Hunspell spell() accepts two-word flag-based compounds (COMPOUNDFLAG or COMPOUNDBEGIN/END) when COMPOUNDWORDMAX is 1 (or 0, which the parser clamps to 1), because the word-count check skips the first compound part

Finding LFV-724Area: analysis / hunspell (Hunspell.spell compound checking, COMPOUNDWORDMAX)Priority: lowImpact: minorNovelty: new

Finding page for LFV-724

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

What it shows

You load a Hunspell dictionary with 'COMPOUNDFLAG C', 'COMPOUNDMIN 1', 'COMPOUNDWORDMAX 1' and the words foo/C and bar/C, call Hunspell.spell("foobar"), and expect false: hunspell(5) defines COMPOUNDWORDMAX as the maximum word count in a compound, and C Hunspell 1.3.2 and 1.7.2 reject foobar. Instead Lucene returns true, with and without -ea; COMPOUNDWORDMAX 0, which the parser clamps to 1, behaves the same, while with COMPOUNDWORDMAX 2 Lucene correctly accepts foobar and rejects foobarfoo. The cause: checkCompounds counts parts only when a previous part exists ('prev != null && prev.index > compoundMax - 2'), so the first part is never counted and checkCompoundsAfter accepts first part + last part at any limit; the original LUCENE-9699 check, which did enforce a limit of 1, was lost in a 2021 refactoring (LUCENE-9729).

The test shows that with COMPOUNDFLAG C, COMPOUNDMIN 1, COMPOUNDWORDMAX 1 and the words foo/C, bar/C, Hunspell.spell("foobar") accepts the 2-word compound.

Expected vs actual

Expected: false (hunspell(5): COMPOUNDWORDMAX is the maximum word count in a compound; C Hunspell rejects it); actual (-ea and -da): true, because checkCompounds never counts the first part.

Files

• src/org/apache/lucene/analysis/hunspell/TestCompoundWordMaxOne.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.hunspell.TestCompoundWordMaxOne

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.