Pluck relations is casting values for the wrong model

[manu-d]

Steps to reproduce

When plucking an associated model attributes, Active record is casting values based on the original model attributes types, instead of the associated one

Test example

Simply save this file test_pluck.rb, and run ruby test_pluck.rb

# frozen_string_literal: true

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"

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

  # Activate the gem you are reporting the issue against.
  gem "activerecord", "5.2.0"
  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 :posts, force: :true do |t|
    t.string :content
    t.string :author_id
  end

  create_table :authors, id: :string, force: :true do |t|
    t.string :name
  end
end

class Post < ActiveRecord::Base
  belongs_to :author
end

class Author < ActiveRecord::Base
end

class BugTest < Minitest::Test
  def test_relation_pluck
    author = Author.create!(id: "Author 1", name: "Maupassant")
    post = Post.create!(content: "Horla", author: author)
    relation = Post.includes(:author)
    assert_equal [author.name], relation.pluck(Arel.sql("authors.name"))
    assert_equal [author.id], relation.pluck(Arel.sql("authors.id"))
  end
end

Actual behavior

We can see that the first test works. However, the second one fails.
It seems that here, for klass.attributes_types, we are sending the attributes types of Post, instead of Author. Since Post has an Integer id, the Author id will be cast to an integer.
Therefore, 'Author 1'.to_i will return 0.
(If you change the id Author 1 to 1 Author, '1 Author'.to_i = 1, so it will return 1)
SQL request is correct, and returning the correct value. The casting to int is breaking it.

System configuration

Rails version: 5.2.0

Ruby version: 2.4.1

[manu-d]

(Test case fails with any active record version > 4)

[rails-bot]

This issue has been automatically marked as stale because it has not been commented on for at least three months.
The resources of the Rails team are limited, and so we are asking for your help.
If you can still reproduce this error on the 5-2-stable branch or on master, please reply with all of the information you have about it in order to keep the issue open.
Thank you for all your contributions.