Deduplicate joins values

[kamipo]

#36805 have one possible regression that failing deduplication if
joins_values have complex order (e.g. joins_values = [join_node_a, :comments, :tags, join_node_a]).

This fixes the deduplication to take it in the first phase before
grouping.

I believe the deduplication issue #36805 (comment) might be fixed by this.

cc @eileencodes

[eileencodes]

Going to test this out, I literally just got a reproduction script working 😆

[eileencodes]

Yes! This fixes it thank you!

For posterity here's the script I got working:

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

ActiveRecord::Base.establish_connection({ "adapter" => "mysql2", "username" => "rails", "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
    # throws a ActiveRecord::StatementInvalid: Mysql2::Error: Not unique table/alias: 'event_details'
    p Event.visible_in_timeline_for
  end
end

[kamipo]

❤️ Backported 97f1fef.