# Force the identification of all MModule of the group and sub-groups in the file system.
	#
	# When a group is scanned, its sub-groups hierarchy is filled (see `MGroup::in_nesting`)
	# and the potential modules (and nested modules) are identified (see `MGroup::modules`).
	#
	# Basically, this recursively call `identify_group` and `identify_module` on each directory entry.
	#
	# No-op if the group was already scanned (see `MGroup::scanned`).
	fun scan_group(mgroup: MGroup) do
		if mgroup.scanned then return
		mgroup.scanned = true
		var p = mgroup.filepath
		# a virtual group has nothing to scan
		if p == null then return
		var files = p.files
		alpha_comparator.sort(files)
		for f in files do
			if f.first == '.' then continue
			var fp = p/f
			var g = identify_group(fp)
			# Recursively scan for groups of the same package
			if g == null then
				identify_module(fp)
			else if g.mpackage == mgroup.mpackage then
				scan_group(g)
			end
		end
	end