rails--rails/activemodel/lib/active_model/validations/confirmation.rb

module ActiveModel

  # == Active Model Confirmation Validator
  module Validations
    class ConfirmationValidator < EachValidator #:nodoc:
      def validate_each(record, attribute, value)
        if (confirmed = record.send("#{attribute}_confirmation")) && (value != confirmed)
          human_attribute_name = record.class.human_attribute_name(attribute)
          record.errors.add(:"#{attribute}_confirmation", :confirmation, options.merge(:attribute => human_attribute_name))
        end
      end

      def setup(klass)
        klass.send(:attr_accessor, *attributes.map do |attribute|
          :"#{attribute}_confirmation" unless klass.method_defined?(:"#{attribute}_confirmation")
        end.compact)
      end
    end

    module HelperMethods
      # Encapsulates the pattern of wanting to validate a password or email
      # address field with a confirmation.
      #
      #   Model:
      #     class Person < ActiveRecord::Base
      #       validates_confirmation_of :user_name, :password
      #       validates_confirmation_of :email_address,
      #                                 message: 'should match confirmation'
      #     end
      #
      #   View:
      #     <%= password_field "person", "password" %>
      #     <%= password_field "person", "password_confirmation" %>
      #
      # The added +password_confirmation+ attribute is virtual; it exists only
      # as an in-memory attribute for validating the password. To achieve this,
      # the validation adds accessors to the model for the confirmation
      # attribute.
      #
      # NOTE: This check is performed only if +password_confirmation+ is not
      # +nil+. To require confirmation, make sure to add a presence check for
      # the confirmation attribute:
      #
      #   validates_presence_of :password_confirmation, if: :password_changed?
      #
      # Configuration options:
      # * <tt>:message</tt> - A custom error message (default is: "doesn't match
      #   confirmation").
      #
      # There is also a list of default options supported by every validator:
      # +:if+, +:unless+, +:on+ and +:strict+.
      # See <tt>ActiveModel::Validation#validates</tt> for more information
      def validates_confirmation_of(*attr_names)
        validates_with ConfirmationValidator, _merge_attributes(attr_names)
      end
    end
  end
end