Preload polymorphic association with scope

bug.rb

# frozen_string_literal: true

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"
  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "sqlite3"
  gem 'activerecord', github: 'rails/rails', ref: ENV['REF']
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 :pictures, force: true do |t|
    t.references :imageable, polymorphic: true
  end

  create_table :employees, force: true do |t|
    t.string :name
    t.boolean :active, default: 1
  end
end


class Picture < ActiveRecord::Base
  belongs_to :imageable, -> { where(active: true) }, polymorphic: true
end

class Employee < ActiveRecord::Base
  has_many :pictures, as: :imageable
end

class BugTest < Minitest::Test
  def test_preload_polymorphic_association
    employee = Employee.create!(name: 'John')
    picture = Picture.create!(imageable: employee)
    picture.association(:imageable).reset # Reset the association, otherwise `.preload` will return a `AlreadyLoaded` association

    Picture.preload(:imageable).first
  end
end

Previous behaviour = REF=3523516fab1172be195c72d3280ef582fc0ea1a7 bundle exec ruby bug.rb
Current behaviour = REF=489df7e bundle exec ruby bug.rb