    # File lib/compass/commands/update_project.rb, line 53
          def new_compiler_instance(additional_options = {})
            @compiler_opts ||= begin
              compiler_opts = {:sass => Compass.sass_engine_options}
              compiler_opts.merge!(options)
              compiler_opts[:sass_files] = explicit_sass_files
              compiler_opts[:cache_location] = determine_cache_location
              compiler_opts
            end

            @memory_store ||= Sass::CacheStores::Memory.new
            @backing_store ||= compiler_opts[:cache_store]
            @backing_store ||= Sass::CacheStores::Filesystem.new(determine_cache_location)
            @cache_store ||= Sass::CacheStores::Chain.new(@memory_store, @backing_store)
            @memory_store.reset!

            Compass::Compiler.new(
              working_path,
              Compass.configuration.sass_path,
              Compass.configuration.css_path,
              @compiler_opts.merge(:cache_store => @cache_store).merge(additional_options)
            )
          end