FSTCompiler.compile()'s javadoc shows how to read back an FST written to a non-FSTReader DataOutput with 'fst = new FST<>(fstMetadata, dataInput, new OffHeapFSTStore())', but #13524 removed both the no-argument OffHeapFSTStore constructor and the 3-argument FST constructor in 9.12.0, so the example names APIs that no longer exist (documentation defect)
Finding LFV-988Area: core / util/fst (FSTCompiler.compile() javadoc example)Priority: lowImpact: minorNovelty: new
AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.
What it shows
The javadoc of FSTCompiler.compile() explains how to turn its result into an FST, and for an FST written to an ordinary IndexOutput it shows 'fst = new FST<>(fstMetadata, dataInput, new OffHeapFSTStore());'. Copied into code on any release since 9.12.0 this does not compile: OffHeapFSTStore now needs (IndexInput, offset, metadata) and the 3-argument FST constructor no longer exists, because #13524 changed both and left this javadoc as it was. The working form is FST.fromFSTReader(fstMetadata, new OffHeapFSTStore(indexInput, offset, fstMetadata)), with a null check because compile() returns null for an FST that accepts nothing; Lucene's own codecs and tests already use it, so only the javadoc is wrong.
The test shows that the off-heap example in the FSTCompiler.compile() javadoc (fst = new FST<>(fstMetadata, dataInput, new OffHeapFSTStore());, FSTCompiler.java:992-993) does not compile on main, because #13524 (9.12.0) removed the no-argument OffHeapFSTStore and the 3-argument FST constructors (a documentation defect).
Expected vs actual
Expected: the example compiles. Actual: javac errors in the FSTCompiler.compile() javadoc example expected:<[]> but was:<[constructor OffHeapFSTStore in class org.apache.lucene.util.fst.OffHeapFSTStore cannot be applied to given types; ... found: no arguments ...]> (-ea and -da).
Files
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=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar # test-framework dependencies (Maven Central)
CP=$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.TestFSTCompilerCompileJavadocExampleGradle 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).
Formal models and scripts this finding's part of the hunt used: javadoc-package-and-overview-examples-call-removed-apis-siblings-of-16904
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.