Calculate routing num shards correctly during reshard

server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetadata.java

@@ -2001,12 +2001,8 @@ public Builder numberOfShards(int numberOfShards) {
          * The new shard count must be a multiple of the original shardcount.
          * We do not support shrinking the shard count.
          * @param shardCount   updated shardCount
-         *
-         * TODO: Check if this.version needs to be incremented
          */
-        public Builder reshardAddShards(int shardCount) {
-            // Assert routingNumShards is null ?
-            // Assert numberOfShards > 0
+        public Builder reshardAddShards(int shardCount, IndexMetadata sourceMetadata) {
             if (shardCount % numberOfShards() != 0) {
                 throw new IllegalArgumentException(
                     "New shard count ["
@@ -2019,13 +2015,12 @@ public Builder reshardAddShards(int shardCount) {
                         + "]"
                 );
             }
-            IndexVersion indexVersionCreated = indexCreatedVersion(settings);
             settings = Settings.builder().put(settings).put(SETTING_NUMBER_OF_SHARDS, shardCount).build();
             var newPrimaryTerms = new long[shardCount];
             Arrays.fill(newPrimaryTerms, this.primaryTerms.length, newPrimaryTerms.length, SequenceNumbers.UNASSIGNED_PRIMARY_TERM);
             System.arraycopy(primaryTerms, 0, newPrimaryTerms, 0, this.primaryTerms.length);
             primaryTerms = newPrimaryTerms;
-            routingNumShards = MetadataCreateIndexService.calculateNumRoutingShards(shardCount, indexVersionCreated);
+            routingNumShards = MetadataCreateIndexService.getIndexNumberOfRoutingShards(settings, sourceMetadata);
             return this;
         }