message: Add arg name to "op does not support eager execution" error.
diff: @@ -480,11 +480,18 @@ string GenEagerPythonOp::Code() {
  }
  bool eager_allowed = true;
  + string ref_arg;
  for (const auto& arg : op_def_.input_arg()) {
  - if (arg.is_ref()) eager_allowed = false;
  + if (arg.is_ref()) {
  + eager_allowed = false;
  + ref_arg = arg.name();
  + }
  }
  for (const auto& arg : op_def_.output_arg()) {
  - if (arg.is_ref()) eager_allowed = false;
  + if (arg.is_ref()) {
  + eager_allowed = false;
  + ref_arg = arg.name();
  + }
  }
  if (eager_allowed) {
  @@ -497,7 +504,8 @@ string GenEagerPythonOp::Code() {
  strings::StrAppend(&result_,
  " raise RuntimeError(\n"
  " \"",
  - op_name_, " op does not support eager execution.\")\n");
  + op_name_, " op does not support eager execution. ",
  + "Arg '", ref_arg, "'' is a ref.\")\n");
  }
  if (num_outs_ > 0) {
  