When decoration fails, show original class

lib/draper/decoratable.rb

@@ -69,16 +69,16 @@ def decorator_class?
       # `Product` maps to `ProductDecorator`).
       #
       # @return [Class] the inferred decorator class.
-      def decorator_class
+      def decorator_class(called_on = self)
         prefix = respond_to?(:model_name) ? model_name : name
         decorator_name = "#{prefix}Decorator"
         decorator_name_constant = decorator_name.safe_constantize
         return decorator_name_constant unless decorator_name_constant.nil?
 
         if superclass.respond_to?(:decorator_class)
-          superclass.decorator_class
+          superclass.decorator_class(called_on)
         else
-          raise Draper::UninferrableDecoratorError.new(self)
+          raise Draper::UninferrableDecoratorError.new(called_on)
         end
       end
 

spec/draper/decoratable_spec.rb

@@ -73,6 +73,16 @@ module Draper
         expect(Product).to receive(:decorator_class).and_return(:some_decorator)
         expect(product.decorator_class).to be :some_decorator
       end
+
+      it "specifies the class that #decorator_class was first called on (superclass)" do
+        person = Person.new
+        expect { person.decorator_class }.to raise_error(Draper::UninferrableDecoratorError, 'Could not infer a decorator for Person.')
+      end
+
+      it "specifies the class that #decorator_class was first called on (subclass)" do
+        child = Child.new
+        expect { child.decorator_class }.to raise_error(Draper::UninferrableDecoratorError, 'Could not infer a decorator for Child.')
+      end
     end
 
     describe "#==" do

spec/spec_helper.rb

@@ -16,6 +16,8 @@ class Model; include Draper::Decoratable; end
 class Product < Model; end
 class SpecialProduct < Product; end
 class Other < Model; end
+class Person < Model; end
+class Child < Person; end
 class ProductDecorator < Draper::Decorator; end
 class ProductsDecorator < Draper::CollectionDecorator; end