Hunspell: a bracket or dot affix condition with fewer character patterns than the strip is checked against the wrong end of the strip (a suffix rule at the strip's start, a prefix rule at its end), so the rule never applies when it should, or always applies when it should not

Finding LFV-374Area: analysis / hunspell (affix conditions: Dictionary loading, Hunspell.spell/getRoots, Stemmer and HunspellStemFilter)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-374

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 the suffix rule 'SFX A abc d [c]' (strip abc, add d, condition [c]) on the root xabc and expect the condition to be tested where Hunspell lines it up, at the end of the root, which for a condition shorter than the strip is the end of the strip: xd should be a correct word with stem xabc and 'SFX A abc e [a]' should never apply, as C Hunspell 1.3.2 answers and as Lucene itself answers when the same condition is written as the literal c. Instead Lucene rejects xd and accepts xe as a form of xabc, and the prefix rules 'PFX B abc d [a]' and 'PFX B abc e [c]' on the root abcx are reversed the same way (dx rejected, ex accepted); spell, getRoots and HunspellStemFilter give these wrong verdicts and stems with no error. The cause is AffixCondition.compile: for a condition with [ ] or . and no more character patterns than the strip, it decides the rule once at load by matching the strip against 'kind == PREFIX ? ".*" + condition : condition + ".*"', which tests the strip's start for SFX and its end for PFX, the two templates swapped between the kinds.

The test shows that a Hunspell suffix rule whose bracket condition is shorter than its strip is checked against the start of the strip instead of the end of the root (SFX A abc d [c] on root xabc).

Expected vs actual

Expected spell("xd") to be true (xabc ends in c, and the same rule with the literal condition c accepts it); actual: false (expected:<true> but was:<false>), with -ea and -da.

Files

Run it

# 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.TestAffixConditionShorterThanStrip

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).

Formal models and scripts this finding's part of the hunt used: hunspell

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.