AR missing join table alias

test_ar.rb

unless File.exist?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    gem 'rails', github: 'rails/rails'
    gem 'arel', github: 'rails/arel'
    gem 'sqlite3'
  GEMFILE

  system 'bundle install'
end

require 'bundler'
Bundler.setup(:default)

require 'active_record'
require 'minitest/autorun'
require 'logger'

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :orders do |t|
  end

  create_table :deliveries do |t|
  end

  create_table :users do |t|
  end

  create_table :bookings do |t|
    t.integer  "user_id",                               null: false
    t.integer  "bookable_id"
    t.string   "bookable_type"
    t.integer  "booking_id"
  end

end

class User < ActiveRecord::Base
  has_many  :bookings
  has_many  :orders,      through: :bookings, source: :bookable, source_type: "Order"
  has_many  :deliveries,  through: :bookings, source: :bookable, source_type: "Delivery"

  scope :with_order, -> { joins(:orders).where(id: 1) }
  scope :with_delivery, -> { joins(:deliveries).where(id: 1) }

  scope :with_bookables, -> { with_order.with_delivery }
end

class Booking < ActiveRecord::Base
  belongs_to :bookable, polymorphic: true
end

class Order < ActiveRecord::Base
  has_one :booking, as: :bookable
end

class Delivery < ActiveRecord::Base
  has_one :booking, as: :bookable
end

class BugTest < Minitest::Test
  def test_polymorphic_join_conditions
    user = User.create
    user.deliveries.create
    user.orders.create

    assert_equal 1, User.with_order.count
    assert_equal 1, User.with_delivery.count
    assert_equal 1, User.with_bookables.count
  end
end