Rails default form errors

snippet.rb

ActionView::Base.field_error_proc = Proc.new do |html_tag, instance_tag|
  fragment = Nokogiri::HTML.fragment(html_tag)
  field = fragment.at('input,select,textarea')

  error_message = instance_tag.error_message.join(", ")

  html = if field
           debugger
           field.add_class("is-danger")
           html = <<-HTML
              #{fragment.to_s}
              <p class="help is-danger">#{error_message}</p>
           HTML
           html
         else
           html_tag
         end

  html.html_safe
end

# Source:
https://github.com/rails/rails/blob/7c68c5210cbc245d778daa7958cab73bc74f4669/actionview/lib/action_view/base.rb#L162