Inherit decorator from superclass.

If the class itself does not have a decorator, try the superclass.

lib/draper/decoratable.rb

@@ -75,8 +75,12 @@ module Draper
         decorator_name = "#{prefix}Decorator"
         decorator_name.constantize
       rescue NameError => error
-        raise unless error.missing_name?(decorator_name)
-        raise Draper::UninferrableDecoratorError.new(self)
+        if superclass.respond_to?(:decorator_class)
+          superclass.decorator_class
+        else
+          raise unless error.missing_name?(decorator_name)
+          raise Draper::UninferrableDecoratorError.new(self)
+        end
       end
 
       # Compares with possibly-decorated objects.

spec/draper/decoratable_spec.rb

@@ -152,6 +152,12 @@ module Draper
         it "infers the decorator from the class" do
           expect(Product.decorator_class).to be ProductDecorator
         end
+
+        context "without a decorator on its own" do
+          it "infers the decorator from a superclass" do
+            expect(SpecialProduct.decorator_class).to be ProductDecorator
+          end
+        end
       end
 
       context "for ActiveModel classes" do

spec/spec_helper.rb

@@ -13,6 +13,7 @@ end
 class Model; include Draper::Decoratable; end
 
 class Product < Model; end
+class SpecialProduct < Product; end
 class ProductDecorator < Draper::Decorator; end
 class ProductsDecorator < Draper::CollectionDecorator; end