AnalyzingSuggester and FuzzySuggester count skipped duplicate copies of a surface form toward maxSurfaceFormsPerAnalyzedForm, so distinct lower-weighted surface forms are silently dropped

Finding LFV-248Area: suggest / analyzing suggester (AnalyzingSuggester.build, inherited by FuzzySuggester)Priority: lowImpact: silent wrong resultsNovelty: new

Finding page for LFV-248

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 an AnalyzingSuggester or FuzzySuggester from entries in which one text repeats, for example 256 documents with 'Apple iPhone' and one with 'apple iphone', which a lowercasing analyzer maps to the same analyzed form, and you expect both surface forms back, because maxSurfaceFormsPerAnalyzedForm (default 256) is documented as the 'maximum number of surface forms to keep for a single analyzed form' and repeated copies are documented as removed. build() increments its per-analyzed-form counter and applies the limit before it checks whether the surface form was already seen, so every skipped copy still uses up a slot: lookup('apple ip') returns only [Apple iPhone], and with a limit of 2 the entries a/10, a/5, A/3 give [a/10] instead of [a/10, A/3]. With 255 copies, or without the repeated copy, both forms are returned.

The test shows that AnalyzingSuggester with maxSurfaceFormsPerAnalyzedForm=2 and the entries a/10, a/5, A/3 (a lowercasing analyzer maps all three to a) counts the skipped duplicate copy a/5 toward the limit and drops the distinct surface form A/3.

Expected vs actual

Expected: lookup("a") = [a/10, A/3]. Actual: [a/10], with -ea and -da.

Files

• src/org/apache/lucene/search/suggest/analyzing/TestAnalyzingSuggesterDuplicateCopyTakesSlot.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=$CP:$LUCENE/lucene/analysis/common/build/libs/lucene-analysis-common-$V.jar
CP=$CP:$LUCENE/lucene/suggest/build/libs/lucene-suggest-$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.search.suggest.analyzing.TestAnalyzingSuggesterDuplicateCopyTakesSlot

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.