Franco Callari created LUCENE-4314:
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Summary: The specification of DocIdSetIterator is needlessly
ambiguous.
Key: LUCENE-4314
URL: https://issues.apache.org/jira/browse/LUCENE-4314
Project: Lucene - Core
Issue Type: Improvement
Components: core/search
Affects Versions: 4.0-BETA, 3.6.1
Environment: All
Reporter: Franco Callari
Quoth Lucene at org.apache.lucene.search.DocIdSetIterator.advance:
"Advances to the first beyond (see NOTE below) the current whose document
number is greater than or equal to <i>target</i>. [...]
NOTE:</b> when <code> target ≤ current</code> implementations may opt
not to advance beyond their current {@link #docID()}."
However, the same specification contradictorily states that advance must behave
as if written:
int advance(int target) {
int doc;
while ((doc = nextDoc()) < target) {}
return doc;
}
That is, with at least one call to nextDoc() always made, unconditionally.
This ambiguity can lead to unexpected behavior. In fact, arguably every user of
this interface that does not test after every call whether the iterator has
exhausted AND has advanced is incorrect.
For example, I myself had one experimental implementation (coded against a
previous Lucene release) that caused an infinite loop in PhraseScorer.java
because, following the above specification, it "opted" not to move the iterator
when advance(target) was called with target < current.
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