private ImmutableSet<TypeElement> getSupportedAnnotationTypeElements() {
    checkState(steps != null);
    return steps.stream()
        .flatMap(step -> getSupportedAnnotationTypeElements(step).stream())
        .collect(toImmutableSet());
  }
An optional hook for logic to be executed at the end of each round.
common/src/main/java/com/google/auto/common/BasicAnnotationProcessor.java