Tessellator.cureLocalIntersections adds each triangle it cuts off twice, so LatLonShape and XYShape index that triangle twice and the shape doc-values centroid counts its area twice

Finding LFV-792Area: geo / Tessellator cure step (polygon indexing for LatLonShape and XYShape, shape doc values)Priority: lowImpact: minorNovelty: new

Finding page for LFV-792

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

What it shows

You index a polygon with LatLonShape or XYShape (createIndexableFields or createDocValueField) and expect each triangle of its tessellation to be stored once. When the Tessellator's cure step (cureLocalIntersections) cuts off a triangle to repair a small local self-intersection, it appends that same triangle twice (two identical tessellation.add calls at Tessellator.java:890 and :892, left by LUCENE-8620 in 8.3.0), so the shape carries one extra indexed triangle, ShapeDocValuesField.numberOfTerms is one too high and getCentroid() counts that triangle's area twice; query results do not change. On its own the cure step fires only for self-crossing rings, which the javadoc excludes but the default checkSelfIntersections=false path accepts (for example POLYGON((6 3, 0 6, 4 0, 3 4, 5 1, 3 2, 6 3)), duplicated on every release from 8.3.0), and a valid polygon reaches it only when it already hits LFV-210 (a hole touching the shell), whose fix removes it.

The test shows that XYShape.createIndexableFields on the ring POLYGON((6 3, 0 6, 4 0, 3 4, 5 1, 3 2, 6 3)) (self-crossing, accepted by the default path) indexes the triangle cut off by Tessellator.cureLocalIntersections twice (TestTessellatorCureAddsTriangleTwice#testCuredTriangleIndexedOnce).

Expected vs actual

Expected: each triangle indexed once (3 fields); actual: 4 fields, 3 distinct (expected:<3> but was:<4>), with -ea and -da.

Files

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

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.