diff -r 1b9b00aca8a3 -r 413b44003462 mercurial/ancestor.py
--- a/mercurial/ancestor.py	Mon Mar 13 21:58:43 2017 -0700
+++ b/mercurial/ancestor.py	Mon Mar 13 12:40:14 2017 -0700
@@ -296,6 +296,8 @@
         except StopIteration:
             return False
 
+    __bool__ = __nonzero__
+
     def __iter__(self):
         """Generate the ancestors of _initrevs in reverse topological order.