* is determined heuristically by class name (see {@link ClassInfo#isTopLevel}).
   */
  public ImmutableSet<ClassInfo> getTopLevelClasses() {
    return FluentIterable.from(resources)
        .filter(ClassInfo.class)
        .filter(ClassInfo::isTopLevel)
        .toSet();
  }

  /** Returns all top level classes whose package name is {@code packageName}. */