errors_with_symbol.rb

require 'active_model'

class ActiveModel::Errors

  module WithSymbol
    attr_accessor :symbol_value
  end

  def add_with_symbol(attribute, message = :invalid, options = {})
    add_without_symbol(attribute, message, options).tap do |messages|
      normalized_message = messages.last
      normalized_message.extend WithSymbol

      if message.is_a? Symbol
        normalized_message.symbol_value = message
      end
    end
  end
  alias_method_chain :add, :symbol

  def symbolized_messages
    list = messages.map do |attribute, messages|
      [attribute, messages.map(&:symbol_value)]
    end

    Hash[list]
  end
end