bug.rb

unless File.exists?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    gem 'rails', github: 'rails/rails'
    gem 'sqlite3'
    gem 'debugger'
  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 :accounts do |t|
  end

  create_table :permissions do |t|
    t.references :accessible, polymorphic: true
    t.references :permissible, polymorphic: true
  end

  create_table :users do |t|
  end

end

class Account < ActiveRecord::Base
  has_many :permissions, as: :permissible
  has_many :users, through: :permissions, source: :accessible, source_type: 'User'
end

class Permission < ActiveRecord::Base
  belongs_to :accessible, polymorphic: true
  belongs_to :permissible, polymorphic: true
end

class User < ActiveRecord::Base
  has_many :permissions, as: :accessible
  has_many :accounts, through: :permissions, source: :permissible, source_type: 'Account'
  validates_presence_of :accounts
end

class BugTest < MiniTest::Unit::TestCase
  def test_association_stuff
    User.delete_all
    Account.delete_all
    account = Account.create!
    account.users.create!
  end
end