code: def remoteIndexer1to2(oldIndexer):
      
      newIndexer = oldIndexer.upgradeVersion(
          oldIndexer.typeName, 1, 2,
          indexCount=oldIndexer.indexCount,
          installedOn=oldIndexer.installedOn,
          indexDirectory=oldIndexer.indexDirectory)
  
      listeners = newIndexer.store.query(
          batch._ReliableListener,
          batch._ReliableListener.listener == newIndexer)
  
      for listener in listeners:
          _IndexerInputSource(
              store=newIndexer.store,
              indexer=newIndexer,
              source=listener.processor)
  
      return newIndexer
docs: Previously external application code was responsible for adding a
      RemoteListener to a batch work source as a reliable listener.  This
      precluded the possibility of the RemoteListener resetting itself
      unilaterally.  With version 2, RemoteListener takes control of adding
      itself as a reliable listener and keeps track of the sources with which it
      is associated.  This upgrader creates that tracking state.