Monkeypatch ActionController::Base.

We need to be able to let draper get a copy of the view_context
no matter what happens. AC::Base doesn't really let us do that. So
we have to monkeypatch.

This was originally suggested in
https://github.com/jcasimir/draper/issues/124#issuecomment-6954291
by @rf-.

It appears to be the cleanest way to take care of this problem, and
shouldn't affect any other things, since we keep the exact same
semantics of view_context.

Theoretically:

Fixes #124
Fixes #109

lib/draper.rb

@@ -10,6 +10,7 @@ require 'draper/helper_support'
 require 'draper/view_context'
 require 'draper/decorated_enumerable_proxy'
 require 'draper/railtie' if defined?(Rails)
+require 'draper/action_controller/base'
 
 # Test Support
 require 'draper/test/rspec_integration'    if defined?(RSpec) and RSpec.respond_to?(:configure)

lib/draper/action_controller/base.rb

@@ -0,0 +1,9 @@
+module DraperViewContext
+  def view_context
+    super.tap do |context|
+      Draper::ViewContext.current = context
+    end
+  end
+end
+
+ApplicationController.send(:include, DraperViewContext)

lib/draper/system.rb

@@ -2,7 +2,6 @@ module Draper
   class System
     def self.setup(component)
       component.class_eval do
-        include Draper::ViewContextFilter
         extend  Draper::HelperSupport unless defined?(::ActionMailer) && self.is_a?(::ActionMailer::Base)
       end
     end

lib/draper/test/view_context.rb

@@ -2,7 +2,7 @@ module Draper
   module ViewContext
     def self.infect!(context)
       context.instance_eval do
-        ApplicationController.new.set_current_view_context
+        ApplicationController.new.view_context
         Draper::ViewContext.current.controller.request ||= ActionController::TestRequest.new
         Draper::ViewContext.current.request            ||= Draper::ViewContext.current.controller.request
         Draper::ViewContext.current.params             ||= {}

lib/draper/view_context.rb

@@ -8,14 +8,4 @@ module Draper
       Thread.current[:current_view_context] = input
     end
   end
-
-  module ViewContextFilter
-    def set_current_view_context
-      Draper::ViewContext.current = self.view_context
-    end
-
-    def self.included(source)
-      source.send(:before_filter, :set_current_view_context) if source.respond_to?(:before_filter)
-    end
-  end
 end

spec/draper/base_spec.rb

@@ -1,7 +1,7 @@
 require 'spec_helper'
 
 describe Draper::Base do
-  before(:each){ ApplicationController.new.set_current_view_context }
+  before(:each){ ApplicationController.new.view_context }
   subject{ Decorator.new(source) }
   let(:source){ Product.new }
   let(:non_active_model_source){ NonActiveModelProduct.new }

spec/draper/view_context_spec.rb

@@ -5,19 +5,6 @@ describe Draper::ViewContext do
   let(:app_controller) { ApplicationController }
   let(:app_controller_instance) { app_controller.new }
 
-  it "implements #set_current_view_context" do
-    app_controller_instance.should respond_to(:set_current_view_context)
-  end
-
-  it "calls #before_filter with #set_current_view_context" do
-    app_controller.before_filters.should include(:set_current_view_context)
-  end
-
-  it "raises an exception if the view_context is fetched without being set" do
-    Draper::ViewContext.current = nil
-    expect {app_controller.current_view_context}.should raise_exception(Exception)
-  end
-
   it "provides a method to create a view context while testing" do
     Draper::ViewContext.should respond_to(:infect!)
   end

spec/spec_helper.rb

@@ -2,11 +2,13 @@ require 'bundler/setup'
 require 'ammeter/init'
 require 'rails'
 
+require 'action_view'
+require './spec/support/samples/application_controller'
+
 Bundler.require
 
 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'
@@ -24,3 +26,9 @@ require './spec/support/samples/some_thing'
 require './spec/support/samples/some_thing_decorator'
 require './spec/support/samples/widget'
 require './spec/support/samples/widget_decorator'
+
+module ActionController
+  class Base
+    Draper::System.setup(self)
+  end
+end

spec/support/samples/application_controller.rb

@@ -10,7 +10,14 @@ module ActionController
       @@before_filters << name
     end
 
-    Draper::System.setup(self)
+    def view_context
+#      puts "zomg view context"
+      @view_context ||= ApplicationController
+    end
+
+    def view_context=(input)
+      @view_context = input
+    end
   end
 end
 
@@ -20,14 +27,6 @@ class ApplicationController < ActionController::Base
   extend ActionView::Helpers::UrlHelper
   extend ApplicationHelper
 
-  def view_context
-    @view_context ||= ApplicationController
-  end
-
-  def view_context=(input)
-    @view_context = input
-  end
-
   def self.hello
     "Hello!"
   end