haml_tag outputs directly to the Haml template

Question

What am I doing wrong with this helper for my HAML template?

  def display_event(event)
    event = MultiJson.decode(event)
    markup_class = get_markup_class(event)
    haml_tag :li, :class => markup_class do
      haml_tag :b, "Foo"
      haml_tag :i, "Bar"
    end
  end

This is the error:

haml_tag outputs directly to the Haml template.
Disregard its return value and use the - operator,
or use capture_haml to get the value as a String.

The template is calling display_event like this:

 - @events.each do |event|
     = display_event(event)

If I was using regular markup it would expand to the following

%li.fooclass
   %b Foo
   %i Bar

Answer 1

The clue’s in the error message:

Disregard its return value and use the - operator,
or use capture_haml to get the value as a String.

From the docs for haml_tag:

haml_tag outputs directly to the buffer; its return value should not be used. If you need to get the results as a string, use #capture_haml.

To fix it, either change your Haml to:

- @events.each do |event|
  - display_event(event)

(i.e. use the - operator instead of =), or change the method to use capture_haml:

def display_event()
  event = MultiJson.decode(event)
  markup_class = get_markup_class(event)
  capture_haml do
    haml_tag :li, :class => markup_class do
      haml_tag :b, "Foo"
      haml_tag :i, "Bar"
    end
  end
end

This will make the method return a string, which you can then display with = in your Haml.

Note you need to make only one of these changes, if you make both they will cancel each other out and you’ll get nothing displayed.