message: ocaml: Improve error when an invalid source is used.
diff: @@ -133,6 +133,8 @@ drake.Node.extensions['cmi'] = InterfaceObject
  def _to_objects(node, toolkit, config):
  if isinstance(node, Object):
  return [node]
  + elif not isinstance(node, Node):
  + raise Exception('non-OCaml source for an OCaml binary: {}'.format(node))
  else:
  return _flatten(_to_objects(o, toolkit, config) for o in node.to_objects(toolkit, config))
  