`ActiveRecord::Persistence#becomes` does not clone eager-loading state and can raise Strict Loading violations about rails

[stevepolitodesign]

Also noting that calling includes on the class passed to becomes does not work either:

assert_equal [comment], post.becomes(Post.includes(:comments)).comments # <= This line fails

[stevepolitodesign]

The inverse also applies. If we enable strict loading on a query, post.becomes(Post).comments will not raise.

# frozen_string_literal: true

require "bundler/inline"

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

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

  gem "rails", github: "rails/rails", branch: "main"

  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|
  end

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

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
end

class BugTest < Minitest::Test
  def test_becomes_eager_loading
    comment = Comment.new

    Post.create! comments: [comment]
    post = Post.strict_loading.last!

    assert_equal [comment], post.becomes(Post).comments # <= This line passes
    assert_equal [comment], post.comments # <= This line fails
  end
end