[PATCH 4 of 6] revset: fix a crash with 'p2(wdir())'

[Matt Harbison]

# HG changeset patch
# User Matt Harbison <matt_harbison at yahoo.com>
# Date 1435713945 14400
#      Tue Jun 30 21:25:45 2015 -0400
# Node ID 4a504f9bae9718664cc685397ff066e93c163327
# Parent  6e20445b1da8baefbb48bae7af20dfcb2699c9ce
revset: fix a crash with 'p2(wdir())'

The crash was "TypeError: expected string or Unicode object, NoneType found"
down in revlog.parentrevs().

diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1476,7 +1476,13 @@
     ps = set()
     cl = repo.changelog
     for r in getset(repo, fullreposet(repo), x):
-        ps.add(cl.parentrevs(r)[1])
+        if r is None:
+            parents = repo[r].parents()
+            if len(parents) > 1:
+                ps.update([parents[1].rev()])
+        else:
+            ps.add(cl.parentrevs(r)[1])
+
     ps -= set([node.nullrev])
     # XXX we should turn this into a baseset instead of a set, smartset may do
     # some optimisations from the fact this is a baseset.
diff --git a/tests/test-merge-default.t b/tests/test-merge-default.t
--- a/tests/test-merge-default.t
+++ b/tests/test-merge-default.t
@@ -74,6 +74,12 @@
   date:        Thu Jan 01 00:00:00 1970 +0000
   summary:     e
   
+  $ hg log -r 'p2(wdir())'
+  changeset:   2:2d95304fed5d
+  user:        test
+  date:        Thu Jan 01 00:00:00 1970 +0000
+  summary:     c
+  
   $ hg commit -mm1
 
 Should succeed - 2 heads: