ICUTransformFilterFactory accepts direction="Forward" or "FORWARD" without error (it validates the value case-insensitively) but then builds the reverse transliterator, so every token is silently transformed the wrong way (regression of LUCENE-4877, since 4.3.0)

Finding LFV-1119Area: analysis / icu (ICUTransformFilterFactory: 'direction' parameter parsing through AbstractAnalysisFactory.get(..., caseSensitive=false))Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-1119

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

What it shows

You build an ICUTransformFilterFactory with id=Cyrillic-Latin and direction="Forward", which the factory accepts because it checks direction case-insensitively, and analyze 'Российская Федерация'. You expect the forward Cyrillic-Latin transliteration [Rossijskaâ, Federaciâ], as with direction="forward". You get the Cyrillic tokens back unchanged, with no error: the validation hands back the caller's own spelling, the factory then tests "forward".equals(direction), and every accepted spelling other than exact lower-case 'forward' builds the reverse (Latin-Cyrillic) transliterator.

Expected vs actual

• Expected: Federaciâ, the forward Cyrillic-to-Latin result, as with direction="forward".
• Actual: term 0 expected:<[Federaciâ]> but was:<[Федерация]>: the reverse transform ran; the same with assertions off.

Files

• src/org/apache/lucene/analysis/icu/TestICUTransformForwardDirection.java (JUnit test)

Run it

• Tested on Lucene main 5adff78bb168 (2026-11-02): 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/icu/build/libs/lucene-analysis-icu-$V.jar
CP=$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, default flags
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.icu.TestICUTransformForwardDirection

The module(s) analysis-icu 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).

Files shown on the finding page

• TestICUTransformForwardDirection.java

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.