Adrien Grand created LUCENE-6425:
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Summary: Move extractTerms to Weight
Key: LUCENE-6425
URL: https://issues.apache.org/jira/browse/LUCENE-6425
Project: Lucene - Core
Issue Type: Task
Reporter: Adrien Grand
Assignee: Adrien Grand
Priority: Minor
Today we have extractTerms on Query, but it is supposed to only be called after
the query has been specialized to a given IndexReader using
Query.rewrite(IndexReader) to allow some complex queries to replace terms
"matchers" with actual terms (eg. WildcardQuery).
However, we already have an abstraction for indexreader-specialized queries:
Weight. So I think it would make more sense to have extractTerms on Weight.
This would also remove the trap of calling extractTerms on a query which is not
rewritten yet.
Since Weights know about whether scores are needed or not, I also hope this
would help improve the extractTerms semantics. We currently have 2 use-cases
for extractTerms: distributed IDF and highlighting. While the former only cares
about terms which are used for scoring, it could make sense to highlight terms
that were used for matching, even if they did not contribute to the score (eg.
if wrapped in a ConstantScoreQuery or a BooleanQuery FILTER clause). So
highlighters could do searcher.createNormalizedWeight(query,
false).extractTerms(termSet) to get all terms that were used for matching the
query while distributed IDF would instead do
searcher.createNormalizedWeight(query, true).extractTerms(termSet) to get
scoring terms only.
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