gistfile1.rb

unless File.exist?('Gemfile')                                                                                                                                                                                       
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    gem 'rails', github: 'rails/rails'
    gem 'arel', github: 'rails/arel'
    gem 'rack', github: 'rack/rack'
    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 :posts do |t|
  end

  create_table :companies do |t|
  end

  create_table :users do |t|
    t.belongs_to :company
  end

  create_table :comments do |t|
    t.belongs_to :post
    t.belongs_to :user
  end
end

class User < ActiveRecord::Base
  belongs_to :company
end

class Company < ActiveRecord::Base
  has_many :users
end

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
  belongs_to :user
end

class BugTest < Minitest::Test
  def test_association_stuff
    post = Post.create!
    company = Company.create!
    user = User.create!

    post.comments << Comment.create!(user: user)
    company.users << user

    assert_equal 1, Post.joins(:comments).where(comments: { user: company.users }).all.size
    # Passing the array works as expected:
    #assert_equal 1, Post.joins(:comments).where(comments: { user: company.users.to_a }).all.size
  end
end