Surround query parser ignores a ^ weight written directly on the operand of a field prefix (title: lucene^3, title: body: lucene^3, body: or(a, b)^2), because FieldsQuery builds its operand with makeLuceneQueryFieldNoBoost

Finding LFV-686Area: queryparser / surround (FieldsQuery field prefixes and ^ weights)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-686

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 the surround query or(title: lucene^3, body: lucene), whose parser documents 'boosting (via ^)', and expect the title match to count three times, exactly like the same weight on the parenthesised field query or((title: lucene)^3, body: lucene). Instead the weight is kept on the parsed term (toString shows title:lucene^3.0), but FieldsQuery.makeLuceneQueryNoBoost builds its operand with makeLuceneQueryFieldNoBoost, so no BoostQuery is created: the title document scores 0.13076457 instead of 0.39229375, no more than the body-only match, which the weight was meant to outrank. Every weight on the direct operand of a field prefix is dropped (a term, an OR, a distance query, with one field or several); only scores and ranking change, never which documents match.

The test shows that the surround parser drops a ^ weight written on the operand of a field prefix: or(title: lucene^3, body: lucene) scores as if unweighted.

Expected vs actual

Expected: the score of or((title: lucene)^3, body: lucene), 0.39229375. Actual: 0.13076457 (one third of it: the ^3 is not applied), with -ea and -da.

Files

src/org/apache/lucene/queryparser/surround/query/TestSrndFieldPrefixOperandWeight.java (JUnit test)

Run it

Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
Recorded outcome of run 1 on Lucene main 645d4fe14a20: 1 test(s) run, 1 failed.
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 DEADBEEF
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.queryparser.surround.query.TestSrndFieldPrefixOperandWeight

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.