title: form_for nested resource (singular) not using correct path helper
body: <p>I'm probably doing something stupid, but...</p>
  
  <p>app/model/user.rb:</p>
  
  <pre><code>class User &lt; ActiveRecord::Base
  has_one :totem
  </code></pre>
  
  <p>config/routes.rb:</p>
  
  <pre><code>resources :users do
      resource :totem
  end
  </code></pre>
  
  <p>app/controllers/totems_controller.rb:</p>
  
  <pre><code>class TotemsController &lt; ApplicationController
  
      before_filter do
          @user = User.find(params[:user_id])
      end
  
      def new
          @totem = @user.build_totem
      end
  
  end
  </code></pre>
  
  <p>app/views/totems/new.html.erb:</p>
  
  <pre><code>&lt;%= form_for [@user, @totem] do |f| %&gt;
  &lt;% end %&gt;
  </code></pre>
  
  <p>Then, when I navigate to <code>/users/123/totem/new</code>, I get  the error:</p>
  
  <pre><code>ActionView::Template::Error (undefined method `user_totems_path' for #&lt;#&lt;Class:0x007f9d3c843b00&gt;:0x007f9d3bb6dd68&gt;):
  </code></pre>
  
  <p>But because I'm using <code>resource :totem</code> instead of <code>resources :totems</code> in routes.rb, the path helper it should be using is <code>user_totem_path</code>. Why isn't it trying to use the correct path helper?</p>