Hunspell spell() and suggest() throw AssertionError under -ea when a word ends with a CHECKCOMPOUNDPATTERN replacement whose beginchars are empty, because the compound check looks up a zero-length second part

Finding LFV-713Area: analysis / hunspell (Hunspell.spell and suggest compound checking, CHECKCOMPOUNDPATTERN replacements)Priority: lowImpact: minorNovelty: new

Finding page for LFV-713

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 a compound rule such as 'CHECKCOMPOUNDPATTERN o /X z' (a simplified compound form whose second part may begin with anything: hunspell(5) allows empty beginchars with a flag and an optional replacement) and call Hunspell.spell("foz"), and expect true or false; C Hunspell 1.3.2 and 1.7.2 both say false. Instead, with assertions enabled, spell() and suggest() throw java.lang.AssertionError from WordStorage.lookupWord ('assert length > 0'). The cause: checkCompoundPatternReplacements expands the final 'z' to 'o' plus empty beginchars and puts the break right after 'foo', but never checks that a second part remains, so checkCompoundsAfter looks up a second part of length 0; with -da that lookup finds nothing and spell() returns false for the repro.

The test shows that with -ea, Hunspell.spell("foz") throws for a dictionary with CHECKCOMPOUNDPATTERN o /X z (empty beginchars, replacement z), because expanding the final z leaves an empty second compound part that is then looked up.

Expected vs actual

Expected false (C Hunspell's answer, and Lucene's with -da); actual with -ea: AssertionError from assert length > 0 at WordStorage.lookupWord(WordStorage.java:107), reached from checkCompoundPatternReplacements. With -da the test passes (the claim is about -ea only).

Files

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

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.