FilteredQuery within BooleanQuery issue

[Erik Hatcher]

I've run into what I feel is an issue with FilteredQuery.  The best  
description is an example.  First I've indexed three documents:

  public void setUp() throws IOException {
    RAMDirectory directory = new RAMDirectory();
    IndexWriter writer = new IndexWriter(directory, new  
WhitespaceAnalyzer(), true);
    Document doc = new Document();
    doc.add(new Field("field", "zero", Field.Store.YES,  
Field.Index.TOKENIZED));
    writer.addDocument(doc);
    doc = new Document();
    doc.add(new Field("field", "one", Field.Store.YES,  
Field.Index.TOKENIZED));
    writer.addDocument(doc);
    writer.close();

    doc = new Document();
    doc.add(new Field("field", "two", Field.Store.YES,  
Field.Index.TOKENIZED));
    writer.addDocument(doc);
    writer.close();

    searcher = new IndexSearcher(directory);
  }

Now for a mock filter to keep things simple:

public class DummyFilter extends Filter {
  private int doc;

  public DummyFilter(int doc) {
    this.doc = doc;
  }


  public BitSet bits(IndexReader reader) throws IOException {
    BitSet bits = new BitSet(reader.maxDoc());
    bits.set(doc);
    return bits;
  }
}

And finally a test case that fails:

  public void testBoolean() throws Exception {
    BooleanQuery bq = new BooleanQuery();
    Query query = new FilteredQuery(new MatchAllDocsQuery(),
        new DummyFilter(0));
    bq.add(query, BooleanClause.Occur.MUST);
    query = new FilteredQuery(new MatchAllDocsQuery(),
        new DummyFilter(1));
    bq.add(query, BooleanClause.Occur.MUST);
    Hits hits = searcher.search(bq);
    assertEquals(0, hits.length());  // fails: hits.length() == 2
  }

I expect no documents should match this BooleanQuery, but yet two  
documents match (id's 0 and 1).  Am I right in thinking that no  
documents should match since each required clause selects a different  
document so there is no intersection?  If so, what's the flaw in  
FilteredQuery that causes this?   If I'm wrong in my assertion, how so?

For comparison, a ChainedFilter does do what I expect:

  public void testChainedFilter() throws Exception {
    ChainedFilter filter = new ChainedFilter(
        new Filter[] {new DummyFilter(0), new DummyFilter(1)},
        ChainedFilter.AND);
    Hits hits = searcher.search(new MatchAllDocsQuery(), filter);
    assertEquals(0, hits.length());  // passes
  }

Thanks,
        Erik


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