rails--rails/actionpack/lib/action_view/helpers/active_model_helper.rb

require 'action_view/helpers/form_helper'
require 'active_support/core_ext/class/attribute_accessors'
require 'active_support/core_ext/enumerable'
require 'active_support/core_ext/object/blank'

module ActionView
  # = Active Model Helpers
  module Helpers
    module ActiveModelHelper
      %w(input form error_messages_for error_message_on).each do |method|
        class_eval <<-RUBY, __FILE__, __LINE__ + 1
          def #{method}(*args)
            ActiveSupport::Deprecation.warn "#{method} was removed from Rails and is now available as a plugin. " <<
              "Please install it with `rails plugin install git://github.com/rails/dynamic_form.git`.", caller
          end
        RUBY
      end
    end

    module ActiveModelFormBuilder
      %w(error_messages error_message_on).each do |method|
        class_eval <<-RUBY, __FILE__, __LINE__ + 1
          def #{method}(*args)
            ActiveSupport::Deprecation.warn "f.#{method} was removed from Rails and is now available as a plugin. " <<
              "Please install it with `rails plugin install git://github.com/rails/dynamic_form.git`.", caller
          end
        RUBY
      end
    end

    module ActiveModelInstanceTag
      def object
        @active_model_object ||= begin
          object = super
          object.respond_to?(:to_model) ? object.to_model : object
        end
      end

      %w(tag content_tag to_date_select_tag to_datetime_select_tag to_time_select_tag).each do |meth|
        module_eval "def #{meth}(*) error_wrapping(super) end", __FILE__, __LINE__
      end

      def error_wrapping(html_tag)
        if object.respond_to?(:errors) && object.errors.respond_to?(:full_messages) && object.errors[@method_name].any?
          Base.field_error_proc.call(html_tag, self)
        else
          html_tag
        end
      end

      def error_message
        object.errors[@method_name]
      end
    end

    class FormBuilder
      include ActiveModelFormBuilder
    end

    class InstanceTag
      include ActiveModelInstanceTag
    end
  end
end