With an index sort, a document whose sort field is indexed without doc values (for example only as a StringField) is accepted by addDocument, and the next flush throws IllegalStateException and closes the IndexWriter, losing every uncommitted document (since 8.6.0)

Finding LFV-760Area: index / index sorting (IndexingChain index-sort field validation and flush-time sort)Priority: lowImpact: crashNovelty: new

Finding page for LFV-760

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

What it shows

You configure an index sort on a field, for example new Sort(new SortField("sort", SortField.Type.STRING)), and add a document that carries that field only as a StringField, without the SortedDocValuesField that sorting reads, before any committed document has the field. You expect addDocument to reject the document up front, as it has rejected a doc-values field of the wrong type since LUCENE-8441 (7.5.0), or the field to count as missing. Instead addDocument accepts it, and the next flush or commit throws IllegalStateException 'unexpected docvalues type NONE for field 'sort' (expected=SORTED). Re-index with correct docvalues type.' and closes the IndexWriter, so every document added since the last commit is lost.

The test shows that with an index sort on sort, a document that has sort only as a StringField (no doc values) is accepted by addDocument, and the next commit throws and closes the IndexWriter (losing every uncommitted document).

Expected vs actual

Expected addDocument to reject the document or the commit to succeed; actual on main: commit throws IllegalStateException: unexpected docvalues type NONE for field 'sort' (expected=SORTED) and writer open=false, with -ea and -da.

Files

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

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.