Rails 6.0 switches order of joined queries when combining includes and joins (causing errors)

[codeodor]

I think this is due to / related to #36834

Steps to reproduce

I used @eileencodes script from the pull request above, modified to illustrate my issue:

require "active_record"
require "minitest/autorun"
require "logger"

ActiveRecord::Base.establish_connection({ "adapter" => "mysql2", "username" => "root", "database" => "activerecord_unittest" })
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :events, force: true do |t|
    t.integer :project_id
  end

  create_table :event_details, force: true do |t|
    t.integer :event_id
  end

  create_table :projects, force: true do |t|
  end
end

class Event < ActiveRecord::Base
  has_one :event_detail
  belongs_to :project

  def self.visible_in_timeline_for
    events_for
  end

  scope :events_for, -> {
    join_project.
    join_event_detail
  }

  scope :join_project, -> {
    join_event_detail.joins(:project)
  }

  scope :join_event_detail, -> {
    joins(<<~SQL)
    INNER JOIN `event_details`
    ON `event_details`.`event_id` = `events`.`id`
    SQL
  }
end

class EventDetail < ActiveRecord::Base
  belongs_to :event
end

class Project < ActiveRecord::Base
  has_many :events
end

class BugTest < Minitest::Test
  def test_scoped_joins
    p ActiveRecord::VERSION::STRING
    # throws ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'event_details.id' in 'on clause'
    p Event.includes(:event_detail).references(:event_detail).joins("left outer join projects on projects.id = events.project_id and event_details.id = 0").where("event_details.id = 1")
  end
end

Expected behavior

The query should work as it did in Rails 5.2.3 by having the first join be the includes/references join.

Actual behavior

The query puts the includes/references join at the end, so that the joins that reference it fail.

System configuration

Rails version: 6.0.0

Ruby version: 2.5.0

cc @kamipo (as author of the related pull request)

[codeodor]

🎉