module Tilt

def self.finalize!

This also freezes Tilt itself.
is called, all attempts to modify the default mapping will fail.
libraries you desire to use have already been loaded. Once this is
mapping. This can be done to improve performance after the template
Replace the default mapping with a finalized version of the default 
def self.finalize!
  return self if @default_mapping.is_a?(FinalizedMapping)
  class << self
    prepend(Module.new do
      def lazy_map(*)
        raise "Tilt.#{__callee__} not supported after Tilt.finalize! has been called"
      end
      alias register lazy_map
      alias register_lazy lazy_map
      alias register_pipeline lazy_map
      alias prefer lazy_map
    end)
  end
  @default_mapping = @default_mapping.finalized
  freeze
end