it's not possible to access sub-query's freq information if BooleanScorer is use
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                 Key: LUCENE-2684
                 URL: https://issues.apache.org/jira/browse/LUCENE-2684
             Project: Lucene - Java
          Issue Type: Bug
          Components: Search
            Reporter: Michael McCandless
             Fix For: 3.1, 4.0


LUCENE-2590 added an advanced feature, allowing an app to gather all 
sub-scorers for any Query.

This is powerful because then, during collection, the app can get some details 
about how each sub-query "participated" in the overall match for the given 
document.

However, I think this is completely broken if the BooleanQuery uses 
BooleanScorer, because that scorer is not doc-at-once.  Instead, it batch 
processes chunks of 2048 sequential docIDs per scorer.  This is a big 
performance gain, but it means that the sub scorers will all be positioned to 
the end of the 2048 doc chunk while the docs that matched within that chunk are 
collected.

I don't think we can easily fix this... likely the "fix" is to make it 
easy(ier) to force BQ to use BooleanScorer2 (which is doc-at-once)?  It is 
actually possible to force this, today, by having your collector return false 
from acceptDocsOutOfOrder...

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