Failing tests for Rails 4 unscoped when used with eager loading (includes). Two assertions should fail: Line 88 and Line 110. Line 88 should pass in Rails 3, but won't in Rails 4. Line 110 leverages the 'unscoped association' added in Rails 4, but still fails.

rails4_unscoped_tests.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'
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 :checklists do |t|
    t.integer :tenant_id
  end

  create_table :submissions do |t|
    t.integer :checklist_id
    t.integer :tenant_id
  end
  
  create_table :tenants do |t|
  end
end

class Checklist < ActiveRecord::Base
  default_scope { where(tenant_id: Tenant.current_id) }

  has_many :submissions
  belongs_to :tenant
end

class Submission < ActiveRecord::Base
  default_scope { where(tenant_id: Tenant.current_id) }
  
  belongs_to :checklist
  ###### This unscoped association is my workaround in Rails 4 
  ###### You'll want comment out if testing in Rails 3
  belongs_to :unscoped_checklist, -> { unscope(where: :tenant_id) }, foreign_key: :checklist_id, class_name: "Checklist"
  belongs_to :tenant
end

class Tenant < ActiveRecord::Base
  cattr_accessor :current_id
  
  has_many :checklists
  has_many :submissions
end

class BugTest < Minitest::Test
  def test_association_stuff
    tenant = Tenant.create!
    checklist = Checklist.create!(tenant_id: tenant.id)
    submission = Submission.create!(tenant_id: tenant.id, checklist_id: checklist.id)
    s = nil
    c = nil

    Tenant.current_id = tenant.id  

    assert_equal 1, Submission.count
    assert_equal 1, Checklist.count
    assert_equal 1, Checklist.first.submissions.count
    assert_equal checklist.id, Submission.first.checklist.id
    
    Tenant.current_id = nil

    assert_equal 0, Checklist.count
    assert_equal 0, Submission.count
    assert_equal 1, Checklist.unscoped.count
    assert_equal 1, Submission.unscoped.count
    
    ####### Should find submission and preload its checklist
    Submission.unscoped { Checklist.unscoped { s = Submission.includes(:checklist).find(submission.id) }}
    assert_equal submission.id, s.id
    
    ####### I believe this will pass in Rails 3.2.17, but fail in Rails 4 (undefined method 'id' for nil object)
    assert_equal checklist.id, s.checklist.id
    
    ####### Everything below this line is Rails 4 specific 
    ####### (relates to unscoped_checklist association on Submission class)

    s = Submission.unscoped.find(submission.id)
    assert_equal submission.id, s.id
    ####### This works...
    assert_equal checklist.id, s.unscoped_checklist.id
    
    ####### This works (using an unscoped block explicitly)
    s = Submission.unscoped.find(submission.id)
    assert_equal submission.id, s.id
    Checklist.unscoped do
      c = s.checklist
    end
    assert_equal checklist.id, c.id
    
    s = Submission.unscoped.includes(:unscoped_checklist).find(submission.id)
    assert_equal submission.id, s.id
    ###### This doesn't... The 'unscoped' call actually defeats the preloaded unscoped association
    ###### The default_scope for the Checklist class is applied even though it's specifically
    ###### overriden in this assocation.
    ###### Also fails with 'preload'
    assert_equal checklist.id, s.unscoped_checklist.id
  end
end