From 3a688dc4b7e0a023a7654cc47c390cc88606d57f Mon Sep 17 00:00:00 2001
From: Dylan Baker <dylan@pnwbakers.com>
Date: Mon, 8 May 2017 10:37:34 -0700
Subject: [PATCH] Implement difference method for OrderedSet

This implementation is obvious rather than efficient, but it's efficient
enough for our uses I think. It uses `type(self)` to guarantee that it
works even in subclasses or if the name of the class changes.
---
 mesonbuild/mesonlib.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mesonbuild/mesonlib.py b/mesonbuild/mesonlib.py
index d97ebbe99..7248be9c1 100644
--- a/mesonbuild/mesonlib.py
+++ b/mesonbuild/mesonlib.py
@@ -722,3 +722,6 @@ class OrderedSet(collections.MutableSet):
     def update(self, iterable):
         for item in iterable:
             self.__container[item] = None
+
+    def difference(self, set_):
+        return type(self)(e for e in self if e not in set_)