Pretend to be instance_of?(source.class)

lib/draper/decorator.rb

@@ -29,7 +29,7 @@ def initialize(source, options = {})
       source.to_a if source.respond_to?(:to_a) # forces evaluation of a lazy query from AR
       @source = source
       @context = options.fetch(:context, {})
-      handle_multiple_decoration(options) if source.is_a?(Draper::Decorator)
+      handle_multiple_decoration(options) if source.instance_of?(self.class)
     end
 
     class << self
@@ -188,13 +188,21 @@ def ==(other)
       source == (other.respond_to?(:source) ? other.source : other)
     end
 
-    # @overload kind_of?(class)
-    #   Checks if `self.kind_of?(class)` or `source.kind_of?(class)`
+    # Checks if `self.kind_of?(klass)` or `source.kind_of?(klass)`
+    #
+    # @param [Class] klass
     def kind_of?(klass)
       super || source.kind_of?(klass)
     end
     alias_method :is_a?, :kind_of?
 
+    # Checks if `self.instance_of?(klass)` or `source.instance_of?(klass)`
+    #
+    # @param [Class] klass
+    def instance_of?(klass)
+      super || source.instance_of?(klass)
+    end
+
     # Delegated to the source object, in case it is `nil`.
     def present?
       source.present?
@@ -304,10 +312,10 @@ def self.allow?(method)
     end
 
     def handle_multiple_decoration(options)
-      if source.instance_of?(self.class)
+      if source.applied_decorators.last == self.class
         @context = source.context unless options.has_key?(:context)
         @source = source.source
-      elsif source.decorated_with?(self.class)
+      else
         warn "Reapplying #{self.class} decorator to target that is already decorated with it. Call stack:\n#{caller(1).join("\n")}"
       end
     end

spec/draper/decorator_spec.rb

@@ -49,21 +49,29 @@
       end
     end
 
-    it "decorates other decorators" do
-      decorator = ProductDecorator.new(source)
-      SpecificProductDecorator.new(decorator).source.should be decorator
-    end
+    context "when decorating other decorators" do
+      it "redecorates" do
+        decorator = ProductDecorator.new(source)
+        SpecificProductDecorator.new(decorator).source.should be decorator
+      end
 
-    it "warns if target is already decorated with the same decorator class" do
-      warning_message = nil
-      Object.any_instance.stub(:warn) { |message| warning_message = message }
+      context "when the same decorator has been applied earlier in the chain" do
+        let(:decorator) { SpecificProductDecorator.new(ProductDecorator.new(Product.new)) }
+
+        it "warns" do
+          warning_message = nil
+          Object.any_instance.stub(:warn) {|message| warning_message = message }
+
+          expect{ProductDecorator.new(decorator)}.to change{warning_message}
+          warning_message.should =~ /ProductDecorator/
+          warning_message.should include caller(1).first
+        end
 
-      deep_decorator = SpecificProductDecorator.new(ProductDecorator.new(Product.new))
-      expect {
-        ProductDecorator.new(deep_decorator)
-      }.to change { warning_message }
-      warning_message.should =~ /ProductDecorator/
-      warning_message.should include caller(1).first
+        it "redecorates" do
+          Object.any_instance.stub(:warn)
+          ProductDecorator.new(decorator).source.should be decorator
+        end
+      end
     end
   end
 
@@ -696,6 +704,14 @@
     subject.is_a?(subject.class).should be_true
   end
 
+  it "pretends to be an instance of the source class" do
+    subject.instance_of?(source.class).should be_true
+  end
+
+  it "is still an instance of its own class" do
+    subject.instance_of?(subject.class).should be_true
+  end
+
   describe ".decorates_finders" do
     it "extends the Finders module" do
       ProductDecorator.should be_a_kind_of Draper::Finders

spec/dummy/spec/models/post_spec.rb

@@ -6,7 +6,6 @@
     subject { Post.first }
 
     it "is true for other instances' decorators" do
-      pending if Rails.version.start_with?("3.0")
       other = Post.first
       subject.should_not be other
       (subject == other.decorate).should be_true