ActiveRecord :has_many only partially applies a scoped :through association where the scope has #merge conditions.

invalid_query_active_record_523.rb

# frozen_string_literal: true

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"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # Activate the gem you are reporting the issue against.
  gem "activerecord", "5.2.3"
  gem "sqlite3", "~> 1.3.6"
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 :users, force: true do |t|
    t.string :name
  end

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

  create_table :registrations, force: true do |t|
    t.integer :registrant_id
  end

  create_table :session_selections, force: true do |t|
    t.integer :registration_id
    t.integer :session_id
  end
end

class User < ActiveRecord::Base
  has_many :registrations, foreign_key: :registrant_id, inverse_of: :registrant
  scope :sorted, -> { order(:name) }
end

class Session < ActiveRecord::Base
  has_many :session_selections, -> { sorted }, inverse_of: :session
  has_many :registrations, through: :session_selections
end

class SessionSelection < ActiveRecord::Base
  belongs_to :session
  belongs_to :registration
  has_one :registrant, through: :registration
  scope :sorted, -> { joins(:registrant).merge(User.sorted) }
end

class Registration < ActiveRecord::Base
  belongs_to :registrant, class_name: 'User', inverse_of: :registrations
  has_many :session_selections, dependent: :destroy
  has_many :sessions, -> { sorted }, through: :session_selections, inverse_of: :registrations
end

class BugTest < Minitest::Test
  def test_scope_with_merge_on_through
    session = Session.create!
    user = User.create!(name: 'Anson')
    registration = Registration.create!(registrant: user)
    registration.session_selections.create!(session: session)

    assert_equal 1, Session.count
    assert_equal 1, User.count
    assert_equal 1, Registration.count

    # to_sql includes 'ORDER BY "users"."name" ASC'
    # and 'INNER JOIN "users"'
    assert session.session_selections.present?

    # to_sql includes 'ORDER BY "users"."name" ASC'
    # but is missing 'INNER JOIN "users"'
    assert session.registrations.present?
  end
end