JapaneseTokenizer and KoreanTokenizer with discardPunctuation=true (the default) keep punctuation and symbols outside the BMP (U+10100, U+1E95E, emoji such as U+1F600) as tokens, because isPunctuation classifies a single UTF-16 unit (the high surrogate), while BMP characters of the same general category are dropped (released since 3.6.0 and 7.4.0)
Finding LFV-749Area: analysis / kuromoji and nori Viterbi tokenizers, discardPunctuation (ja.ViterbiNBest.isPunctuation and its three discard sites, ko.Viterbi.shouldFilterToken)Priority: lowImpact: silent wrong resultsNovelty: new
AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.
What it shows
You tokenize '日本 😀 日本' or '한국 𐄀 한국' (U+1F600, U+10100) with JapaneseTokenizer or KoreanTokenizer and discardPunctuation=true, the default, and expect [日本, 日本] and [한국, 한국], because the javadoc says punctuation tokens are dropped and both tokenizers drop every BMP character of the same Unicode general category (Po U+3001, So U+2605, Sm U+2207). Instead the supplementary character is kept as a token ([日本, 😀, 日本], [한국, 𐄀, 한국]): isPunctuation(char) calls Character.getType on the high surrogate alone, whose type is SURROGATE, so the discard test at the token start never sees the real category. No error is raised; the default KoreanAnalyzer indexes the extra token, and the default JapaneseAnalyzer removes it only later, through its part-of-speech stop filter, which leaves a position gap.
JapaneseTokenizer and KoreanTokenizer with discardPunctuation=true keep the supplementary-plane punctuation character U+10100 (General_Category Po) as a token (one test per tokenizer).
Expected vs actual
Expected [日本, 日本] / [한국, 한국] for 日本 U+10100 日本 / 한국 U+10100 한국; actual [日本, U+10100, 日本] / [한국, U+10100, 한국].
Files
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: 2 test(s) run, 2 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/kuromoji/build/libs/lucene-analysis-kuromoji-$V.jar
CP=$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.TestDiscardSupplementaryPunctuationThe module(s) analysis-kuromoji, 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).
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.