ComplexPhraseQueryParser: a phrase whose contents reduce to one clause that is not a bare term or multi-term query ("the beat*" with a stop-word analyzer, "+john", "john^2") parses, but searching it throws IllegalArgumentException instead of returning hits

Finding LFV-704Area: queryparser / complexPhrase: ComplexPhraseQueryParser (ComplexPhraseQuery.rewrite building a SpanNearQuery)Priority: mediumImpact: crashNovelty: known upstream

AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You parse a quoted phrase such as "the beat*" with ComplexPhraseQueryParser and an analyzer that removes the stop word 'the', or "+john", or "john^2", and search with it; single-clause complex phrases are supported ("beat*" and "john" work, upstream testSingleTermPhrase) and interior boosts are ignored by design (TestComplexPhraseQuery testBoosts), so you expect the hits of "beat*" or "john". Instead parse() succeeds and IndexSearcher.search throws IllegalArgumentException: when the contents are a one-clause BooleanQuery, ComplexPhraseQuery.rewrite builds a one-clause SpanNearQuery (ComplexPhraseQueryParser.java:331-333), which SpanNearQuery documents as invalid ('at least 2' clauses, SpanNearQuery.java:115), and ConjunctionSpans throws 'Less than 2 subSpans.size():1'; when the contents are a lone BoostQuery, rewrite throws 'Unknown query type "org.apache.lucene.search.BoostQuery" found in phrase query string' (:270-277).

Expected vs actual

• Expected: You expect the hits of "beat*" or "john".
• Actual: parse() succeeds and IndexSearcher.search throws IllegalArgumentException: when the contents are a one-clause BooleanQuery, ComplexPhraseQuery.rewrite builds a one-clause SpanNearQuery (ComplexPhraseQueryParser.java:331-333), which SpanNearQuery documents as invalid ('at least 2' clauses, SpanNearQuery.java:115), and ConjunctionSpans throws 'Less than 2 subSpans.size():1'; when the contents are a lone BoostQuery, rewrite throws 'Unknown query type "org.apache.lucene.search.BoostQuery" found in phrase query string' (:270-277).

Files

• src/org/apache/lucene/queryparser/complexPhrase/TestComplexPhraseSingleClauseContents.java (JUnit test)

Run it

• Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
• Tested on Lucene main a9779ef3c193 (2026-10-26): reproduced.
• How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual).
• Seeds: a rerun with the same seed replays the same random choices. Assertions off (-da -dsa -Dtests.asserts=false) is the production-like setting.

# Lucene checkout at the tested commit, built with: ./gradlew --no-daemon assemble   (JDK 25)
LUCENE=/path/to/lucene; V=12.0.0-SNAPSHOT
CP=$LUCENE/lucene/core/build/libs/lucene-core-$V.jar
CP=$CP:$LUCENE/lucene/codecs/build/libs/lucene-codecs-$V.jar
CP=$CP:$LUCENE/lucene/test-framework/build/libs/lucene-test-framework-$V.jar
CP=$CP:$LUCENE/lucene/facet/build/libs/lucene-facet-$V.jar
CP=$CP:$LUCENE/lucene/queries/build/libs/lucene-queries-$V.jar
CP=$CP:$LUCENE/lucene/queryparser/build/libs/lucene-queryparser-$V.jar
CP=$CP:$LUCENE/lucene/sandbox/build/libs/lucene-sandbox-$V.jar
CP=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar   # JUnit Platform console launcher (Maven Central)

javac -d classes -cp "$CP" $(find src -name '*.java')

# run 1: assertions on, seed C0A1E5CE
java -ea -esa -Xmx2g --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=C0A1E5CE \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.queryparser.complexPhrase.TestComplexPhraseSingleClauseContents

The module(s) facet also need their third-party runtime jars; ./gradlew -p lucene/<module> dependencies lists them.

Gradle alternative: copy the test into the matching module's src/test/ tree of the checkout and run ./gradlew -p lucene/<module> test --tests <class> -Ptests.seed=<seed> (add -Ptests.asserts=false for a run without assertions).

Feedback

Open an issue in lucene-ai-bug-hunt. Please do not open issues or pull requests in apache/lucene about this finding unless a Lucene committer agrees it should be filed.

Snapshot of 2026-11-03. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.