Recently I found myself wanting an IndexReader to which I could say, "pretend like documents x, y and z are deleted, but don't really delete them." To do this, I extended FilterIndexReader and overrode TermDocs, TermPositions and various other methods to run the results of the wrapped reader past a BitVector containing doc ids to filter. The issue I ran into is that with LUCENE-1483 searching bypasses the my overridden methods and goes straight to the SegmentReaders after calling getSequentialSubReaders() (which FilterIndexReader passes right through).
I'm sure I can extend my wrapping reader to also wrap whatever is returned by getSequentialSubReaders, however all of what I'm writing is already done by IndexReader with respect to deletions. What if, instead of throwing UnsupportedOperationExceptions, a read-only IndexReader did everything it normally does with deletes up to the point of actually writing the .del file. This would allow documents to be removed from the reader for the lifetime of the reader, and seems like it might be a minimal change. -Jeremy
