checker/tests/nullness/UnusedNullness.java

import java.lang.annotation.ElementType;
import java.lang.annotation.Target;
import org.checkerframework.checker.nullness.qual.*;
import org.checkerframework.framework.qual.SubtypeOf;
import org.checkerframework.framework.qual.Unused;

// TODO: feature request: the Nullness Checker should be aware of the @Unused annotation.
// This is difficult to implement: one needs to determine the correct AnnotatedTypeFactory for the
// "when" type system and use it to determine the right annotated type. We currently don't have a
// mechanism to do this.
//
// @skip-test
public class UnusedNullness {

  @SubtypeOf({})
  @Target(ElementType.TYPE_USE)
  public @interface Prototype {}

  @Unused(when = Prototype.class)
  public Object ppt;

  protected @Prototype UnusedNullness() {
    // It should be legal to initialize an unused field to null in
    // a constructor with @Prototype receiver.
    this.ppt = null;
  }

  protected @Prototype UnusedNullness(int disambiguate_overloading) {
    // It should be legal to NOT initialize an unused field in
    // a constructor with @Prototype receiver.
  }

  protected void protometh(@Prototype UnusedNullness this) {
    // It should be legal to initialize the unused field to null in
    // a method with @Prototype receiver.
    this.ppt = null;
  }

  protected void meth() {
    // Otherwise it's not legal.
    // :: error: (assignment)
    this.ppt = null;
  }

  protected void useUnusedField1(@Prototype UnusedNullness this) {
    // :: error: (assignment)
    @NonNull Object x = this.ppt;
  }

  protected void useUnusedField2() {
    @NonNull Object x = this.ppt;
  }
}