Ensure custom PK types are casted in through reflection queries

Make sure primary keys with non-integer types can be correctly type
casted in through reflections.

activerecord/CHANGELOG.md

+*   Ensure custom PK types are casted in through reflection queries.
+
+    *Gannon McGibbon*
+
 *   Preserve user supplied joins order as much as possible.
 
     Fixes #36761, #34328, #24281, #12953.

activerecord/lib/active_record/reflection.rb

@@ -764,7 +764,16 @@ def through_reflection?
       end
 
       def klass
-        @klass ||= delegate_reflection.compute_class(class_name)
+        @klass ||= delegate_reflection.compute_class(class_name).tap do |klass|
+          if !parent_reflection.is_a?(HasAndBelongsToManyReflection) &&
+             !klass.reflections.include?(options[:through].to_s) &&
+             active_record.type_for_attribute(active_record.primary_key).type != :integer
+            raise NotImplementedError, <<~MSG.squish
+              In order to correctly type cast #{active_record}.#{active_record.primary_key},
+              #{klass} needs to define a :#{options[:through]} association.
+            MSG
+          end
+        end
       end
 
       # Returns the source of the through reflection. It checks both a singularized

activerecord/test/cases/reflection_test.rb

@@ -256,6 +256,14 @@ def test_has_many_through_reflection
     assert_kind_of ThroughReflection, Subscriber.reflect_on_association(:books)
   end
 
+  def test_uncastable_has_many_through_reflection
+    error = assert_raises(NotImplementedError) { Subscriber.new.published_books }
+    assert_equal <<~MSG.squish, error.message
+      In order to correctly type cast Subscriber.nick,
+      PublishedBook needs to define a :subscriptions association.
+    MSG
+  end
+
   def test_chain
     expected = [
       Organization.reflect_on_association(:author_essay_categories),

activerecord/test/models/dashboard.rb

@@ -2,4 +2,6 @@
 
 class Dashboard < ActiveRecord::Base
   self.primary_key = :dashboard_id
+
+  has_one :speedometer
 end

activerecord/test/models/subscriber.rb

@@ -4,6 +4,7 @@ class Subscriber < ActiveRecord::Base
   self.primary_key = "nick"
   has_many :subscriptions
   has_many :books, through: :subscriptions
+  has_many :published_books, through: :subscriptions
 end
 
 class SpecialSubscriber < Subscriber

activerecord/test/models/subscription.rb

@@ -2,6 +2,7 @@
 
 class Subscription < ActiveRecord::Base
   belongs_to :subscriber, counter_cache: :books_count
+  belongs_to :published_book
   belongs_to :book
 
   validates_presence_of :subscriber_id, :book_id