Regression in Rails 5.0.0.beta3

test_polymorphic_validates_associated.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', '5.0.0.beta3' # CHANGE TO '5.0.0.beta2' for tests to pass
  gem 'sqlite3'
  gem 'pry-nav'
end

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 :accounts, force: true do |t|
  end

  create_table :authorizations, force: true do |t|
    t.integer  :authority_id, null: false
    t.string   :authority_type, null: false
  end
end

class Account < ActiveRecord::Base
end

class Authorization < ActiveRecord::Base
  validates :authority_id, :authority_type, presence: true
  belongs_to :authority, polymorphic: true
end

class Partnership < Authorization
  validates_associated :authority
end

class BugTest < Minitest::Test
  def test_polymorphic_validates_associated
    ActiveRecord::Base.belongs_to_required_by_default = true

    account = Account.create!
    account = Account.create!
    authority = Authorization.create! authority: account
    partnership = Partnership.new authority: authority

    Authorization.belongs_to :partner, foreign_key: 'authority_id', class_name: 'Authorization'

    assert partnership.valid?, partnership.errors.full_messages.to_sentence
    # on Rails 5.0.0.beta2:
    # => No errors

    # on Rails 5.0.0.beta3 (and master@364e155):
    # => Failure: Authority is invalid

  end
end