Make legacy template noop updates not change cluster state (#64493)

When a legacy template does not change, there is no need to create and publish a new cluster state,
rather the update should be a noop.

Relates to #57851
Resolves #57662

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

@@ -169,7 +169,8 @@ public class IndexTemplateMetadata extends AbstractDiffable<IndexTemplateMetadat
         if (!settings.equals(that.settings)) return false;
         if (!patterns.equals(that.patterns)) return false;
 
-        return Objects.equals(version, that.version);
+        return Objects.equals(aliases, that.aliases) &&
+            Objects.equals(version, that.version);
     }
 
     @Override
@@ -180,6 +181,7 @@ public class IndexTemplateMetadata extends AbstractDiffable<IndexTemplateMetadat
         result = 31 * result + patterns.hashCode();
         result = 31 * result + settings.hashCode();
         result = 31 * result + mappings.hashCode();
+        result = 31 * result + aliases.hashCode();
         return result;
     }
 

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

@@ -805,6 +805,11 @@ public class MetadataIndexTemplateService {
             templateBuilder.putAlias(aliasMetadata);
         }
         IndexTemplateMetadata template = templateBuilder.build();
+        IndexTemplateMetadata existingTemplate = currentState.metadata().templates().get(request.name);
+        if (template.equals(existingTemplate)) {
+            // The template is unchanged, therefore there is no need for a cluster state update
+            return currentState;
+        }
 
         Metadata.Builder builder = Metadata.builder(currentState.metadata()).put(template);
 

server/src/test/java/org/elasticsearch/cluster/metadata/MetadataIndexTemplateServiceTests.java

@@ -98,6 +98,28 @@ public class MetadataIndexTemplateServiceTests extends ESSingleNodeTestCase {
         return List.of(DummyPlugin.class);
     }
 
+    public void testLegacyNoopUpdate() {
+        ClusterState state = ClusterState.EMPTY_STATE;
+        PutRequest pr = new PutRequest("api", "id");
+        pr.patterns(Arrays.asList("foo", "bar"));
+        if (randomBoolean()) {
+            pr.settings(Settings.builder()
+                .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 3).build());
+        }
+        if (randomBoolean()) {
+            pr.mappings("{}");
+        }
+        if (randomBoolean()) {
+            pr.aliases(Collections.singleton(new Alias("alias")));
+        }
+        pr.order(randomIntBetween(0, 10));
+        state = MetadataIndexTemplateService.innerPutTemplate(state, pr, new IndexTemplateMetadata.Builder("id"));
+
+        assertNotNull(state.metadata().templates().get("id"));
+
+        assertThat(MetadataIndexTemplateService.innerPutTemplate(state, pr, new IndexTemplateMetadata.Builder("id")), equalTo(state));
+    }
+
     public void testIndexTemplateInvalidNumberOfShards() {
         PutRequest request = new PutRequest("test", "test_shards");
         request.patterns(singletonList("test_shards*"));
@@ -727,7 +749,6 @@ public class MetadataIndexTemplateServiceTests extends ESSingleNodeTestCase {
         }
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/pull/57393")
     public void testResolveConflictingMappings() throws Exception {
         final MetadataIndexTemplateService service = getMetadataIndexTemplateService();
         ClusterState state = ClusterState.EMPTY_STATE;