checker/tests/nullness/java-unsound/Figure7.java

// Unsound only in Java 8, Java 9+ already gives an error
// @skip-test no need to test for the javac error.

public class Figure7<T, U> {
  class Constrain<B extends U> {}

  final Constrain<? super T> constrain;
  final U u;

  Figure7(T t) {
    u = coerce(t);
    constrain = getConstrain();
  }

  <B extends U> U upcast(Constrain<B> constrain, B b) {
    return b;
  }

  U coerce(T t) {
    // :: error: method upcast in class Figure7<T,U> cannot be applied to given types;
    return upcast(constrain, t);
  }

  Constrain<? super T> getConstrain() {
    return constrain;
  }

  public static void main(String[] args) {
    String zero = new Figure7<Integer, String>(0).u;
  }
}