SpanContainingQuery and SpanWithinQuery miss documents and spans when the little query's spans end out of order (for example a SpanOrQuery of a longer near clause and a shorter clause that can occur inside it): their single forward pass tests only the current little span (containing) or never goes back to a big span it skipped (within), so a later, shorter little span inside a big span is never tried

Finding LFV-909Area: queries / span queries (per-document lockstep of the ContainSpans subclasses in SpanContainingQuery and SpanWithinQuery)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-909

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 a' and search with SpanContainingQuery(big = SpanNear([a, b], slop 0), little = SpanOr(SpanNear([a, a], slop 5), b)): the big span 'a b' at [0,2) contains the little span 'b' at [1,2), so you expect a hit, and SpanWithinQuery with the same pair should match too. Instead both return nothing, because the little spans arrive sorted by start as [0,3) and then [1,2) (their ends go down, which the Spans contract allows), and each query's single forward pass gives up after testing only the longer little span [0,3): containing moves on to the next big span, within moves the big iterator past [0,2) and never comes back. The same happens in a sentence-scoped search for '(apple NEAR/5 pie) OR cake' on 'bos apple cake eos bos pie eos' (the 'cake' sentence is missed only because 'apple ... pie' crosses into the next sentence), so adding a word to a document or an OR alternative to the query can remove a hit; nothing extra is ever returned.

The test shows that SpanContainingQuery and SpanWithinQuery miss a match when the little query's spans end out of order: on 'a b a', little = spanOr(spanNear([a, a], 5), b) yields [0,3) then [1,2), and the shorter [1,2) inside big spanNear([a, b], 0) = [0,2) is never tested.

Expected vs actual

Expected both queries to match the document (containing=1 within=1); actual: neither does (containing=0 within=0), with -ea and -da.

Files

Run it

# 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 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.queries.spans.TestSpanContainUnorderedLittleEnds

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).

Formal models and scripts this finding's part of the hunt used: span-containing-within-lockstep-misses-nested-little-spans

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 2026-11-03. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.