WikipediaTokenizer silently drops Chinese and Japanese text inside wiki markup (links, categories, headings, bold/italics, templates, citations, external-link labels): its grammar has a CJ token rule only for plain text, and every markup state matches ALPHANUM only

Finding LFV-708Area: analysis-common / wikipedia: WikipediaTokenizer (JFlex grammar lexical states, WikipediaTokenizerImpl.jflex)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-708

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 Chinese or Japanese wiki text with WikipediaTokenizer, for example '[[日本]]', '[[Category:日本]]', '== 日本 ==' or "x '''東京''' y", and expect the text inside the markup to become tokens, as it does for Latin and Korean text in the same markup ('[[Japan]]', '[[한국]]') and for Chinese/Japanese plain text ('日本' gives 日|<CJ> and 本|<CJ>). Instead every Chinese/Japanese character inside markup is skipped without an error: '[[日本]]', '[[Category:日本]]', '== 日本 ==' and '<ref>日本</ref>' give no token at all, '[http://example.org 日本]' gives only the URL, and "x '''東京''' y" gives x and y, with y typed bold. The cause is the grammar: its only CJ token rule is for plain text (WikipediaTokenizerImpl.jflex:201), while all nine markup lexical states have a token rule for ALPHANUM only and ignore every other character (:219-309), and the CJ character class is disjoint from ALPHANUM.

The test shows that WikipediaTokenizer drops Chinese/Japanese text inside wiki markup: the internal link [[日本]] gives no token, while [[Japan]] gives Japan.

Expected vs actual

Expected the terms to spell 日本; actual no token at all (expected:<[日本]> but was:<[]>), with -ea and -da.

Files

• src/org/apache/lucene/analysis/wikipedia/TestWikipediaTokenizerLinkCjk.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: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.wikipedia.TestWikipediaTokenizerLinkCjk

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.