JapaneseNumberFilter and KoreanNumberFilter, meeting a stacked token after two or more numerals, drop the numerals after the first and keep the first one's text in the number buffer, where it is prepended to the next number (十一石二鳥と五 ends in 15 instead of 5) (known: #11398 / #11397, offsets only) (released since 6.0.0 / 8.2.0)

Finding LFV-1096Area: analysis / kuromoji and nori number filters (stacked tokens inside a number)Priority: lowImpact: silent wrong resultsNovelty: known upstream

AI-assisted finding, reproduced on Lucene main but not yet independently re-verified, and not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You run 十一石二鳥と五 through JapaneseTokenizer (search mode, compounds kept, the configuration of the upstream TestJapaneseNumberFilter) and JapaneseNumberFilter, and expect the separate number 五 at the end to normalize to 5, since stacked tokens are documented to be left untouched. Instead the filter re-emits 十, drops 一, keeps 十 in its number buffer and later emits 十 + 五 = 15; KoreanNumberFilter has the same code.

Expected vs actual

Expected: The test passes: it asserts the documented behaviour.
Actual: The filter re-emits 十, drops 一, keeps 十 in its number buffer and later emits 十 + 五 = 15; KoreanNumberFilter has the same code.

Files

src/org/apache/lucene/analysis/ja/TestJapaneseNumberFilterStackedTokenBuffer.java (JUnit test)

Run it

Tested on Lucene main e1faeba08bde (2026-11-02): reproduced.
Tested on Lucene main 645d4fe14a20 (2026-10-28): 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:$LUCENE/lucene/analysis/kuromoji/build/libs/lucene-analysis-kuromoji-$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.ja.TestJapaneseNumberFilterStackedTokenBuffer

The module(s) analysis-kuromoji 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 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.