DisjunctionMaxQuery treats tie-breakers 0.0f and -0.0f as equal in equals() (IEEE ==) but hashes their raw bits in hashCode(), so two equal queries get different hash codes and the query cache, BooleanQuery clause sets and other hash-based structures treat them as different queries (since 1.9)

Finding LFV-1236Area: core / search: DisjunctionMaxQuery (equals and hashCode contract)Priority: lowImpact: minorNovelty: new

Finding page for LFV-1236

AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You build DisjunctionMaxQuery([f:x], 0.0f) and DisjunctionMaxQuery([f:x], -0.0f): equals returns true both ways (the constructor accepts -0.0f, and equalsTo compares the tie-breakers with ==, under which 0.0f == -0.0f), so by the Object#hashCode contract, which Query's javadoc requires so that QueryCache works, the two hash codes must be equal. Instead they differ by exactly 2^31, because hashCode adds Float.floatToIntBits(tieBreakerMultiplier), which is 0x00000000 for 0.0f and 0x80000000 for -0.0f. Hash-based structures therefore see two different queries: the query cache keeps a separate entry, a HashSet holds both and a BooleanQuery with both as FILTER clauses is not de-duplicated, while hits and scores stay the same.

Expected vs actual

Expected: equals and hashCode agree: equal queries have equal hash codes. Today a.equals(b) is true, so a.hashCode() must equal b.hashCode().
Actual: AssertionError: expected:<74785687> but was:<-2072697961> (through gradle, seed DEADBEEF; other run configurations give other values, always 2^31 apart): equal queries with different hash codes.

Files

src/org/apache/lucene/search/TestDisjunctionMaxQueryNegativeZeroTie.java (JUnit test)

Run it

Tested on Lucene main 5adff78bb168 (2026-11-02): 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, default flags
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.TestDisjunctionMaxQueryNegativeZeroTie

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).

Files shown on the finding page

TestDisjunctionMaxQueryNegativeZeroTie.java

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.