--- a/hgext/states.py	Sun Sep 25 12:43:00 2011 +0200
+++ b/hgext/states.py	Thu Sep 22 19:18:40 2011 +0200
@@ -517,7 +517,7 @@
                 return 1
             if off:
                 if st in repo._enabledstates:
-                    repo._enabledstates.remove(st)
+                    repo.disablestate(st)
                 else:
                     ui.write_err(_('state %s already deactivated\n') %
                                  state_name)
@@ -786,7 +786,24 @@
                         break
             return state
 
-
+        def disablestate(self, state):
+            """Disable empty state.
+            Raise error.Abort if the state is not empty.
+            """
+            # the lowest is mandatory
+            if state == ST0:
+                raise error.Abort(_('could not disable %s' % state.name))
+            enabled =  self._enabledstates
+            # look up for lower state that is enabled (at least published)
+            lower = max(st for st in self._enabledstates if st < state)
+            if repo.stateheads(state) != repo.stateheads(lower):
+                raise error.Abort(
+                    _('could not disable non empty state %s' % state.name),
+                    hint=_("You may want to use `hg %s '%sheads()'`"
+                            % (lower.name, state.name))
+                    )
+            else:
+                enabled.remove(state)
 
         def stateheads(self, state):
             """Return the set of head that define the state"""