Intervals.atLeast stops early when the sub-iterator it just used runs out, so it loses minimal intervals and misses documents when nested; the same hand-over also lets a stale sub-iterator re-enter and return a non-minimal interval out of order

Finding LFV-286Area: queries / intervals (Intervals.atLeast: MinimumShouldMatchIntervalsSource)Priority: mediumImpact: silent wrong resultsNovelty: new

Finding page for LFV-286

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

What it shows

You index 'a b' and read the intervals of Intervals.atLeast(1, term a, term b), or search ordered(c, atLeast(1, a, b)) over 'a c b'; you expect [0,0] and [1,1], exactly what or(a, b) returns, and one hit. Instead atLeast returns only [0,0] and the ordered query finds nothing: when the sub-iterator just popped from atLeast's proximity queue has no further interval, nextInterval() does not pull a replacement from its background queue and ends, although the other source still has intervals. The same hand-over never advances waiting sub-iterators past the current start, so atLeast(1, b, phrase(a, b)) on 'a b b' returns [1,1] then [0,1] (out of order, and [0,1] contains [1,1]) and loses [2,2].

The test shows that Intervals.atLeast(1, term a, term b) over the text "a b" stops after the first interval (TestAtLeastOneLosesLastInterval#testAtLeastOneOfTwoTerms).

Expected vs actual

Expected intervals [0,0] and [1,1] (what or(a, b) returns); actual only [0,0], with -ea and -da.

Files

• src/org/apache/lucene/queries/intervals/TestAtLeastOneLosesLastInterval.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/queries/build/libs/lucene-queries-$V.jar
CP=$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 5EED0286
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=5EED0286 \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.queries.intervals.TestAtLeastOneLosesLastInterval

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.