// `proto` should point to a sequence of bytes of length `proto_len`
// representing a binary serialization of an AttrValue protocol
// buffer.
TF_CAPI_EXPORT extern void TF_SetAttrValueProto(TF_OperationDescription* desc,
                                                const char* attr_name,
                                                const void* proto,

    tensorflow::AttrValue attr;
    for (const string& v : list) {
      attr.mutable_list()->add_s(v);
    }
    string bytes;
    attr.SerializeToString(&bytes);
    TF_SetAttrValueProto(desc, tensorflow::kColocationAttrName, bytes.data(),
                         bytes.size(), s_);
    ASSERT_EQ(TF_OK, TF_GetCode(s_)) << TF_Message(s_);
  }

  void VerifyCollocation(TF_Operation* op,