[PATCH 3 of 3] dirstate: add exception when calling setparent without begin/end

[Durham Goode]

# HG changeset patch
# User Durham Goode <durham at fb.com>
# Date 1409942264 25200
#      Fri Sep 05 11:37:44 2014 -0700
# Node ID cbc8f6a95fd203e455c5acd0cf6f6006663af52f
# Parent  ca5a5cd5a9840dd3d391a6204f5e3edb8b097b44
dirstate: add exception when calling setparent without begin/end

Adds an exception when calling dirstate.setparent without having first called
dirstate.beginparentchange. This will prevent people from writing code that
modifies the dirstate parent without considering the transactionality of their
change.

This will break third party extensions that call setparents.

diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
--- a/mercurial/dirstate.py
+++ b/mercurial/dirstate.py
@@ -243,6 +243,10 @@
 
         See localrepo.setparents()
         """
+        if self._parentwriters == 0:
+            raise util.Abort(_("cannot set dirstate parent without " +
+                " calling dirstate.begingparentchange"))
+
         self._dirty = self._dirtypl = True
         oldp2 = self._pl[1]
         self._pl = p1, p2