mercurial/revlog.py

--- a/mercurial/revlog.py	Mon Apr 15 01:59:11 2013 +0200
+++ b/mercurial/revlog.py	Tue Apr 16 10:08:18 2013 -0700
@@ -711,10 +711,7 @@
         if self.descendant(start, end):
             return self.node(start)
 
-        def parents(rev):
-            return [p for p in self.parentrevs(rev) if p != nullrev]
-
-        c = ancestor.ancestor(a, b, parents)
+        c = ancestor.ancestor(a, b, self.parentrevs)
         if c is None:
             return nullid