A monkey patch to include an html comment where a template starts and stops in development mode for rails

haml_filename_comment.rb

Haml::Engine.class_eval do
    alias_method :initialize_without_file_comments, :initialize

    def initialize(template, options ={})
        template = template.dup
        template.insert(0,"/ BEGIN #{options[:filename]}\n")
        template.insert(-1,"\n/ END #{options[:filename]}")
        template.freeze
        initialize_without_file_comments(template, options)
    end

end if Rails.env.development?