We have MultiCollector to enable running multiple Collectors on the same hits, in sequence for each hit. I think a nice extension would be to enable filtering so that earlier collectors could reject a hit, preventing later collectors from seeing it. This way you could have a post-filter implemented in one collector, and some other collection, like faceting, in the next one, that wants to ignore hits that are filtered in this post-filter.
The implementation idea would be to return a "status" value from LeafCollector.collect() indicating how to proceed. This could also naturally be used for early termination (you could have status=TERMINATE | SKIP | COLLECT, say). I was trying to undertsand why this wasn't done before for early termination since it seemed so natural to me, and thought - there must be a reason. But I went and read through (skimmed really) the original EarlyTerminatingCollector issue ( https://issues.apache.org/jira/browse/LUCENE-4858) and didn't see any discussion of that. Am I missing something here? -Mike
