[PATCH v2] revset: prevent infinite recursion on pypy

[Maciej Fijalkowski]

# HG changeset patch
# User Maciej Fijalkowski <fijall at gmail.com>
# Date 1459498174 -7200
#      Fri Apr 01 10:09:34 2016 +0200
# Node ID 801aaa7190fc0f1ff7cf00d372581e3c00a8ad38
# Parent  25025eea0f6bf62d008d128868b53c7829c73297
revset: prevent infinite recursion on pypy

as explained in the commit, __len__ cannot do [x for x in self] because
that can potentially call __len__ again, causing infinite recursion

diff -r 25025eea0f6b -r 801aaa7190fc mercurial/revset.py
--- a/mercurial/revset.py	Thu Mar 31 15:37:21 2016 +0800
+++ b/mercurial/revset.py	Fri Apr 01 10:09:34 2016 +0200
@@ -2960,7 +2960,10 @@
 
     def __len__(self):
         # Basic implementation to be changed in future patches.
-        l = baseset([r for r in self])
+        # until this gets improved, we use generator expression
+        # here, since list compr is free to call __len__ again
+        # causing infinite recursion
+        l = baseset(r for r in self)
         return len(l)
 
     def sort(self, reverse=False):