[PATCH 4 of 7] context: migrate to context manager for changing dirstate parents

[Augie Fackler]

# HG changeset patch
# User Augie Fackler <augie at google.com>
# Date 1495141867 14400
#      Thu May 18 17:11:07 2017 -0400
# Node ID 6b988519e85f29c9c273f30c742ca0877aa824a1
# Parent  045240d198722437267f7d2dadb1c1dbfae971ee
context: migrate to context manager for changing dirstate parents

diff --git a/mercurial/context.py b/mercurial/context.py
--- a/mercurial/context.py
+++ b/mercurial/context.py
@@ -1447,13 +1447,12 @@ class committablectx(basectx):
 
         """
 
-        self._repo.dirstate.beginparentchange()
-        for f in self.modified() + self.added():
-            self._repo.dirstate.normal(f)
-        for f in self.removed():
-            self._repo.dirstate.drop(f)
-        self._repo.dirstate.setparents(node)
-        self._repo.dirstate.endparentchange()
+        with self._repo.dirstate.parentchange():
+            for f in self.modified() + self.added():
+                self._repo.dirstate.normal(f)
+            for f in self.removed():
+                self._repo.dirstate.drop(f)
+            self._repo.dirstate.setparents(node)
 
         # write changes out explicitly, because nesting wlock at
         # runtime may prevent 'wlock.release()' in 'repo.commit()'