Operations.complement and minus give a wrong, non-deterministic result for an automaton with an arc ending at Integer.MAX_VALUE, because totalize computes t.max + 1 in int and the wrap adds a dead-state arc that overlaps the real arc

Finding LFV-1167Area: util / automaton (Operations.totalize, used by Operations.complement and Operations.minus)Priority: lowImpact: minorNovelty: new

Finding page for LFV-1167

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 Automata.makeCharRange('a', Integer.MAX_VALUE), which accepts every one-code-point word from "a" upward, and take its complement with Operations.complement; you expect a deterministic automaton (as the javadoc promises) that rejects "a". Instead the complement accepts "a" and is not deterministic, with no error: totalize, which complement uses to send every missing label to a dead state, computes t.max + 1 in int, the sum wraps to Integer.MIN_VALUE, so it also adds a dead-state arc over the whole code-point range on top of the real arc, and that dead state becomes accepting in the complement. Operations.minus, which subtracts through complement, likewise keeps words it should remove.

Expected vs actual

Expected: The complement rejects "a": its intersection with makeString("a") is empty.
Actual: It accepts "a": java.lang.AssertionError at line 29, assertions on and off.

Files

src/org/apache/lucene/util/automaton/TestComplementOfRangeEndingAtMaxValue.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
java -ea -esa -Xmx1g --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.util.automaton.TestComplementOfRangeEndingAtMaxValue

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

TestComplementOfRangeEndingAtMaxValue.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.