WordDelimiterGraphFilter drops the hole of a swallowed last token (a punctuation-only token such as the '--' in 'foo --', or a token whose parts the flags all switch off) and any stop-word hole that token carries, because it has no end() override, so the final position increment is 0 and the next value of a multi-valued field starts too early (released since 6.5.0)

Finding LFV-354Area: analysis / WordDelimiterGraphFilter final position increment (end of stream, accumPosInc)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-354

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

What it shows

You analyse 'foo --' (or 'foo the --' behind a StopFilter) with a whitespace tokenizer and WordDelimiterGraphFilter at its default flags, and expect the swallowed punctuation-only token to leave a hole that end() reports as a final position increment of 1 (2 with the stop word), as the filter does mid-stream ('foo -- bar' puts bar at +2, which upstream tests assert) and as StopFilter does for 'foo the'. Instead the filter keeps that hole in an internal accumulator that only a later emitted token applies and has no end() override, so the final increment is 0. In a multi-valued field with the default gap 0 the next value 'bar' then lands at position 1 instead of 2: PhraseQuery(foo, bar) matches the values 'foo --' | 'bar' while the StopFilter control 'foo the' | 'bar' does not, and the phrase QueryBuilder builds for 'foo -- bar' matches the single value 'foo -- bar' but not the two values (both executed).

The test shows that WordDelimiterGraphFilter (factory default flags, after a WhitespaceTokenizer) drops the hole of a swallowed trailing punctuation-only token: for foo -- its end() reports no final position increment, although the same token leaves a hole mid-stream.

Expected vs actual

Expected finalPosInc 1; actual 0 (finalPosInc expected:<1> but was:<0>), with -ea and -da.

Files

Run it

# 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/analysis/common/build/libs/lucene-analysis-common-$V.jar
CP=$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.analysis.miscellaneous.TestWordDelimiterGraphFilterTrailingHole

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.