Reproduction of a possible bug in ActiveRecord_AssociationRelation#or

ActiveRecordRelation#or.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"
  # Activate the gem you are reporting the issue against.
  gem "activerecord", "5.1.0"
  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 :users, force: true do |t|
  end

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

  create_table :user_publications, force: true do |t|
    t.integer :user_id
    t.integer :publication_id
  end

  create_table :comments, force: true do |t|
    t.integer :publication_id
    t.integer :user_id
  end
end

class User < ActiveRecord::Base
  has_many :user_publications
  has_many :publications, through: :user_publications
  has_many :comments
end

class Publication < ActiveRecord::Base  
  has_many :user_publications
  has_many :users, through: :user_publications
  has_many :comments
end

class UserPublication < ActiveRecord::Base
  belongs_to :user
  belongs_to :publication
end

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

class BugTest < Minitest::Test
  def test_association_stuff
    user = User.create!
    publication1 = Publication.create!
    publication2 = Publication.create!
    publication3 = Publication.create!

    user.publications << publication1
    user.publications << publication2
    user.publications << publication3
    
    publication1.comments << Comment.create!
    publication2.comments << Comment.create!
    publication3.comments << Comment.create!

    relevant_comments_relation = Comment.none
    relevant_comments_array = []
    user.publications.each do |publication|
      relevant_comments_relation = relevant_comments_relation.or(publication.comments)
      relevant_comments_array = relevant_comments_array + publication.comments
    end

    assert_equal relevant_comments_array, relevant_comments_relation
    assert_equal relevant_comments_array.last, relevant_comments_relation.last
    assert_equal relevant_comments_array.last.publication, relevant_comments_relation.last.publication
  end
end