Add this positive test to test/tools/javac:

public class X<T extends Runnable> implements Runnable {

      void foo0(X<X<?>> lhs, X<X<? extends Runnable>> rhs) {
            lhs = rhs; // 0
      }
      void foo1(X<X<?>> lhs, X<X<? extends Object>> rhs) {
            lhs = rhs; // 1
      }
      public void run() {
      }
}