Nori's DictionaryBuilder rejects a left context id of 8192 or more but silently accepts such a right context id, which does not round-trip through the compiled format, so the compiled dictionary returns a wrapped right id (changing segmentation) or makes KoreanTokenizer throw IndexOutOfBoundsException

Finding LFV-710Area: analysis / nori system dictionary builder (DictionaryBuilder, TokenInfoDictionaryEntryWriter; custom system dictionaries)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-710

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

What it shows

You compile a custom nori system dictionary with DictionaryBuilder from MeCab-format sources in which a lexicon row (or an unk.def row) has right context id 16385, with a matrix.def that declares 16386 right ids, and expect the row either to be rejected, as a left id of 8192 is ('leftId >= 8192'), or to read back as 16385. Instead the builder accepts it and packs the id into a 14-bit field without any check (TokenInfoDictionaryEntryWriter.java:137), so Dictionary.getRightId returns 1 and KoreanTokenizer uses the connection costs of right id 1: in the repro '가나다' is split [가나, 다] instead of [가, 나다]. A right id in [8192, 16383] decodes to about 1.07 billion, and tokenizing any text that contains the word throws IndexOutOfBoundsException from ConnectionCosts.get.

The test shows that nori's DictionaryBuilder accepts a lexicon row with right context id 16385 (it rejects a left id of 8192) and the compiled dictionary reads it back wrapped to 14 bits.

Expected vs actual

Expected the build to reject the row or getRightId to return 16385; actual 1 (expected:<16385> but was:<1>), with -ea and -da.

Files

• src/org/apache/lucene/analysis/ko/dict/TestNoriBuilderRightIdLimit.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:$LUCENE/lucene/analysis/nori/build/libs/lucene-analysis-nori-$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.ko.dict.TestNoriBuilderRightIdLimit

The module(s) analysis-nori 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).

Formal models and scripts this finding's part of the hunt used: cjk-compiled-dictionary-source-round-trip

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.