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diff --git a/Tools/flex.py b/Tools/flex.py
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+#!/usr/bin/env python
+# encoding: utf-8
+# John O'Meara, 2006
+# Thomas Nagy, 2006-2018 (ita)
+
+"""
+The **flex** program is a code generator which creates C or C++ files.
+The generated files are compiled into object files.
+"""
+
+import os, re
+from waflib import Task, TaskGen
+from waflib.Tools import ccroot
+
+def decide_ext(self, node):
+	if 'cxx' in self.features:
+		return ['.lex.cc']
+	return ['.lex.c']
+
+def flexfun(tsk):
+	env = tsk.env
+	bld = tsk.generator.bld
+	wd = bld.variant_dir
+	def to_list(xx):
+		if isinstance(xx, str):
+			return [xx]
+		return xx
+	tsk.last_cmd = lst = []
+	lst.extend(to_list(env.FLEX))
+	lst.extend(to_list(env.FLEXFLAGS))
+	inputs = [a.path_from(tsk.get_cwd()) for a in tsk.inputs]
+	if env.FLEX_MSYS:
+		inputs = [x.replace(os.sep, '/') for x in inputs]
+	lst.extend(inputs)
+	lst = [x for x in lst if x]
+	txt = bld.cmd_and_log(lst, cwd=wd, env=env.env or None, quiet=0)
+	tsk.outputs[0].write(txt.replace('\r\n', '\n').replace('\r', '\n')) # issue #1207
+
+TaskGen.declare_chain(
+	name = 'flex',
+	rule = flexfun, # issue #854
+	ext_in = '.l',
+	decider = decide_ext,
+)
+
+# To support the following:
+# bld(features='c', flexflags='-P/foo')
+Task.classes['flex'].vars = ['FLEXFLAGS', 'FLEX']
+ccroot.USELIB_VARS['c'].add('FLEXFLAGS')
+ccroot.USELIB_VARS['cxx'].add('FLEXFLAGS')
+
+def configure(conf):
+	"""
+	Detect the *flex* program
+	"""
+	conf.find_program('flex', var='FLEX')
+	conf.env.FLEXFLAGS = ['-t']
+
+	if re.search (r"\\msys\\[0-9.]+\\bin\\flex.exe$", conf.env.FLEX[0]):
+		# this is the flex shipped with MSYS
+		conf.env.FLEX_MSYS = True
+