CachingCollector (and CachingCollectorManager) never calls LeafCollector#finish on the collector it wraps, nor on the second-pass collector when it replays cached scores, so finish-dependent collectors such as FacetsCollector silently report no hits

Finding LFV-180Area: search / CachingCollector first pass and score-caching replay (CachingCollector, CachingCollectorManager)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-180

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

What it shows

You wrap a FacetsCollector, or any collector that does its per-segment work in LeafCollector#finish, in a CachingCollector or CachingCollectorManager so you can run the query once and replay the hits later, or you replay a score-caching cache into such a collector, and you expect the same facet counts as a plain IndexSearcher search. Instead the collector reports no hits: CachingCollector's per-leaf wrapper overrides finish() for its own bookkeeping and never passes the call on, and the score-caching replay never calls finish() at all, although the no-score replay does. In the repro a query that matches 20 documents gives 0 matching docs, with no error unless assertions are enabled.

The test shows that CachingCollectorManager (cacheScores=true) never calls LeafCollector#finish on the wrapped first-pass FacetsCollector, nor on the FacetsCollector the scored cache is replayed into, so both report no hits (1-document index, MatchAllDocsQuery).

Expected vs actual

Expected hits [first pass, scored replay] = [1, 1], as a plain search gives; actual: [0, 0] (expected:<[1, 1]> but was:<[0, 0]>), with -ea and -da.

Files

• src/org/apache/lucene/facet/TestCachingCollectorFinish.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/facet/build/libs/lucene-facet-$V.jar
CP=$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.facet.TestCachingCollectorFinish

The module(s) facet also need their third-party runtime jars; ./gradlew -p lucene/<module> dependencies lists them.

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.