Hunspell Dictionary cannot load SET ISO8859-10, or ISO8859-14 spelled any way except exactly "ISO8859-14" (UnsupportedCharsetException at load)

Finding LFV-928Area: analysis / hunspell (Dictionary SET encoding lookup)Priority: lowImpact: crashNovelty: 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 says SET ISO8859-10 (Latin-6, Nordic), a value the hunspell(5) man page lists among the possible SET values, or says ISO8859-14 (Latin-8, Celtic) spelled ISO-8859-14 or iso8859-14, and expect it to load: C Hunspell lower-cases the SET value and drops non-alphanumerics before its table lookup, and in Lucene every other listed ISO-8859 part loads in its hyphenated and lower-case spellings (ISO-8859-2, iso8859-2, ...). Instead the Dictionary constructor throws java.nio.charset.UnsupportedCharsetException, because Dictionary.getDecoder uses Lucene's own ISO8859_14Decoder only for the exact string "ISO8859-14" and otherwise calls Charset.forName, and the JDK has no ISO-8859-10 or ISO-8859-14 charset under any name. Spellings that do load decode every letter byte correctly, so nothing is silently wrong; the dictionary is refused.

The test shows that a Hunspell Dictionary whose affix file says SET ISO8859-10 (a value hunspell(5) lists) cannot be loaded.

Expected vs actual

Expected the dictionary to load (byte 0xBF read as U+014B); actual: the constructor throws UnsupportedCharsetException: ISO8859-10 from Charset.forName in Dictionary.getDecoder (expected SET ISO8859-10 to load, got java.nio.charset.UnsupportedCharsetException: ISO8859-10), with -ea and -da.

Files

src/org/apache/lucene/analysis/hunspell/TestSetEncodingIso8859_10.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.TestSetEncodingIso8859_10

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-set-encoding-names-vs-c-hunspell-reference

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.