KatakanaRomanizer.romanize(CharsRef) ignores CharsRef.offset, so a CharsRef that is a slice of a larger char[] is romanized from chars[0, length) instead of the slice (latent: Lucene's own JapaneseCompletionFilter always passes offset 0)
Finding LFV-341Area: analysis / kuromoji (KatakanaRomanizer in org.apache.lucene.analysis.ja.completion, the romaji helper of JapaneseCompletionFilter)Priority: lowImpact: minorNovelty: 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 call KatakanaRomanizer.getInstance().romanize(...) with a CharsRef that is a slice of a larger array, for example CharsRef.subSequence(2, 6) of 'ハシヤキュウ' (the slice 'ヤキュウ' at offset 2), and expect the romaji of the slice, [yakyuu], because CharsRef is documented as 'a slice (offset + length) into an existing char[]' and the same text at offset 0 gives [yakyuu]. Instead romanize reads chars[0, length), here 'ハシヤキ', and returns [hasiyaki, hashiyaki]; a slice at offset 1 of 'アトウキョウ' gives [atoukyo] instead of [toukyou], and one at offset 1 of 'xトウキョウt' gives [] instead of [toukyout]. There is no exception, with or without assertions, and Lucene's own JapaneseCompletionFilter is not affected because it always passes offset 0.
The test shows that KatakanaRomanizer.romanize(CharsRef) ignores CharsRef.offset: the slice トウキョウ at offset 1 of アトウキョウ is romanized from chars[0, 5) instead.
Expected vs actual
Expected [toukyou]; actual [atoukyo] (expected:<[toukyou]> but was:<[atoukyo]>), with -ea and -da; passes with the 2-line input.offset fix.
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: 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:$LUCENE/lucene/analysis/kuromoji/build/libs/lucene-analysis-kuromoji-$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.completion.TestKatakanaRomanizerCharsRefOffsetThe 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.