gistfile1.rb

# http://m.onkey.org/2009/7/7/nested-layouts

# The "no block given" error crops up in lib/action_view/render/rendering.rb in actionpack.
# The #_render_template method # is failing to pass a block to template.render on line 101.  

# The problem appears to already be fixed in edge, but until then you could try this:

#config/initializers/duck_punch_rendering.rb
require 'active_support/core_ext/object/try'

module ActionView
  module Rendering
    
    def _render_template(template, layout = nil, options = {})
      locals = options[:locals] || {}

      ActiveSupport::Notifications.instrument("action_view.render_template",
        :identifier => template.identifier, :layout => layout.try(:identifier)) do

        content = template.render(self, locals) { |*name| _layout_for(*name) }
        @_content_for[:layout] = content

        if layout
          @_layout = layout.identifier
          content  = _render_layout(layout, locals)
        end

        content
      end
    end
    
  end
end
# eof

# Notice the { |*name| _layout_for(*name) } block, which is the thing living on the other
# side of your template's yields.

# parent_layout becomes
module ApplicationHelper
  def parent_layout(layout)
    @_content_for[:layout] = self.output_buffer
    self.output_buffer = render :file => "layouts/#{layout}"
  end
end
# eof