SynonymGraphFilterFactory and SynonymFilterFactory keep a UTF-8 byte order mark at the start of a synonyms file, so the file's first rule silently stops working and a commented-out first line that contains a comma becomes a live rule
Finding LFV-956Area: analysis-common / synonym file loading (SynonymGraphFilterFactory and the deprecated SynonymFilterFactory loadSynonyms -> SolrSynonymParser, WordnetSynonymParser)Priority: lowImpact: silent wrong resultsNovelty: 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 configure SynonymGraphFilterFactory (or SynonymFilterFactory) with a synonyms file that an editor saved as UTF-8 with a byte order mark (bytes EF BB BF) and expect the same rules as from the file without the mark, because Lucene's shared resource-line loader skips a leading BOM for the word-list factories that read through it (WordlistLoader.getLines, 'skip initial bom marker', SOLR-1865) and the synonym factory itself skipped it until 3.4.0. Instead the factory decodes the file with its own UTF-8 reader and SolrSynonymParser keeps U+FEFF glued to the first line: with the first rule 'foo, bar' the text 'foo' is no longer expanded (and 'bar' gains the invisible synonym '\uFEFFfoo'), a first rule 'baz => qux' never fires, and a first line '#couch, sofa' is no longer a comment, so 'sofa' expands to '\uFEFF#couch'. In WordNet format the fixed-column synset id (substring(2, 11)) is shifted by one character, so the first word ends up in a synset of its own; nothing reports an error.
The test shows that SynonymGraphFilterFactory with a synonyms file that starts with a UTF-8 byte order mark ("\uFEFFfoo, bar\n") silently drops the first rule.
Expected vs actual
Expected "foo" to expand to [bar, foo], as without the mark; actual: [foo] (term 0 expected:<[bar]> but was:<[foo]>), 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.synonym.TestSynonymGraphFilterFactoryUtf8BomGradle 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.