Fix flat polygons incorrectly containing intersecting geometries (#12022)

lucene/CHANGES.txt

@@ -195,6 +195,8 @@ Bug Fixes
 * GITHUB#11986: Fix algorithm that chooses the bridge between a polygon and a hole when there is
   common vertex. (Ignacio Vera)
 
+* GITHUB#12020: Fixes bug whereby very flat polygons can incorrectly contain intersecting geometries. (Craig Taverner)
+
 Optimizations
 ---------------------
 * GITHUB#11738: Optimize MultiTermQueryConstantScoreWrapper when a term is present that matches all

lucene/core/src/java/org/apache/lucene/document/ShapeField.java

@@ -376,6 +376,8 @@ public final class ShapeField {
       if (triangle.aX == triangle.cX && triangle.aY == triangle.cY) {
         triangle.type = DecodedTriangle.TYPE.POINT;
       } else {
+        // a and b are identical, remove ab, and merge bc and ca
+        triangle.ab = triangle.bc | triangle.ca;
         triangle.bX = triangle.cX;
         triangle.bY = triangle.cY;
         triangle.cX = triangle.aX;
@@ -383,8 +385,12 @@ public final class ShapeField {
         triangle.type = DecodedTriangle.TYPE.LINE;
       }
     } else if (triangle.aX == triangle.cX && triangle.aY == triangle.cY) {
+      // a and c are identical, remove ac, and merge ab and bc
+      triangle.ab = triangle.ab | triangle.bc;
       triangle.type = DecodedTriangle.TYPE.LINE;
     } else if (triangle.bX == triangle.cX && triangle.bY == triangle.cY) {
+      // b and c are identical, remove bc, and merge ab and ca
+      triangle.ab = triangle.ab | triangle.ca;
       triangle.cX = triangle.aX;
       triangle.cY = triangle.aY;
       triangle.type = DecodedTriangle.TYPE.LINE;

lucene/core/src/test/org/apache/lucene/document/TestLatLonShape.java

@@ -949,6 +949,34 @@ public class TestLatLonShape extends LuceneTestCase {
         LatLonShape.createIndexableFields(FIELDNAME, polygonInside));
   }
 
+  public void testFlatPolygonDoesNotContainIntersectingLine() throws IOException {
+    // Create line intersecting very flat polygon (but not contained)
+    double[] lons = new double[] {-0.001, -0.001, 0.001, 0.001, -0.001};
+    double[] lats = new double[] {1e-10, 0, -1e-10, 0, 1e-10};
+    Polygon polygon = new Polygon(lats, lons);
+    Line line = new Line(new double[] {0.0, 0.001}, new double[] {0.0, 0.0});
+
+    // Index the polygon
+    Directory dir = newDirectory();
+    RandomIndexWriter writer = new RandomIndexWriter(random(), dir);
+    Document document = new Document();
+    addPolygonsToDoc(FIELDNAME, document, polygon);
+    writer.addDocument(document);
+
+    // search
+    IndexReader r = writer.getReader();
+    writer.close();
+    IndexSearcher s = newSearcher(r);
+
+    // search for line within the polygon
+    Query q = LatLonShape.newGeometryQuery(FIELDNAME, QueryRelation.CONTAINS, line);
+    TopDocs topDocs = s.search(q, 1);
+    assertEquals("Polygon should not contain the line,", 0, topDocs.scoreDocs.length);
+
+    // cleanup
+    IOUtils.close(r, dir);
+  }
+
   private void doTestContainsGeometryCollectionIntersects(
       Field[] containsFields, Field[] intersectsField) throws IOException {
     Directory dir = newDirectory();