Classic QueryParser and MultiFieldQueryParser ignore an explicit phrase slop ("..."~N) when the phrase analyzes to a token graph (multi-word synonyms, WordDelimiterGraphFilter) or, for QueryParser, carries token boosts, and search with the default phraseSlop instead: fewer hits with the default slop 0, extra hits for an explicit ~0 when a larger default slop is set

Finding LFV-305Area: queryparser / classic QueryParser and MultiFieldQueryParser phrase slop (QueryParserBase.getFieldQuery(String,String,int), MultiFieldQueryParser.getFieldQuery and applySlop; core util/QueryBuilder graph and boosted phrases)Priority: mediumImpact: silent wrong resultsNovelty: known upstream

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

What it shows

You parse "guinea pig food"~1 with the classic QueryParser over an analyzer with a multi-word synonym 'guinea pig => cavy' and expect the documented proximity search, the words within one position of each other on every synonym path, as "pig food"~1 gives for a phrase without synonyms. Instead the parser analyzes the phrase with its default phraseSlop (0) and applies the explicit ~1 afterwards only to a top-level PhraseQuery or MultiPhraseQuery, so the BooleanQuery of per-path phrases that a token graph produces ('body:"cavy food" body:"guinea pig food"') and the BoostQuery that a token boost produces ('(body:"pig food")^2.0' for "pig|2.0 food"~1) keep slop 0, and 'my guinea pig dry food' is not found. The same root cause also over-matches: after setPhraseSlop(1), an explicit exact "guinea pig food"~0 is searched with slop 1 and returns extra documents; MultiFieldQueryParser has the graph defect in both directions but not the boost one, because its applySlop unwraps BoostQuery (since 9.6.0, #12196).

Expected vs actual

Expected: The test passes: it asserts the documented behaviour.
Actual: The parser analyzes the phrase with its default phraseSlop (0) and applies the explicit ~1 afterwards only to a top-level PhraseQuery or MultiPhraseQuery, so the BooleanQuery of per-path phrases that a token graph produces ('body:"cavy food" body:"guinea pig food"') and the BoostQuery that a token boost produces ('(body:"pig food")^2.0' for "pig|2.0 food"~1) keep slop 0, and 'my guinea pig dry food' is not found.

Files

src/org/apache/lucene/queryparser/classic/TestExplicitPhraseSlopDropped.java (JUnit test)
src/GraphPhraseSlopBisect.java (main() class)

Run it

Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
Tested on Lucene main ea57360912ed (2026-10-24): reproduced.
How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual); a main() class that exits non-zero, with an exception or AssertionError, is the finding reproducing.
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/analysis/common/build/libs/lucene-analysis-common-$V.jar
CP=$CP:$LUCENE/lucene/facet/build/libs/lucene-facet-$V.jar
CP=$CP:$LUCENE/lucene/queries/build/libs/lucene-queries-$V.jar
CP=$CP:$LUCENE/lucene/queryparser/build/libs/lucene-queryparser-$V.jar
CP=$CP:$LUCENE/lucene/sandbox/build/libs/lucene-sandbox-$V.jar
CP=$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.queryparser.classic.TestExplicitPhraseSlopDropped

# run 2: assertions on, seed DEADBEEF, default flags
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=DEADBEEF \
     -cp "classes:$CP" GraphPhraseSlopBisect

The module(s) facet also need their third-party runtime jars; ./gradlew -p lucene/<module> dependencies lists them.

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.