Geo: fixes computation of geohash neighbours

The geohash grid it 8 cells wide and 4 cells tall. GeoHashUtils.neighbor(String,int,int.int) set the limit of the number of cells in y to < 3 rather than <= 3 resulting in it either not finding all neighbours or incorrectly searching for a neighbour in a different parent cell.

Closes #7226

src/main/java/org/elasticsearch/common/geo/GeoHashUtils.java

@@ -185,7 +185,7 @@ private final static String neighbor(String geohash, int level, int dx, int dy)
             // encode the cell directly. Otherwise find the cell next to this
             // cell recursively. Since encoding wraps around within a cell
             // it can be encoded here.
-            if (nx >= 0 && nx <= xLimit && ny >= 0 && ny < yLimit) {
+            if (nx >= 0 && nx <= xLimit && ny >= 0 && ny <= yLimit) {
                 return geohash.substring(0, level - 1) + encode(nx, ny);
             } else {
                 String neighbor = neighbor(geohash, level - 1, dx, dy);
@@ -511,5 +511,5 @@ private static double[] decodeCell(long geohash) {
             }
         }
         return interval;
-    }       
+    }
 }

src/test/java/org/elasticsearch/index/search/geo/GeoHashUtilsTests.java

@@ -24,7 +24,9 @@
 import org.elasticsearch.test.ElasticsearchTestCase;
 import org.junit.Test;
 
-import static org.junit.Assert.assertEquals;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
 
 /**
  *
@@ -86,4 +88,21 @@ public void testDecodeEncode() {
 
         assertEquals(geoHash, GeoHashUtils.encode(decode.lat(), decode.lon()));
     }
+
+    @Test
+    public void testNeighbours() {
+        String geohash = "gcpv";
+        List<String> expectedNeighbors = new ArrayList<>();
+        expectedNeighbors.add("gcpw");
+        expectedNeighbors.add("gcpy");
+        expectedNeighbors.add("u10n");
+        expectedNeighbors.add("gcpt");
+        expectedNeighbors.add("u10j");
+        expectedNeighbors.add("gcps");
+        expectedNeighbors.add("gcpu");
+        expectedNeighbors.add("u10h");
+        Collection<? super String> neighbors = new ArrayList<>();
+        GeoHashUtils.addNeighbors(geohash, neighbors );
+        assertEquals(expectedNeighbors, neighbors);
+    }
 }