checker/tests/tainting/Issue3033.java

import org.checkerframework.checker.tainting.qual.Tainted;
import org.checkerframework.checker.tainting.qual.Untainted;

public class Issue3033 {

  void main() {
    @Tainted String a = getTainted();
    // :: warning: (instanceof.unsafe)
    if (a instanceof @Untainted String) {
      // `a` is now refined to @Untainted String
      isUntainted(a);
    }
  }

  static void isUntainted(@Untainted String a) {}

  static @Tainted String getTainted() {
    return "hi";
  }
}