Alan Woodward created LUCENE-8717:
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Summary: Handle stop words that appear at articulation points
Key: LUCENE-8717
URL: https://issues.apache.org/jira/browse/LUCENE-8717
Project: Lucene - Core
Issue Type: Bug
Reporter: Alan Woodward
Assignee: Alan Woodward
Our set of TokenFilters currently cannot handle the case where a multi-term
synonym starts with a stopword. This means that given a synonym file
containing the mapping "the walking dead => twd" and a standard english
stopword filter, QueryBuilder will produce incorrect queries.
The tricky part here is that our standard way of dealing with stopwords, which
is to just remove them entirely from the token stream and use a larger position
increment on subsequent tokens, doesn't work when the removed token also has a
position length greater than 1. There are various tricks you can do to
increment position length on the previous token, but this doesn't work if the
stopword is the first token in the token stream, or if there are multiple
stopwords in the side path.
Instead, I'd like to propose adding a new TermDeletedAttribute, which we only
use on tokens that should be removed from the stream but which hold necessary
information about the structure of the token graph. These tokens can then be
removed by GraphTokenStreamFiniteStrings at query time, and by
FlattenGraphFilter at index time.
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