checker/tests/nullness/generics/WildcardSuper.java

import org.checkerframework.checker.nullness.qual.*;
import org.checkerframework.framework.qual.DefaultQualifier;

public class WildcardSuper {

  void testWithSuper(Cell<? super @NonNull String> cell) {
    // TODO: Address comments.  Since ? is explicitly lower bounded, I have made a judgment that
    // it should be implicitly upper bounded.
    // This is valid because the default upper bound is NonNull
    // :: error: (dereference.of.nullable)
    cell.get().toString();
  }

  // TODO: THIS SHOULD JUST ISSUE A WARNING, WHY WOULD PEOPLE WANT TO WRITE CONTRADICTING BOUNDS?
  void testWithContradiction(Cell<? super @Nullable String> cell) {
    // This is actually valid, because it's a contradiction, because
    // the implicit upper bound is NonNull.
    // We are free to do anything, as the method is not callable.
    // TODO: test whether all calls of method fail.
    // :: error: (dereference.of.nullable)
    cell.get().toString();
  }

  @DefaultQualifier(Nullable.class)
  void testWithImplicitNullable(@NonNull Cell<? super @NonNull String> cell) {
    // :: error: (dereference.of.nullable)
    cell.get().toString();
  }

  void testWithExplicitNullable(Cell<@Nullable ? extends @Nullable String> cell) {
    // :: error: (dereference.of.nullable)
    cell.get().toString();
  }

  void testWithDoubleNullable(Cell<@Nullable ? extends @Nullable String> cell) {
    // :: error: (dereference.of.nullable)
    cell.get().toString();
  }

  class Cell<E extends @Nullable Object> {
    E get() {
      throw new RuntimeException();
    }
  }
}