shitlist.rb

module Shitlist
  def shitlist(method_name, whitelist)
    original_method = instance_method(method_name)
    undef_method(method_name)

    define_method(method_name) do |*args, &block|
      call = caller_locations.first
      passes_whitelist = whitelist.any? do |label, file_pattern|
        call.label == label && call.absolute_path.end_with?(file_pattern)
      end

      unless passes_whitelist
        fail "Shitlisted method! Permitted callers: #{whitelist}"
      end

      original_method.bind(self).call(*args, &block)
    end
  end
end

class Example
  extend Shitlist

  def not_on_shitlist
    qux
  end

  def baz
    qux
  end

  def qux
    puts 'Only some methods can call me :)'
  end
  shitlist :qux, 'baz' => 'shitlist.rb'
end

example = Example.new

# This will work
example.baz

# This will fail
example.not_on_shitlist