TermStates#equals compares only docFreq, so BooleanQuery still merges blended or fuzzy TermQuery clauses whose totalTermFreq differs, and similarities that read totalTermFreq then score them wrongly (the part of the #10309 fix, #12354, that was left out; main only)
Finding LFV-435Area: search / TermQuery equality and BooleanQuery clause de-duplication (blended and fuzzy TermStates)Priority: mediumImpact: silent wrong resultsNovelty: known upstream
AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.
What it shows
You OR two fuzzy queries, FuzzyQuery('aaaab', 1) and FuzzyQuery('baaaa', 1), which both expand to the indexed term 'aaaa', and search with LMDirichletSimilarity; you expect each document to score the sum of the two clause scores, as it does under BM25 and as #12354 ('Do not merge term queries with different docFreq', the fix of #10309) set out to restore. Instead the blended rewrite gives both TermQuery(t:aaaa) clauses the same docFreq (the max, 3) but different totalTermFreq (the sum, 4 and 8); TermStates#equals compares only docFreq, so BooleanQuery merges them into (t:aaaa)^1.5 with the first clause's statistics, and docs 0-2 score 0.0011983 instead of 0.00059916, while the same query with the clauses swapped (equal per BooleanQuery#equals) scores them 0.0.
Expected vs actual
- Expected: You expect each document to score the sum of the two clause scores, as it does under BM25 and as #12354 ('Do not merge term queries with different docFreq', the fix of #10309) set out to restore.
- Actual: The blended rewrite gives both TermQuery(t:aaaa) clauses the same docFreq (the max, 3) but different totalTermFreq (the sum, 4 and 8); TermStates#equals compares only docFreq, so BooleanQuery merges them into (t:aaaa)^1.5 with the first clause's statistics, and docs 0-2 score 0.0011983 instead of 0.00059916, while the same query with the clauses swapped (equal per BooleanQuery#equals) scores them 0.0.
Files
Run it
- Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
- Tested on Lucene main ea57360912ed (2026-10-24): reproduced.
- 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=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar # test-framework dependencies (Maven Central)
CP=$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.search.TestBlendedTermStatesMergeGradle 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.