@@ -53,4 +53,8 @@ public abstract class FilterLeafCollector implements LeafCollector {
     return name + "(" + in + ")";
   }
 
+  @Override
+  public DocIdSetIterator competitiveIterator() {
+    return in.competitiveIterator();
+  }
 }
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 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
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 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.lucene.search;


import java.io.IOException;

/**
 * {@link LeafCollector} delegator.
 *
 * @lucene.experimental
 */
public abstract class FilterLeafCollector implements LeafCollector {

  protected final LeafCollector in;

  /** Sole constructor. */
  public FilterLeafCollector(LeafCollector in) {
    this.in = in;
  }

  @Override
  public void setScorer(Scorable scorer) throws IOException {
    in.setScorer(scorer);
  }

  @Override
  public void collect(int doc) throws IOException {
    in.collect(doc);
  }

  @Override
  public String toString() {
    String name = getClass().getSimpleName();
    if (name.length() == 0) {
      // an anonoymous subclass will have empty name?
      name = "FilterLeafCollector";
    }
    return name + "(" + in + ")";
  }

}

We've had endless discussions about whether or not to delegate in FilterXXX classes and I think that the consensus is that we should only delegate abstract methods. Since this one has a default implementation, let's not delegate and look for extensions of FilterCollector that should delegate it? (e.g. asserting collectors)