Test framework: AssertingLeafCollector's DocIdStream wrapper ignores upTo in forEach(int upTo, IOIntConsumer) and passes every remaining doc to the consumer, so a collector that reads a stream in bounded steps under AssertingIndexSearcher (the default of LuceneTestCase.newSearcher) gets wrong per-step results with -da and a spurious 'exhausted' AssertionError on its next legal call with -ea

Finding LFV-664Area: test-framework / search: AssertingLeafCollector DocIdStream wrapper (AssertingIndexSearcher, bulk collection)Priority: lowImpact: minorNovelty: new

Finding page for LFV-664

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

What it shows

In a Lucene test you search with LuceneTestCase.newSearcher (an AssertingIndexSearcher) and a collector whose collect(DocIdStream) first calls stream.forEach(5, consumer) and then stream.count() for the rest, which the DocIdStream javadoc allows ('up to the given upTo exclusive ... It is not possible to iterate these doc IDs again later on'). You expect the split a plain IndexSearcher gives: docs 0-4 in the first step and docs 5-9 counted afterwards. Instead the test framework's wrapper calls the wrapped stream's unbounded forEach, so the first step also receives docs 5-9 and the second step gets nothing (with -da), and with -ea the nested wrapper then rejects the legal count() with AssertionError 'exhausted'.

The test shows that the test framework's AssertingLeafCollector wraps a DocIdStream, and the wrapper's forEach(int upTo, consumer) ignores upTo, so it passes every remaining doc to the consumer.

Expected vs actual

Expected: forEach(5, ...) over docs 0-9 sees [0, 1, 2, 3, 4]. Actual on main with -ea and with -da: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9].

Files

• src/org/apache/lucene/tests/search/TestAssertingLeafCollectorForEachUpTo.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=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$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.tests.search.TestAssertingLeafCollectorForEachUpTo

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