private void checkForTypeHierarchy(Protoclass protoclass, ValueType type) {
    scanAndReportInvalidInheritance(protoclass, type.element, type.extendedClasses());
    scanAndReportInvalidInheritance(protoclass, type.element, type.implementedInterfaces());
  }
It may grow later in some better abstraction, but as it stands now, currently it is
just a glue between new "protoclass" model and old discovery routines.
value-processor/src/org/immutables/value/processor/meta/ValueTypeComposer.java