Padrino cannot use output helpers in custom form builder

Question

I am trying to create a custom form builder that generates a span with an error message. I keep getting the message

NoMethodError at /class/create
undefined method `content_tag' for #<Padrino::Helpers::FormBuilder::StandardFormBuilder:0x00000005aa24b8>

Here is my extension:

module Padrino
  module Helpers
    module FormBuilder
      class CustomFormBuilder < AbstractFormBuilder

        def errors_for(field)
          if object.errors[field.to_sym]
            error = object.errors[field.to_sym].first
            content_tag(:span, error, class: 'error')
          end
        end
      end
    end
  end
end

end

I have placed this extension in the lib folder.

Answer 1

You should include helper modules you need in your builder class.

module Padrino
  module Helpers
    module FormBuilder
      class CustomFormBuilder < AbstractFormBuilder
        include TagHelpers
        include FormHelpers
        include AssetTagHelpers
        include OutputHelpers

        ...your methods here...
      end
    end
  end
end