diff -r 70ca0e846d25 -r 8f40e21ca842 mercurial/exthelper.py
--- a/mercurial/exthelper.py	Thu Dec 27 21:55:22 2018 -0500
+++ b/mercurial/exthelper.py	Thu Dec 27 23:46:35 2018 -0500
@@ -40,6 +40,7 @@
         self.command = registrar.command(self.cmdtable)
         self.configtable = {}
         self.configitem = registrar.configitem(self.configtable)
+        self.filesetpredicate = registrar.filesetpredicate()
         self.revsetpredicate = registrar.revsetpredicate()
         self.templatekeyword = registrar.templatekeyword()
 
@@ -48,6 +49,7 @@
         self._uipopulatecallables.extend(other._uipopulatecallables)
         self._extcallables.extend(other._extcallables)
         self._repocallables.extend(other._repocallables)
+        self.filesetpredicate._table.update(other.filesetpredicate._table)
         self.revsetpredicate._table.update(other.revsetpredicate._table)
         self.templatekeyword._table.update(other.templatekeyword._table)
         self._commandwrappers.extend(other._commandwrappers)