UnifiedHighlighter with maxNoHighlightPassages below -1 throws IllegalArgumentException 'Illegal Capacity' for every document with no match in the field, although the javadoc says any value below 0 falls back to maxPassages

Finding LFV-546Area: highlighter / UnifiedHighlighter no-match default summary (FieldHighlighter.highlightFieldForDoc maps only '== -1' to maxPassages; FieldHighlighter.getSummaryPassagesNoHighlight)Priority: lowImpact: wrong errorNovelty: new

Finding page for LFV-546

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 UnifiedHighlighter with withMaxNoHighlightPassages(-2), or any other negative value except -1, relying on the getMaxNoHighlightPassages javadoc: 'If it's less than 0 (the default) then this defaults to the maxPassages parameter given for each request.' For a document with no match in the field you expect the same default summary as with -1, for example 'First sentence. '. Instead FieldHighlighter maps only exactly -1 to maxPassages and passes -2 on to getSummaryPassagesNoHighlight, whose new ArrayList<>(Math.min(-2, 10)) throws IllegalArgumentException 'Illegal Capacity: -2', so the highlight call fails.

The test shows that UnifiedHighlighter built with withMaxNoHighlightPassages(-2) fails on a document that is a hit but has no match in the highlighted field.

Expected vs actual

Expected the default summary "First sentence. " (javadoc: any value below 0 defaults to maxPassages); actual IllegalArgumentException: Illegal Capacity: -2 from FieldHighlighter.getSummaryPassagesNoHighlight, with -ea and -da.

Files

• src/org/apache/lucene/search/uhighlight/TestNegativeMaxNoHighlightPassages.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/highlighter/build/libs/lucene-highlighter-$V.jar
CP=$CP:$LUCENE/lucene/memory/build/libs/lucene-memory-$V.jar
CP=$CP:$LUCENE/lucene/queries/build/libs/lucene-queries-$V.jar
CP=$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.search.uhighlight.TestNegativeMaxNoHighlightPassages

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 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.