[LUCENE-10680] UnifiedHighlighter's term extraction not working for some query rewrites

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Duplicate
• Component/s: modules/highlighter
• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Yannick Welsch
• Created: 17/Aug/22 08:21
• Updated: 18/Aug/22 16:30
• Resolved: 18/Aug/22 16:30

Description

UnifiedHighlighter rewrites the query against an empty index when extracting the terms from the query (see https://github.com/apache/lucene/blob/d5d6dc079395c47cd6d12dcce3bcfdd2c7d9dc63/lucene/highlighter/src/java/org/apache/lucene/search/uhighlight/UnifiedHighlighter.java#L149).

The rewrite step can unfortunately drop the terms that are to be extracted.

Take for example the boolean query "+field:value -ConstantScore(FieldExistsQuery [field=other_field])" when highlighting on "field".

The `FieldExistsQuery` rewrites on an empty index to a `MatchAllDocsQuery`, and as a `MUST_NOT` clause rewrites the overall boolean query to a `MatchNoDocsQuery`, dropping the `MUST` clause in the process, which means that the `field:value` term is not being extracted.