Always return metadata version if metadata is requested (#37674)

If the indices of a ClusterStateRequest are specified, we fail to
include the cluster state metadata version in the response.

Relates  #37633

Author: dnhatn

server/src/main/java/org/elasticsearch/action/admin/cluster/state/TransportClusterStateAction.java

@@ -154,6 +154,7 @@ private void buildResponse(final ClusterStateRequest request,
 
         if (request.metaData()) {
             if (request.indices().length > 0) {
+                mdBuilder.version(currentState.metaData().version());
                 String[] indices = indexNameExpressionResolver.concreteIndexNames(currentState, request);
                 for (String filteredIndex : indices) {
                     IndexMetaData indexMetaData = currentState.metaData().index(filteredIndex);

server/src/test/java/org/elasticsearch/cluster/SimpleClusterStateIT.java

@@ -59,6 +59,7 @@
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertIndexTemplateExists;
 import static org.hamcrest.Matchers.equalTo;
+import static org.hamcrest.Matchers.greaterThan;
 import static org.hamcrest.Matchers.greaterThanOrEqualTo;
 import static org.hamcrest.Matchers.is;
 
@@ -111,6 +112,23 @@ public void testMetadata() throws Exception {
         assertThat(clusterStateResponse.getState().metaData().indices().size(), is(0));
     }
 
+    public void testMetadataVersion() {
+        createIndex("index-1");
+        createIndex("index-2");
+        long metadataVersion = client().admin().cluster().prepareState().get().getState().metaData().version();
+        assertThat(metadataVersion, greaterThan(0L));
+        assertThat(client().admin().cluster().prepareState().setIndices("index-1").get().getState().metaData().version(),
+            equalTo(metadataVersion));
+        assertThat(client().admin().cluster().prepareState().setIndices("index-2").get().getState().metaData().version(),
+            equalTo(metadataVersion));
+        assertThat(client().admin().cluster().prepareState().setIndices("*").get().getState().metaData().version(),
+            equalTo(metadataVersion));
+        assertThat(client().admin().cluster().prepareState().setIndices("not-found").get().getState().metaData().version(),
+            equalTo(metadataVersion));
+        assertThat(client().admin().cluster().prepareState().clear().setMetaData(false).get().getState().metaData().version(),
+            equalTo(0L));
+    }
+
     public void testIndexTemplates() throws Exception {
         client().admin().indices().preparePutTemplate("foo_template")
                 .setPatterns(Collections.singletonList("te*"))