diff -r fd78276948b4 -r 0217f75b6e59 mercurial/dirstate.py
--- a/mercurial/dirstate.py	Fri Oct 27 18:19:07 2017 +0200
+++ b/mercurial/dirstate.py	Thu Oct 26 16:15:31 2017 -0700
@@ -593,8 +593,7 @@
         return path
 
     def clear(self):
-        self._map = dirstatemap(self._ui, self._opener, self._root)
-        self._map.setparents(nullid, nullid)
+        self._map.clear()
         self._lastnormaltime = 0
         self._updatedfiles.clear()
         self._dirty = True
@@ -1210,6 +1209,11 @@
         # for consistent view between _pl() and _read() invocations
         self._pendingmode = None
 
+    def clear(self):
+        self._map = {}
+        self.copymap = {}
+        self.setparents(nullid, nullid)
+
     def iteritems(self):
         return self._map.iteritems()