Gotcha with STI and unscoped queries against the base class

unscoped_gotcha_test.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'
  gem 'rails', github: 'rails/rails'
  gem 'arel', github: 'rails/arel'
  gem 'rack', github: 'rack/rack'
  gem 'sprockets', github: 'rails/sprockets'
  gem 'sprockets-rails', github: 'rails/sprockets-rails'
  gem 'sass-rails', github: 'rails/sass-rails'
  gem 'sqlite3'
end

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

# 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 :posts, force: true  do |t|
    t.string :type
    t.timestamps
  end
end

class Post < ActiveRecord::Base
  def self.find_and_modify(pid)
    p = Post.find(pid)
    p.touch
    p.save!
  end
end

class SubPost < Post
  after_save :query_subclass

  def query_subclass
    query_sql = SubPost.all.to_sql
    unless query_sql.include?(%|"posts"."type" IN ('SubPost')|)
      raise "Expected query to scope by type: #{query_sql}"
    end
  end
end

class BugTest < Minitest::Test
  def setup
    @sub = SubPost.create!
  end

  # Passes under Rails master
  def test_query_in_same_frame_should_use_sti_where_clause
    p = Post.unscoped.find(@sub.id)
    p.touch
    p.save!
  end

  # FAILS under Rails master
  def test_query_in_subframe_should_use_sti_where_clause
    Post.unscoped.find_and_modify(@sub.id)
  end
end