# Create and fill the header of a unit file `file`.
	#
	# A unit file is a Nit source file generated from one
	# or more docunits that will be compiled and executed.
	#
	# The handled on the file is returned and must be completed and closed.
	#
	# `file` should be a valid filepath for a Nit source file.
	private fun create_unitfile(file: String): Writer
	do
		var mmodule = self.mmodule
		var dir = file.dirname
		if dir != "" then dir.mkdir
		var f
		f = new FileWriter.open(file)
		f.write("# GENERATED FILE\n")
		f.write("# Docunits extracted from comments\n")
		if mmodule != null then
			f.write("intrude import {mmodule.name}\n")
		end
		f.write("\n")
		return f
	end