--- a/hgext/convert/common.py	Fri Feb 10 22:25:49 2012 +0100
+++ b/hgext/convert/common.py	Fri Feb 10 22:34:13 2012 +0100
@@ -245,6 +245,10 @@
         """
         pass
 
+    def hascommit(self, rev):
+        """Return True if the sink contains rev"""
+        raise NotImplementedError()
+
 class commandline(object):
     def __init__(self, ui, command):
         self.ui = ui