AR bug repro

repro.rb

# frozen_string_literal: true

require 'bundler/inline'

gemfile(true) do
  source 'https://rubygems.org'

  gem 'rails', '=6.1.5.1'
  gem 'sqlite3'
end

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

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define { create_table(:foos, force: true) }
Foo = Class.new(ActiveRecord::Base)

class BugTest < Minitest::Test
  def test_association_stuff
    5.times { Foo.create }
    assert_equal [3], Foo.where(id: [1,2,3]).merge(Foo.where(id: [3,4,5])).pluck(:id)
  end
end