UpgradeIndexMergePolicy's class javadoc example calls new IndexWriterConfig(Version.LUCENE_XX, new KeywordAnalyzer()), a constructor removed in 5.0.0 (LUCENE-5871), so the example does not compile with any version constant (documentation defect)

Finding LFV-1021Area: core / index (UpgradeIndexMergePolicy class javadoc example)Priority: lowImpact: minorNovelty: new

Finding page for LFV-1021

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

What it shows

The UpgradeIndexMergePolicy javadoc says that for a fully customizable upgrade you can use this policy like any other merge policy and call forceMerge, and shows five lines that start with new IndexWriterConfig(Version.LUCENE_XX, new KeywordAnalyzer()). That two-argument constructor was removed in 5.0.0 (LUCENE-5871), so the example does not compile on any release since then, whatever real version constant you put in for the LUCENE_XX placeholder. With new IndexWriterConfig(new KeywordAnalyzer()) the same example compiles and, run on a 10.0.0 index, rewrites every segment to the current version and keeps every live document, so only the javadoc is wrong.

Expected vs actual

Expected: The copied example compiles (with a real version in for LUCENE_XX).
Actual: One javac error, no suitable constructor found for IndexWriterConfig(Version,KeywordAnalyzer), with assertions on and off, on main and on the 10.6.0 jars.

Files

src/org/apache/lucene/index/TestUpgradeIndexMergePolicyJavadocExample.java (JUnit test)

Run it

Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
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: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.TestUpgradeIndexMergePolicyJavadocExample

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).

Files shown on the finding page

TestUpgradeIndexMergePolicyJavadocExample.java

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.