# File lib/backports/tools/make_block_optional.rb, line 6
  def self.make_block_optional(mod, *methods)
    mod = class << mod; self; end unless mod.is_a? Module
    options = methods.last.is_a?(Hash) ? methods.pop : {}
    methods.each do |selector|
      unless mod.method_defined? selector
        warn "#{mod}##{selector} is not defined, so block can't be made optional"
        next
      end
      unless options[:force]
        # Check if needed
        test_on = options.fetch(:test_on)
        result =  begin
                    test_on.send(selector, *options.fetch(:arg, []))
                  rescue LocalJumpError
                    false
                  end
        next if result.class.name =~ /Enumerator$/
      end
      require 'enumerator'
      arity = mod.instance_method(selector).arity
      last_arg = []
      if arity < 0
        last_arg = ["*rest"]
        arity = -1-arity
      end
      arg_sequence = ((0...arity).map{|i| "arg_#{i}"} + last_arg + ["&block"]).join(", ")

      alias_method_chain(mod, selector, :optional_block) do |aliased_target, punctuation|
        mod.module_eval "def \#{aliased_target}_with_optional_block\#{punctuation}(\#{arg_sequence})\nreturn to_enum(:\#{aliased_target}_without_optional_block\#{punctuation}, \#{arg_sequence}) unless block_given?\n\#{aliased_target}_without_optional_block\#{punctuation}(\#{arg_sequence})\nend\n", __FILE__, __LINE__ + 1
      end
    end
  end