module Protobuf::Descriptor

def self.id2label(label_id)
  require 'protobuf/descriptor/descriptor_proto'
  case label_id
  when Google::Protobuf::FieldDescriptorProto::Label::LABEL_REQUIRED then
    :required
  when Google::Protobuf::FieldDescriptorProto::Label::LABEL_OPTIONAL then
    :optional
  when Google::Protobuf::FieldDescriptorProto::Label::LABEL_REPEATED then
    :repeated
  else
    raise ArgumentError, "Invalid label: #{proto.label}"
  end
end