MONGOID-5790/MONGOID-5791 Fix error caused by loading a referenced class prematurely (#5839)

It's such a pleasure to delete dead code...and even more so when the
dead-code is responsible for a bug, simply by existing!

Author: jamis

lib/mongoid/touchable.rb

@@ -212,12 +212,6 @@ def touch_callback_statuses
     #
     # @return [ Symbol ] The method name.
     def define_relation_touch_method(name, association)
-      relation_classes = if association.polymorphic?
-                           association.send(:inverse_association_classes)
-                         else
-                           [ association.relation_class ]
-                         end
-
       method_name = "touch_#{name}_after_create_or_destroy"
       association.inverse_class.class_eval do
         define_method(method_name) do

spec/mongoid/association_spec.rb

@@ -15,6 +15,20 @@
     )
   end
 
+  context "when class_name references an unknown class" do
+    context "when loading" do
+      it "does not raise an exception" do
+        expect do
+          class AssocationSpecModel
+            include Mongoid::Document
+
+            embedded_in :parent, class_name: 'SomethingBogusThatDoesNotExistYet'
+          end
+        end.not_to raise_exception
+      end
+    end
+  end
+
   describe "#embedded?" do
 
     let(:person) do