ruby on rails: (eval):1: syntax error, unexpected $undefined

Question

I'm getting the following syntax error:

(eval):1: syntax error, unexpected $undefined
$#<MenuBuilder:0x007fccee84e7f8> = #<MENUBUILDER:0X007FCCEE84E7F8>
 ^

This is code execution:

_main_menu.html.haml

#main-menu 
  = menu do |m| 
    = m.submenu "Products" do 
      = m.item "Products", Product 

builders_helper.rb

module BuildersHelper 
  def menu(options = {}, &block) 
    MenuBuilder.new(self).root(options, &block) 
  end 
end 

menu_builder.rb

class MenuBuilder 
  attr_accessor :template 
  def initialize(template) 
    @template = template 
  end 
  def root(options, &block) 
    options[:class] = "jd_menu jd_menu_slate ui-corner-all" 
    content_tag :ul, capture(self, &block), options 
  end 
  def item(title, url, options = {}) 
    content_tag :li, options do 
      url = ajax_route(url) unless String === url 
      url = dash_path + url if url.starts_with?("#") 
      link_to title, url 
    end 
  end 
  def submenu(title, options = {}, &block) 
    content_tag :li do 
      content_tag(:h6, title.t) + 
      content_tag(:ul, capture(self, &block), :class => "ui-corner- 
all") 
    end 
  end 
end 

It fails on the capture() call in the root method:

content_tag :ul, capture(self, &block), options

self refers to the instance of MenuBuilder and I am positive that a block is passed as the other parameter. If I throw a puts statement in an if block_given? it will execute, but it wont get passed that content_tag line above.

Answer 1

The issue looks like it's in your use of the capture helper method .

That method accepts a block of view code and assigns it to a variable that can be used elsewhere in your view.

Here's more info: http://api.rubyonrails.org/classes/ActionView/Helpers/CaptureHelper.html#method-i-capture

Are you sure you're actually passing a block into the code the executes the capture?

You might consider something like this:

content_tag :li do 
  if block_given?
    content_tag(:h6, title.t) + 
    content_tag(:ul, capture(self, &block), :class => "ui-corner-all") 
  else
    content_tag(:h6, title.t) # whatever is appropriate if there's no block passed
  end
end 

Answer 2

Okay, I just had this problem, and I think I figured out how to fix it. The problem is most likely a bug introduced into ActiveRecord where they're overriding Kernel.capture. The fix, I've found, is to use the helper module's capture instead of the class-level capture. So in your case, where you're calling content_tag :ul, capture(self, &block), options , try calling content_tag :ul, @template.capture(self, &block), options instead so you use the helper module's capture method instead of the shoddy one from AR.

Check out these github issues for some more info.