DoubleMetaphoneFilter drops the alternate (secondary) code of a token whose text already equals its primary code, so 'JR' gets only JR while 'jr' gets JR and AR

Finding LFV-477Area: analysis / phonetic (DoubleMetaphoneFilter#incrementToken alternate-code branch; DoubleMetaphoneFilterFactory, SPI name doubleMetaphone)Priority: lowImpact: minorNovelty: new

Finding page for LFV-477

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

What it shows

You run text through DoubleMetaphoneFilter, documented as 'supporting secondary codes', and expect the token 'JR' to get the same codes as 'jr', because the encoder is case-insensitive and gives both the primary code JR and the alternate code AR. Instead, when a token's text already equals its own primary code, the filter keeps the token as the primary but never emits the alternate: 'jr' gives JR and AR, 'JR' gives only JR, in both inject modes and at every maxCodeLength where the token equals its code. A document containing 'JR' is then missed by a query that matches only through AR (executed: TermQuery AR matches the document 'jr' but not the document 'JR'), while matches through the primary code still work.

The test shows that DoubleMetaphoneFilter drops the alternate code of a token whose text already equals its primary code.

Expected vs actual

Expected new DoubleMetaphoneFilter(whitespaceMockTokenizer("JR"), 4, true) to emit [JR, AR] (the codes the encoder gives for both "JR" and "jr"); actual [JR], with -ea and -da.

Files

• src/org/apache/lucene/analysis/phonetic/TestDoubleMetaphoneFilterTokenEqualsCode.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/phonetic/build/libs/lucene-analysis-phonetic-$V.jar
CP=$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.phonetic.TestDoubleMetaphoneFilterTokenEqualsCode

The module(s) analysis-phonetic 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 2026-11-03. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.