Copying a ParallelLeafReader into an index (IndexWriter.addIndexes over SlowCodecReaderWrapper, or a merge whose OneMerge.wrapForMerge returns one) silently stores a later sub-reader's stored fields under another field's name: ParallelLeafReader.storedFields() lets each sub-reader visit with its own FieldInfo numbers while getFieldInfos() renumbers the fields, and StoredFieldsWriter.MergeVisitor skips its remap-by-name step when the numbers look aligned

Finding LFV-652Area: core / index (ParallelLeafReader stored fields x StoredFieldsWriter.MergeVisitor, on addIndexes and wrapForMerge copies)Priority: mediumImpact: data corruptionNovelty: new

Finding page for LFV-652

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

What it shows

You build two indexes in lockstep, as ParallelLeafReader requires (index A stores title='Lucene in Action', index B stores price='42'), wrap them in a ParallelLeafReader, which itself returns both fields correctly, and copy it into a new index with IndexWriter.addIndexes(SlowCodecReaderWrapper.wrap(reader)), expecting the copy to hold title and price. Instead the copy holds title='Lucene in Action' and title='42' and no price field, with no error and a clean CheckIndex: storedFields() lets B report price with B's own field number 0, the parallel reader's getFieldInfos() numbers price 1, and because the target's merged numbers equal the parallel reader's, the stored-fields merge skips its remap-by-name step and writes the value under number 0, which is title. A merge whose OneMerge.wrapForMerge adds a parallel index with stored fields behind each segment goes wrong the same way (a 'summary' value stored as a second 'id').

The test shows that IndexWriter#addIndexes(SlowCodecReaderWrapper.wrap(new ParallelLeafReader(a, b))) into a fresh index stores b's stored field under a's field name (a: title="Lucene in Action", b: price="42").

Expected vs actual

Expected the copy to have price=42; actual Document<stored<title:Lucene in Action> stored<title:42>> expected:<42> but was:<null>, with -ea and -da.

Files

• src/org/apache/lucene/index/TestParallelLeafReaderAddIndexesStoredFields.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.index.TestParallelLeafReaderAddIndexesStoredFields

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.