String> xs = null;
        System.out.println(new X<Integer>().testExhaustive(new X<Integer>().new S<String>()));
    }
}
```

See:
https://mail.openjdk.org/pipermail/compiler-dev/2024-November/028464.html