Hunspell Dictionary throws a raw ArrayIndexOutOfBoundsException (or NullPointerException) instead of a descriptive error when a .dic entry uses an AM morphological alias number that the .aff file does not define, although the same mistake in the AF flag-alias table gets 'Bad flag alias number'
Finding LFV-1012Area: analysis-common / hunspell Dictionary parsing (AM morphological aliases)Priority: lowImpact: wrong errorNovelty: new
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 whose affix file has an AM table, for example 'AM 1' and 'AM po:noun', and whose .dic has an entry 'foo<TAB>2' that points at an alias the table does not define (or alias 0, or 'AM 2' with only one AM line). You expect a descriptive error, as for the same mistake in the flag-alias (AF) table, which gives IllegalArgumentException 'Bad flag alias number:2' (C Hunspell's source, the reference implementation, range-checks the index and keeps the word without morphological data; its 'bad morph. alias index' warning prints only in builds with HUNSPELL_WARNING_ON). Instead every Dictionary constructor fails with java.lang.ArrayIndexOutOfBoundsException 'Index 1 out of bounds for length 1' (or NullPointerException 'Cannot invoke "String.isBlank()" because "morphData" is null') from Dictionary.splitMorphData, which reads morphAliases[alias - 1] with no range check, and has done so since AM aliases were added in 4.10.0 (LUCENE-5778).
The test shows that a hunspell .dic entry pointing at an AM morphological alias the .aff does not define (alias 2, table of 1) makes Dictionary fail with a raw ArrayIndexOutOfBoundsException.
Expected vs actual
Expected: the word loads or the load fails with a descriptive ParseException/IllegalArgumentException (as an undefined AF alias gives Bad flag alias number); actual: ArrayIndexOutOfBoundsException: Index 1 out of bounds for length 1, with -ea and -da.
Files
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.TestDictionaryUndefinedMorphAliasGradle 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.