--- a/mercurial/dirstateguard.py	Mon Aug 14 16:26:36 2017 -0700
+++ b/mercurial/dirstateguard.py	Fri Jul 28 22:42:10 2017 -0700
@@ -11,9 +11,10 @@
 
 from . import (
     error,
+    util,
 )
 
-class dirstateguard(object):
+class dirstateguard(util.transactional):
     '''Restore dirstate at unexpected failure.
 
     At the construction, this class does:
@@ -43,16 +44,6 @@
             # ``release(tr, ....)``.
             self._abort()
 
-    def __enter__(self):
-        return self
-
-    def __exit__(self, exc_type, exc_val, exc_tb):
-        try:
-            if exc_type is None:
-                self.close()
-        finally:
-            self.release()
-
     def close(self):
         if not self._active: # already inactivated
             msg = (_("can't close already inactivated backup: %s")