[jira] [Created] (LUCENE-4961) Filters should return null if they don't accept documents

["Simon Willnauer (JIRA)" <ji...@apache.org>]

Simon Willnauer created LUCENE-4961:
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             Summary: Filters should return null if they don't accept documents
                 Key: LUCENE-4961
                 URL: https://issues.apache.org/jira/browse/LUCENE-4961
             Project: Lucene - Core
          Issue Type: Improvement
          Components: core/search
    Affects Versions: 4.2.1, 4.3
            Reporter: Simon Willnauer
             Fix For: 5.0, 4.4


Today we document that Filter#getDocIdSet can return null if it doesn't accept documents. Infact in the code we sometimes return null and sometimes return DocIdSet.EMPTY_DOCIDSET. Conceptually there is nothing wrong with that but apparently we are not applying our optimisations accordingly ie. some parts of the code check for the EMPTY_DOCIDSET and all check for null. this is also a source of potential bugs like in LUCENE-4940 and I think there are still problems in the ToChildBlock query.

Anyways, I think we should be consistent here about when to apply the optimisations and for the sake of caching in CachingWrapperFilter we should make the EMPTY_DOCIDSET and impl detail.

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