SolrSynonymParser rejects a whole synonyms file because one line holds only spaces or tabs, although its javadoc says blank lines are comments (ParseException 'Invalid synonym rule at line N', every release since 3.4.0)

Finding LFV-548Area: analysis-common / synonym (SolrSynonymParser; SynonymGraphFilterFactory and SynonymFilterFactory, format solr)Priority: lowImpact: wrong errorNovelty: new

Finding page for LFV-548

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 synonyms file such as 'couch, sofa', then a line holding three spaces or a tab, then 'big, large', and expect it to parse, because the SolrSynonymParser javadoc says 'Blank lines and lines starting with '#' are comments'. Instead the whole file is rejected with ParseException 'Invalid synonym rule at line 2': the parser skips a line only when it has zero length (or starts with '#'), so the whitespace-only line is parsed as a rule whose single term trims to the empty string, which the analyzer step rejects. A truly empty line parses fine, and so did whitespace-only lines in the Solr loader this format came from before 3.4.

The test shows that SolrSynonymParser.parse rejects a synonyms file whose second line holds only three spaces ("couch, sofa\n \n"), although its class javadoc says blank lines are comments.

Expected vs actual

Expected: the line is skipped and parsing succeeds. Actual: ParseException: Invalid synonym rule at line 2, caused by IllegalArgumentException: term: was completely eliminated by analyzer.

Files

• src/org/apache/lucene/analysis/synonym/TestSolrSynonymParserWhitespaceOnlyLine.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.synonym.TestSolrSynonymParserWhitespaceOnlyLine

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.