Improve error message when polygons contains twice the same point in no-consecutive position (#41051)

When a polygon contains a self-intersection due to have twice the same point in no-consecutive position, the polygon builder tries to split the polygon. During the split one of the polygons become invalid as it is not closed and an error is thrown which is not related to the real issue.

We detect this situation now and throw a more meaningful error.

server/src/main/java/org/elasticsearch/common/geo/builders/PolygonBuilder.java

@@ -406,7 +406,7 @@ public class PolygonBuilder extends ShapeBuilder<JtsGeometry, org.elasticsearch.
      * @param edges a list of edges to which all edges of the component will be added (could be <code>null</code>)
      * @return number of edges that belong to this component
      */
-    private static int component(final Edge edge, final int id, final ArrayList<Edge> edges) {
+    private static int component(final Edge edge, final int id, final ArrayList<Edge> edges, double[] partitionPoint) {
         // find a coordinate that is not part of the dateline
         Edge any = edge;
         while(any.coordinate.x == +DATELINE || any.coordinate.x == -DATELINE) {
@@ -438,6 +438,9 @@ public class PolygonBuilder extends ShapeBuilder<JtsGeometry, org.elasticsearch.
             if (edges != null) {
                 // found a closed loop - we have two connected components so we need to slice into two distinct components
                 if (visitedEdge.containsKey(current.coordinate)) {
+                    partitionPoint[0] = current.coordinate.x;
+                    partitionPoint[1] = current.coordinate.y;
+                    partitionPoint[2] = current.coordinate.z;
                     if (connectedComponents > 0 && current.next != edge) {
                         throw new InvalidShapeException("Shape contains more than one shared point");
                     }
@@ -479,10 +482,20 @@ public class PolygonBuilder extends ShapeBuilder<JtsGeometry, org.elasticsearch.
      * @param coordinates Array of coordinates to write the result to
      * @return the coordinates parameter
      */
-    private static Coordinate[] coordinates(Edge component, Coordinate[] coordinates) {
+    private static Coordinate[] coordinates(Edge component, Coordinate[] coordinates, double[] partitionPoint) {
         for (int i = 0; i < coordinates.length; i++) {
             coordinates[i] = (component = component.next).coordinate;
         }
+        // First and last coordinates must be equal
+        if (coordinates[0].equals(coordinates[coordinates.length - 1]) == false) {
+            if (partitionPoint[2] == Double.NaN) {
+                throw new InvalidShapeException("Self-intersection at or near point ["
+                    + partitionPoint[0] + "," + partitionPoint[1] + "]");
+            } else {
+                throw new InvalidShapeException("Self-intersection at or near point ["
+                    + partitionPoint[0] + "," + partitionPoint[1] + "," + partitionPoint[2] + "]");
+            }
+        }
         return coordinates;
     }
 
@@ -512,8 +525,9 @@ public class PolygonBuilder extends ShapeBuilder<JtsGeometry, org.elasticsearch.
         final Coordinate[][] points = new Coordinate[numHoles][];
 
         for (int i = 0; i < numHoles; i++) {
-            int length = component(holes[i], -(i+1), null); // mark as visited by inverting the sign
-            points[i] = coordinates(holes[i], new Coordinate[length+1]);
+            double[]  partitionPoint = new double[3];
+            int length = component(holes[i], -(i+1), null, partitionPoint); // mark as visited by inverting the sign
+            points[i] = coordinates(holes[i], new Coordinate[length+1], partitionPoint);
         }
 
         return points;
@@ -524,9 +538,10 @@ public class PolygonBuilder extends ShapeBuilder<JtsGeometry, org.elasticsearch.
 
         for (int i = 0; i < edges.length; i++) {
             if (edges[i].component >= 0) {
-                int length = component(edges[i], -(components.size()+numHoles+1), mainEdges);
+                double[]  partitionPoint = new double[3];
+                int length = component(edges[i], -(components.size()+numHoles+1), mainEdges, partitionPoint);
                 List<Coordinate[]> component = new ArrayList<>();
-                component.add(coordinates(edges[i], new Coordinate[length+1]));
+                component.add(coordinates(edges[i], new Coordinate[length+1], partitionPoint));
                 components.add(component);
             }
         }

server/src/test/java/org/elasticsearch/common/geo/ShapeBuilderTests.java

@@ -759,4 +759,22 @@ public class ShapeBuilderTests extends ESTestCase {
 
         assertEquals(expected, pb.toString());
     }
+
+    public void testInvalidSelfCrossingPolygon() {
+        PolygonBuilder builder = new PolygonBuilder(new CoordinatesBuilder()
+            .coordinate(0, 0)
+            .coordinate(0, 2)
+            .coordinate(1, 1.9)
+            .coordinate(0.5, 1.8)
+            .coordinate(1.5, 1.8)
+            .coordinate(1, 1.9)
+            .coordinate(2, 2)
+            .coordinate(2, 0)
+            .coordinate(0, 0)
+        );
+        Exception e = expectThrows(InvalidShapeException.class, () -> builder.close().buildS4J());
+        assertThat(e.getMessage(), containsString("Self-intersection at or near point ["));
+        e = expectThrows(InvalidShapeException.class, () -> builder.close().buildGeometry());
+        assertThat(e.getMessage(), containsString("Self-intersection at or near point ["));
+    }
 }