title: Sprockets directives and slim templates
body: <p>I'm trying get work Sprockets directives in Slim templates inside rails assets pipeline.</p>
  
  <p>This is how I embed slim into pipeline:</p>
  
  <pre><code>config.assets.configure do |env|
    env.register_mime_type 'text/slim', extensions: ['.slim']
    env.register_engine '.slim', Slim::Template, mime_type: 'text/slim'
    env.register_preprocessor 'text/html', Sprockets::DirectiveProcessor.new(comments: ["//"])
    env.register_preprocessor 'text/slim', Sprockets::DirectiveProcessor.new(comments: ["//"])
  end
  </code></pre>
  
  <p>But directives like depend_on or require don't recognized by pipeline inside slim templates in development environment.</p>
  
  <p>I have Rails 4.2.4. and Sprockets 3.4.0</p>
  
  <p>Where I'm wrong?</p>