Japanese completion suggester (JapaneseCompletionAnalyzer / JapaneseCompletionFilter): words with a small tsu before shi, chi or tsu (雑誌, 決して, マッチ, 三つ) are never suggested for their Hepburn or input-method spellings zasshi, kesshite, macchi/matchi, mittsu, because romaji_map.txt maps ッシ only to 'ssi', ッチ only to 'tti' and ッツ only to 'ttu', while the base rows シ/チ/ツ list shi/chi/tsu and the neighbouring rows ッシャ and ッチャ do double the consonant ('ssha', 'ccha')

Finding LFV-849Area: analysis / kuromoji completion romanization (romaji_map.txt read by KatakanaRomanizer; JapaneseCompletionFilter, JapaneseCompletionAnalyzer)Priority: mediumImpact: silent wrong resultsNovelty: new

Finding page for LFV-849

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

What it shows

You index 雑誌 ('magazine'), マッチ ('match') and 三つ ('three') in a document suggester with JapaneseCompletionAnalyzer, whose javadoc lists modified Hepburn among the supported romanizations, and expect typing 'zasshi', 'macchi' or 'mittsu' to suggest them, just as 'issho' suggests 一緒 and 'maccha' suggests 抹茶. Instead nothing is suggested: the bundled romaji_map.txt gives the small-tsu rows ッシ, ッチ and ッツ only the spellings 'ssi', 'tti' and 'ttu', although the base rows シ, チ, ツ list shi, chi, tsu and the neighbouring rows ッシャ and ッチャ list 'ssha' and 'ccha'. Only the Kunrei spellings (zassi, matti, mittu) find these words.

The test shows that the INDEX-mode JapaneseCompletionAnalyzer gives 雑誌 (ザッシ) only the Kunrei romaji zassi, never the modified-Hepburn zasshi (romaji_map.txt maps ッシ only to ssi), so typing "zasshi" cannot complete it.

Expected vs actual

Expected zasshi among the index-side tokens; actual [雑誌, zassi], with -ea and -da.

Files

Run it

# 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.TestCompletionSokuonHepburn

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).

Formal models and scripts this finding's part of the hunt used: kuromoji-completion-romaji-map-vs-hepburn-kunrei-wapuro-tables

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.