code: public void markParentClasses(TypeElement type) {
      while (type != null) {
        String typeID = ElementReferenceMapper.stitchClassIdentifier(type, env.elementUtil());
        ReferenceNode node = elementReferenceMap.get(typeID);
        if (node == null) {
          ErrorUtil.warning("Encountered .class parent class while accessing: " + typeID);
          return;
        }
        if (node.reachable) {
          return;
        }
        node.reachable = true;
        if (ElementUtil.isStatic(type)) {
          return;
        }
        type = ElementUtil.getDeclaringClass(type);
      }
    }
docs: Mark all ancestor classes of (sub)class as used