Aggregations: Fix geohash grid doc counts computation on multi-valued fields.

Close #8512

Author: jpountz

src/main/java/org/elasticsearch/search/aggregations/bucket/geogrid/GeoHashGridAggregator.java

@@ -74,14 +74,18 @@ public void collect(int doc, long owningBucketOrdinal) throws IOException {
         values.setDocument(doc);
         final int valuesCount = values.count();
 
+        long previous = Long.MAX_VALUE;
         for (int i = 0; i < valuesCount; ++i) {
             final long val = values.valueAt(i);
-            long bucketOrdinal = bucketOrds.add(val);
-            if (bucketOrdinal < 0) { // already seen
-                bucketOrdinal = - 1 - bucketOrdinal;
-                collectExistingBucket(doc, bucketOrdinal);
-            } else {
-                collectBucket(doc, bucketOrdinal);
+            if (previous != val || i == 0) {
+                long bucketOrdinal = bucketOrds.add(val);
+                if (bucketOrdinal < 0) { // already seen
+                    bucketOrdinal = - 1 - bucketOrdinal;
+                    collectExistingBucket(doc, bucketOrdinal);
+                } else {
+                    collectBucket(doc, bucketOrdinal);
+                }
+                previous = val;
             }
         }
     }

src/test/java/org/elasticsearch/search/aggregations/bucket/GeoHashGridTests.java

@@ -106,9 +106,7 @@ public void setupSuiteScopeCluster() throws Exception {
         for (int i = 0; i < numDocs; i++) {
             final int numPoints = random.nextInt(4);
             List<String> points = new ArrayList<>();
-            // TODO (#8512): this should be a Set, not a List. Currently if a document has two positions that have
-            // the same geo hash, it will increase the doc_count for this geo hash by 2 instead of 1
-            List<String> geoHashes = new ArrayList<>();
+            Set<String> geoHashes = new HashSet<>();
             for (int j = 0; j < numPoints; ++j) {
                 double lat = (180d * random.nextDouble()) - 90d;
                 double lng = (360d * random.nextDouble()) - 180d;