no_previous_changes_on_autosave.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 'activerecord', '5.1'
  gem 'pry'
  gem 'sqlite3'
end

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

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# 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 :parents, force: true do |t|
    t.string :name
  end

  create_table :children, force: true do |t|
    t.string :name
    t.integer :parent_id
  end
end

class Parent < ActiveRecord::Base
  has_one :child, :inverse_of => :parent, :autosave => true

  @@foo = 0

  after_validation :foo

  def foo
    @@foo += 1
  end
end

class Child < ActiveRecord::Base
  belongs_to :parent, :inverse_of => :child, :autosave => true
end

class BugTest < Minitest::Test
  def setup
    @parent = Parent.create!(name: 'P')

    @child = Child.new(name: 'Hi!')
    @child.parent = @parent
    @child.save!
  end


  # The case below fail, because
  # https://github.com/rails/rails/blob/v4.2.7.1/activerecord/lib/active_record/autosave_association.rb#L441
  # there `record.changed_for_autosave?` is true through it's not changed.
  # It's true because `child` is changed.
  # Therefore child is being saved in the wrong place, then saved one more time
  # where it should be saved and as a result we see that `child.previous_changes` is {}
  def test_prev_changes
    assert_equal [nil, "Hi!"], @child.previous_changes[:name]
  end

  # This case pass because of another thing
  # https://github.com/rails/rails/blob/v4.2.7.1/activerecord/lib/active_record/autosave_association.rb#L432
  # association there is nil. But if I put debugger there and eval `parent` manually it would work
  # as the third case.
  def test_prev_changes_pass
    child2 = Child.create!(name: '2', parent_id: @parent.id)
    assert_equal [nil, "2"], child2.previous_changes[:name]
  end

  # This also fail for the same reason as test_prev_changes
  def test_prev_changes2
    child3 = Child.create!(name: '3', parent: @parent)
    assert_equal [nil, "3"], child3.previous_changes[:name]
  end

  # This case fails because of similar behaviour in different place
  def test_after_validation
    @parent.class.class_variable_set('@@foo', 0)
    @parent.update!(name: 'pp')
    assert_equal 1, @parent.class.class_variable_get('@@foo')
  end
end