The org.apache.lucene.util.fst package overview's code examples do not compile on any release since 9.0.0: they call Util.getByOutput (removed in 9.0.0), the public FSTCompiler(INPUT_TYPE, Outputs) constructor (removed in 9.9.0) and the Util.Result fields input/output (private record components since 10.0.0) (documentation defect)

Finding LFV-1027Area: core / util/fst (package overview examples, package-info.java)Priority: lowImpact: minorNovelty: new

Finding page for LFV-1027

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

What it shows

The org.apache.lucene.util.fst package overview shows five usage examples (build an FST, look up by key, look up by value, iterate in sorted order, N-shortest paths) and the values they print. Copied into code on any release since 9.0.0 they do not compile: Util.getByOutput was removed in 9.0.0 (LUCENE-8638, which deleted the page's link to it but kept the code block), the public FSTCompiler(INPUT_TYPE, Outputs) constructor was removed in 9.9.0 (#12715; FSTCompiler.Builder is the API), and Util.Result became a record in 10.0.0 (#13328), so '.input' and '.output' are private and need input() and output(). With those three edits, dropping the lookup-by-value block because it has no replacement, the examples compile on main and print exactly the documented values, so only the javadoc is wrong.

Expected vs actual

Expected: The three examples compile: javac reports no errors.
Actual: 6 javac errors: the FSTCompiler constructor cannot be applied, getByOutput is not found, and input/output have private access in Util.Result (4 times).

Files

src/org/apache/lucene/util/fst/TestFstPackageExamples.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=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$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.util.fst.TestFstPackageExamples

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

TestFstPackageExamples.java

Formal models and scripts this finding's part of the hunt used: core-fst-package-examples-compile-and-print-documented-outputs

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.