Adds support for ActiveModel::Errors

The goal here is to improve ActiveModel support so that Draper can
work seamlessly with Rails' FormHelpers, proxying the model's #errors
method.

I also added support for ActiveModel::Errors, adding a proxy to the
model's #errors method only if it's a descendant of
ActiveModel::Validations.

Also some refactoring was done. Draper now proxies #to_param and #id
methods only if the model is an ActiveModel descendant.

Other things I did include:

- created Draper::ActiveModelSupport::Proxies, which contains the
  methods for proxying default methods(to_param, id, etc) depending
on the ancestors
- wrote specs for class with ActiveModel as ancestor
- wrote specs for class without ActiveModel as ancestor

lib/draper.rb

@@ -1,5 +1,6 @@
 require "draper/version"
 require 'draper/system'
+require 'draper/active_model_support'
 require 'draper/base'
 require 'draper/lazy_helpers'
 require 'draper/model_support'

lib/draper/active_model_support.rb

@@ -0,0 +1,24 @@
+module Draper::ActiveModelSupport
+  module Proxies
+    def create_proxies
+      # These methods (as keys) will be created only if the correspondent
+      # model descends from a specific class (as value)
+      proxies = {}
+      proxies[:to_param] = ActiveModel::Conversion if defined?(ActiveModel::Conversion)
+      proxies[:errors]   = ActiveModel::Validations if defined?(ActiveModel::Validations)
+      proxies[:id]       = ActiveRecord::Base if defined?(ActiveRecord::Base)
+
+      proxies.each do |method_name, dependency|
+        if model.kind_of?(dependency) || dependency.nil?
+          class << self
+            self
+          end.class_eval do
+            self.send(:define_method, method_name) do |*args, &block|
+              model.send(method_name, *args, &block)
+            end
+          end
+        end
+      end
+    end
+  end
+end

lib/draper/base.rb

@@ -8,15 +8,11 @@ module Draper
 
     DEFAULT_DENIED = Object.instance_methods << :method_missing
     DEFAULT_ALLOWED = []
-    FORCED_PROXY = [:to_param, :id]
-    FORCED_PROXY.each do |method|
-      define_method method do |*args, &block|
-        model.send method, *args, &block
-      end
-    end
     self.denied = DEFAULT_DENIED
     self.allowed = DEFAULT_ALLOWED
 
+    include Draper::ActiveModelSupport::Proxies
+
     # Initialize a new decorator instance by passing in
     # an instance of the source class. Pass in an optional
     # context inside the options hash is stored for later use.
@@ -28,6 +24,7 @@ module Draper
       self.class.model_class = input.class if model_class.nil?
       @model = input.kind_of?(Draper::Base) ? input.model : input
       self.options = options
+      create_proxies
     end
 
     # Proxies to the class specified by `decorates` to automatically
@@ -260,7 +257,7 @@ module Draper
   private
 
     def allow?(method)
-      (allowed.empty? || allowed.include?(method) || FORCED_PROXY.include?(method)) && !denied.include?(method)
+      (allowed.empty? || allowed.include?(method)) && !denied.include?(method)
     end
 
     def find_association_reflection(association)

spec/draper/base_spec.rb

@@ -4,6 +4,7 @@ describe Draper::Base do
   before(:each){ ApplicationController.new.set_current_view_context }
   subject{ Decorator.new(source) }
   let(:source){ Product.new }
+  let(:non_active_model_source){ NonActiveModelProduct.new }
 
   context("proxying class methods") do
     it "should pass missing class method calls on to the wrapped class" do
@@ -195,7 +196,7 @@ describe Draper::Base do
     end
   end
 
-  context("selecting methods") do
+  describe "method selection" do
     it "echos the methods of the wrapped class except default exclusions" do
       source.methods.each do |method|
         unless Draper::Base::DEFAULT_DENIED.include?(method)
@@ -208,27 +209,48 @@ describe Draper::Base do
       DecoratorWithApplicationHelper.new(source).length.should == "overridden"
     end
 
-    it "should always proxy to_param" do
-      source.send :class_eval, "def to_param; 1; end"
-      Draper::Base.new(source).to_param.should == 1
-    end
-
-    it "should always proxy id" do
-      source.send :class_eval, "def id; 123456789; end"
-      Draper::Base.new(source).id.should == 123456789
-    end
-
     it "should not copy the .class, .inspect, or other existing methods" do
       source.class.should_not == subject.class
       source.inspect.should_not == subject.inspect
       source.to_s.should_not == subject.to_s
     end
+
+    context "when an ActiveModel descendant" do
+      it "should always proxy to_param" do
+        source.stub(:to_param).and_return(1)
+        Draper::Base.new(source).to_param.should == 1
+      end
+
+      it "should always proxy id" do
+        source.stub(:id).and_return(123456789)
+        Draper::Base.new(source).id.should == 123456789
+      end
+
+      it "should always proxy errors" do
+        Draper::Base.new(source).errors.should be_an_instance_of ActiveModel::Errors
+      end
+    end
+
+    context "when not an ActiveModel descendant" do
+      it "does not proxy to_param" do
+        non_active_model_source.stub(:to_param).and_return(1)
+        Draper::Base.new(non_active_model_source).to_param.should_not == 1
+      end
+
+      it "does not proxy errors" do
+        Draper::Base.new(non_active_model_source).should_not respond_to :errors
+      end
+    end
   end
 
   context 'the decorated model' do
     it 'receives the mixin' do
       source.class.ancestors.include?(Draper::ModelSupport)
     end
+
+    it 'includes ActiveModel support' do
+      source.class.ancestors.include?(Draper::ActiveModelSupport)
+    end
   end
 
   it "should wrap source methods so they still accept blocks" do

spec/draper/model_support_spec.rb

@@ -1,6 +1,6 @@
 require 'spec_helper'
 
-describe Draper::ModelSupport do
+describe Draper::ActiveModelSupport do
   subject { Product.new }
 
   describe '#decorator' do

spec/spec_helper.rb

@@ -2,20 +2,22 @@ require 'rubygems'
 require 'bundler/setup'
 Bundler.require
 
-require './spec/support/samples/active_record.rb'
-require './spec/support/samples/application_controller.rb'
-require './spec/support/samples/application_helper.rb'
-require './spec/support/samples/decorator.rb'
-require './spec/support/samples/decorator_with_allows.rb'
-require './spec/support/samples/decorator_with_multiple_allows.rb'
-require './spec/support/samples/decorator_with_application_helper.rb'
-require './spec/support/samples/decorator_with_denies.rb'
-require './spec/support/samples/namespaced_product.rb'
-require './spec/support/samples/namespaced_product_decorator.rb'
-require './spec/support/samples/product.rb'
-require './spec/support/samples/product_decorator.rb'
-require './spec/support/samples/specific_product_decorator.rb'
-require './spec/support/samples/some_thing.rb'
-require './spec/support/samples/some_thing_decorator.rb'
-require './spec/support/samples/widget.rb'
-require './spec/support/samples/widget_decorator.rb'
+require './spec/support/samples/active_model'
+require './spec/support/samples/active_record'
+require './spec/support/samples/application_controller'
+require './spec/support/samples/application_helper'
+require './spec/support/samples/decorator'
+require './spec/support/samples/decorator_with_allows'
+require './spec/support/samples/decorator_with_multiple_allows'
+require './spec/support/samples/decorator_with_application_helper'
+require './spec/support/samples/decorator_with_denies'
+require './spec/support/samples/namespaced_product'
+require './spec/support/samples/namespaced_product_decorator'
+require './spec/support/samples/non_active_model_product'
+require './spec/support/samples/product'
+require './spec/support/samples/product_decorator'
+require './spec/support/samples/specific_product_decorator'
+require './spec/support/samples/some_thing'
+require './spec/support/samples/some_thing_decorator'
+require './spec/support/samples/widget'
+require './spec/support/samples/widget_decorator'

spec/support/samples/active_model.rb

@@ -0,0 +1,9 @@
+module ActiveModel
+  module Conversion; end
+  module Validations; end
+
+  class Errors
+    def initialize(params = nil)
+    end
+  end
+end

spec/support/samples/active_record.rb

@@ -1,5 +1,13 @@
 module ActiveRecord
   class Base
+    include ActiveModel::Validations
+    include ActiveModel::Conversion
+
+    attr_reader :errors, :to_model
+
+    def initialize
+      @errors = ActiveModel::Errors.new(self)
+    end
 
     def self.limit
       self

spec/support/samples/non_active_model_product.rb

@@ -0,0 +1,2 @@
+class NonActiveModelProduct
+end