From ab47db4feef29f7f5739a21988c40a83755359f5 Mon Sep 17 00:00:00 2001
From: Ignacio Vera <ivera@apache.org>
Date: Wed, 23 Feb 2022 13:51:44 +0100
Subject: [PATCH] LUCENE-10437:  Improve error message in the Tessellator for
 polygon with all points collinear (#703)

Polygon tessellator throws a more informative error message when the provided polygon does not contain enough no-collinear points.
---
 lucene/CHANGES.txt                                       | 3 +++
 .../core/src/java/org/apache/lucene/geo/Tessellator.java | 6 ++++++
 .../src/test/org/apache/lucene/geo/TestTessellator.java  | 9 +++++++++
 3 files changed, 18 insertions(+)

diff --git a/lucene/CHANGES.txt b/lucene/CHANGES.txt
index cc89bc29fb6..50f8b18db8d 100644
--- a/lucene/CHANGES.txt
+++ b/lucene/CHANGES.txt
@@ -301,6 +301,9 @@ Other
 
 * LUCENE-10413: Make Ukrainian default stop words list available as a public getter. (Alan Woodward)
 
+* LUCENE-10437: Polygon tessellator throws a more informative error message when the provided polygon 
+  does not contain enough no-collinear points. (Ignacio Vera)
+
 ======================= Lucene 9.0.0 =======================
 
 New Features
diff --git a/lucene/core/src/java/org/apache/lucene/geo/Tessellator.java b/lucene/core/src/java/org/apache/lucene/geo/Tessellator.java
index 0990dc640b8..2ee19eaba96 100644
--- a/lucene/core/src/java/org/apache/lucene/geo/Tessellator.java
+++ b/lucene/core/src/java/org/apache/lucene/geo/Tessellator.java
@@ -102,6 +102,9 @@ public final class Tessellator {
     if (outerNode == null) {
       throw new IllegalArgumentException("Malformed shape detected in Tessellator!");
     }
+    if (outerNode == outerNode.next || outerNode == outerNode.next.next) {
+      throw new IllegalArgumentException("at least three non-collinear points required");
+    }
 
     // Determine if the specified list of points contains holes
     if (polygon.numHoles() > 0) {
@@ -154,6 +157,9 @@ public final class Tessellator {
     if (outerNode == null) {
       throw new IllegalArgumentException("Malformed shape detected in Tessellator!");
     }
+    if (outerNode == outerNode.next || outerNode == outerNode.next.next) {
+      throw new IllegalArgumentException("at least three non-collinear points required");
+    }
 
     // Determine if the specified list of points contains holes
     if (polygon.numHoles() > 0) {
diff --git a/lucene/core/src/test/org/apache/lucene/geo/TestTessellator.java b/lucene/core/src/test/org/apache/lucene/geo/TestTessellator.java
index 7162814ada2..c4d52d9eba7 100644
--- a/lucene/core/src/test/org/apache/lucene/geo/TestTessellator.java
+++ b/lucene/core/src/test/org/apache/lucene/geo/TestTessellator.java
@@ -169,6 +169,15 @@ public class TestTessellator extends LuceneTestCase {
     checkPolygon(wkt);
   }
 
+  public void testInvalidPolygonCollinear() throws Exception {
+    String wkt =
+        "POLYGON ((18.9401790919516 -33.9681188869036, 18.9401790919516 -33.9681188869036, 18.9401790919517 -33.9681188869036, 18.9401790919517 -33.9681188869036, 18.9401790919516 -33.9681188869036))";
+    Polygon polygon = (Polygon) SimpleWKTShapeParser.parse(wkt);
+    IllegalArgumentException ex =
+        expectThrows(IllegalArgumentException.class, () -> Tessellator.tessellate(polygon, true));
+    assertEquals("at least three non-collinear points required", ex.getMessage());
+  }
+
   public void testComplexPolygon01() throws Exception {
     String wkt =
         "POLYGON((58.8792517 54.9160937, 58.8762477 54.9154524, 58.8735011 54.9140217, 58.8726428 54.9127389, 58.8731146 54.9122507, 58.8741877 54.9120482, 58.8771918 54.9117028, 58.88011 54.913331, 58.8801175 54.9137036, 58.8805885 54.9143186, 58.8807109 54.9148604, 58.88011 54.915551, 58.8792517 54.9160937), "