Monitor with RegexpQueryHandler silently misses matching RegexpQuery queries, because the handler indexes each one under a fragment of its pattern text (for example 'cat|dog', 'colou' or '?mail') that matching terms do not contain

Finding LFV-322Area: monitor / presearcher (RegexpQueryHandler custom query handler)Priority: mediumImpact: silent wrong resultsNovelty: 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 build a Monitor whose presearcher uses RegexpQueryHandler, register ordinary regexp queries such as /cat|dog/, /colou*r/ or /e.?mail/, and match documents containing 'dog', 'color' or 'email'. You expect Monitor.match to report each query, because the regexp matches the document and the presearcher may only skip queries that cannot match. Instead the handler indexes each query under a piece of its pattern text cut only at '.', '*' and '?' ('cat|dog', 'colou', '?mail'), no document term contains that piece, so the query is never run and the match is silently lost.

Expected vs actual

• Expected: You expect Monitor.match to report each query, because the regexp matches the document and the presearcher may only skip queries that cannot match.
• Actual: The handler indexes each query under a piece of its pattern text cut only at '.', '*' and '?' ('cat|dog', 'colou', '?mail'), no document term contains that piece, so the query is never run and the match is silently lost.

Files

• src/org/apache/lucene/monitor/TestRegexpQueryHandlerOperators.java (JUnit test)

Run it

• Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
• Tested on Lucene main ea57360912ed (2026-10-24): 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/analysis/common/build/libs/lucene-analysis-common-$V.jar
CP=$CP:$LUCENE/lucene/memory/build/libs/lucene-memory-$V.jar
CP=$CP:$LUCENE/lucene/monitor/build/libs/lucene-monitor-$V.jar
CP=$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.monitor.TestRegexpQueryHandlerOperators

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.