test cases:

class Box<T> {
    static <U> Box<U> make(U val) {
        interface Checker {
            void check(U val); // compile-time error
        }
        return null;
    }
}

class LocalEnum {
  static <U> U getAndSet(U u) {
    enum X {
      A;
      U u;
    }
    U old = X.A.u;
    X.A.u = u;
    return old;
  }
}

class LocalRecord {
  static <U> void test() {
    record R() {
      U get() {return null;}
    }
  }
}

reported in amber-dev by Tagir: https://mail.openjdk.java.net/pipermail/amber-dev/2020-June/006235.html