private fun compute_header_dependencies(v: HeaderDependancyPhase)
	do
		if header_dependencies != null then return

		var header_dependencies = new HashSet[MModule]

		# gather from importation
		for m in in_importation.direct_greaters do
			m.compute_header_dependencies v

			# does the super module has inherited dependencies?
			var hd = m.header_dependencies
			assert hd != null
			if not hd.is_empty then
				header_dependencies.add_all hd
			end

			# does the super module itself has extern dependencies?
			var amodule = v.toolcontext.modelbuilder.mmodule2node(m)
			if amodule != null and amodule.has_public_c_header then header_dependencies.add(m)
		end

		self.header_dependencies = header_dependencies
	end