FastVectorHighlighter with fragCharSize = Integer.MAX_VALUE (or any value above Integer.MAX_VALUE - spanStart) returns the whole field with only the first match highlighted: BaseFragListBuilder computes spanStart + fragCharSize in int, the sum wraps negative, and every later match is silently dropped (SimpleFragListBuilder, the default, and WeightedFragListBuilder)

Finding LFV-401Area: highlighter / vectorhighlight BaseFragListBuilder (FastVectorHighlighter, SimpleFragListBuilder, WeightedFragListBuilder)Priority: lowImpact: silent wrong resultsNovelty: known outside Lucene

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

What it shows

You index the field 'aaaaaaaaaaaaaaaaaaaa foo bbb foo ccc foo ddd' with term vectors (positions and offsets), search foo, and call FastVectorHighlighter.getBestFragments with fragCharSize = Integer.MAX_VALUE to get the whole field, expecting 'aaaaaaaaaaaaaaaaaaaa foo bbb foo ccc foo ddd', which fragCharSize 1000 or Integer.MAX_VALUE - 100 gives. Instead you get 'aaaaaaaaaaaaaaaaaaaa foo bbb foo ccc foo ddd', with no error: BaseFragListBuilder.createFieldFragList computes the fragment end as spanStart + fragCharSize in int, where spanStart is the first match's start minus the 6-char margin (15 here), so the sum wraps negative and the fragment closes at the end of the first match. The fragment is then re-centred to [0, Integer.MAX_VALUE), which covers the whole field, and every later match is discarded.

Expected vs actual

Expected: The test passes: it asserts the documented behaviour.
Actual: You get 'aaaaaaaaaaaaaaaaaaaa foo bbb foo ccc foo ddd', with no error: BaseFragListBuilder.createFieldFragList computes the fragment end as spanStart + fragCharSize in int, where spanStart is the first match's start minus the 6-char margin (15 here), so the sum wraps negative and the fragment closes at the end of the first match.

Files

src/org/apache/lucene/search/vectorhighlight/TestFragListBuilderHugeFragCharSize.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:$LUCENE/lucene/highlighter/build/libs/lucene-highlighter-$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 off (production-like), seed DEADBEEF
java -da -dsa -Dtests.asserts=false --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.vectorhighlight.TestFragListBuilderHugeFragCharSize

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).

Formal models and scripts this finding's part of the hunt used: overflow-at-scale-2

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.