Grouping collectors never ask for scores on behalf of their group selector, so DoubleRangeGroupSelector or LongRangeGroupSelector over a score-dependent source (e.g. DoubleValuesSource.SCORES) groups every hit by the placeholder score of a non-scoring search (0 in every repro) when no sort or reducer needs scores, or when AllGroups/AllGroupHeads runs alone (since 8.6.0)

Finding LFV-884Area: grouping / GroupSelector score needs (FirstPass, SecondPass/TopGroups, AllGroups, AllGroupHeads collector score modes)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-884

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

What it shows

You group hits into score ranges, for example with new DoubleRangeGroupSelector(DoubleValuesSource.SCORES, new DoubleRangeFactory(0, 1, 10)), and sort the groups by a field, expecting each hit in the range of its own score, which is what the same search returns with the default relevance group sort (three ranges, [1,2) = {0, 3}, [2,3) = {1}, [3,4) = {2, 4}, in the repro). Instead GroupingSearch returns one empty group [0,1) (LongRangeGroupSelector: LongRange(0, 1)), and AllGroupsCollectorManager on its own reports one range instead of three, because the grouping collectors take their ScoreMode only from their sorts or reducer, so the query runs without scores and the selector, which reads the collector's Scorable through DoubleValuesSource.fromScorer, sees the placeholder score 0 for every hit. GroupSelector has no way to say that it needs scores; a GroupSelector#needsScores() hook (true for the range selectors when their source needs scores), ORed into the four collectors' score modes, fixes it.

The test shows that grouping by DoubleRangeGroupSelector(DoubleValuesSource.SCORES, ...) with a field group sort runs the first pass without scores, so every hit falls in the range of score 0.

Expected vs actual

Expected groups [DoubleRange(1.0, 2.0), DoubleRange(2.0, 3.0)] for two hits that score 1 and 2; actual [DoubleRange(0.0, 1.0)], 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/grouping/build/libs/lucene-grouping-$V.jar
CP=$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.search.grouping.TestScoreRangeGroupingFieldGroupSort

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.