OpenNLPSentenceBreakIterator.next(n) returns DONE instead of the end of the text when the n-th boundary is the last one, so next(1) differs from next() and a caller that steps with next(n) until DONE loses the final sentence group

Finding LFV-622Area: analysis / opennlp OpenNLPSentenceBreakIterator (java.text.BreakIterator implementation, next(int))Priority: lowImpact: minorNovelty: new

Finding page for LFV-622

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

What it shows

You set a text on an OpenNLPSentenceBreakIterator and call next(n) to jump n sentence boundaries, expecting the n-th boundary, as java.text.BreakIterator#next(int) promises ('Returns the nth boundary from the current boundary') and as n calls of next() give. When that boundary is the end of the text, next(n) returns DONE (-1) instead: with the model-free NLPSentenceDetectorOp on 'Whole text is one sentence.', next() from first() returns 27 but next(1) returns -1, and on the module's three-sentence test text (boundaries 0, 31, 59, 102) next(3) from first() returns -1 instead of 102 while next(2) correctly returns 59. The iterator is still moved to the end, so only the returned value is wrong; code that steps with next(n) until DONE loses the final sentence group.

The test shows that OpenNLPSentenceBreakIterator.next(1) returns DONE instead of the end of the text when that is the next boundary (no model file: new NLPSentenceDetectorOp()).

Expected vs actual

Expected next(1) from first() on "One sentence." to return 13, as next() does; actual -1 (DONE) on main, with -ea and -da.

Files

• src/org/apache/lucene/analysis/opennlp/TestSentenceBreakIteratorNextOne.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/analysis/common/build/libs/lucene-analysis-common-$V.jar
CP=$CP:$LUCENE/lucene/analysis/opennlp/build/libs/lucene-analysis-opennlp-$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.analysis.opennlp.TestSentenceBreakIteratorNextOne

The module(s) analysis-opennlp 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.