SegmentOrder.fromSort(numeric sort).reorder(reader) throws NullPointerException when a leaf's getCoreCacheHelper() returns null, which LeafReader documents as legal (ParallelCompositeReader over two or more readers, SortingCodecReader or MemoryIndex leaves, content-altering FilterLeafReaders)
Finding LFV-296Area: core / index: SegmentOrder (query-time segment re-ordering) and leaf core cache helpersPriority: lowImpact: crashNovelty: new
AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.
What it shows
You call SegmentOrder.fromSort(new Sort(new SortField("f", SortField.Type.LONG, true))).reorder(reader) to visit the segments with the highest f values first, on a reader whose leaves do not support caching, for example a ParallelCompositeReader over two DirectoryReaders with two segments each. You expect a re-ordered view, because reorder() accepts any IndexReader and LeafReader#getCoreCacheHelper documents null as a legal return value ('not suited for caching') that other consumers such as LRUQueryCache and QueryBitSetProducer simply skip. Instead reorder() throws NullPointerException at SegmentOrder.java:137, where the leaf comparator's memo calls reader.getCoreCacheHelper().getKey() without a null check.
The test shows that SegmentOrder.fromSort(LONG sort on f, descending).reorder(reader) on a MultiReader over two MemoryIndex readers throws NullPointerException; their leaves return null from getCoreCacheHelper(), which LeafReader documents as legal.
Expected vs actual
Expected: a reordered view with the f=2 leaf first; actual (-ea and -da): NPE at SegmentOrder.java:137 (reader.getCoreCacheHelper().getKey() without a null check), reported as an AssertionError that states both.
Files
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/memory/build/libs/lucene-memory-$V.jar
CP=$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.index.TestSegmentOrderNullCoreCacheHelperGradle 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.