Emit a deprecation warning when a typed index template is triggered.

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

@@ -154,6 +154,11 @@ public ImmutableOpenMap<String, AliasMetaData> getAliases() {
         return this.aliases;
     }
 
+    public boolean isTypeless() {
+        return mappings.size() == 0 ||
+            (mappings.size()) == 1 && mappings.containsKey(MapperService.SINGLE_MAPPING_NAME);
+    }
+
     public static Builder builder(String name) {
         return new Builder(name);
     }

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

@@ -20,8 +20,8 @@
 package org.elasticsearch.cluster.metadata;
 
 import com.carrotsearch.hppc.cursors.ObjectObjectCursor;
-import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.apache.logging.log4j.message.ParameterizedMessage;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.ResourceAlreadyExistsException;
@@ -53,6 +53,7 @@
 import org.elasticsearch.common.ValidationException;
 import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.io.PathUtils;
+import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.common.settings.IndexScopedSettings;
 import org.elasticsearch.common.settings.Setting;
 import org.elasticsearch.common.settings.Settings;
@@ -100,6 +101,12 @@
  */
 public class MetaDataCreateIndexService {
     private static final Logger logger = LogManager.getLogger(MetaDataCreateIndexService.class);
+    private static final DeprecationLogger deprecationLogger = new DeprecationLogger(
+        LogManager.getLogger(MetaDataCreateIndexService.class));
+
+    static final String TYPES_DEPRECATION_MESSAGE = "[types removal] During index creation, an index " +
+        "template was triggered that contains a custom type. Index templates should no longer include a " +
+        "type name in the mappings, as types are deprecated and will be removed in the next major version.";
 
     public static final int MAX_INDEX_NAME_BYTES = 255;
 
@@ -312,6 +319,12 @@ public ClusterState execute(ClusterState currentState) throws Exception {
                 if (recoverFromIndex == null) {
                     // apply templates, merging the mappings into the request mapping if exists
                     for (IndexTemplateMetaData template : templates) {
+
+                        if (!template.isTypeless()) {
+                            deprecationLogger.deprecatedAndMaybeLog("trigger_template_with_types",
+                                TYPES_DEPRECATION_MESSAGE);
+                        }
+
                         templateNames.add(template.getName());
                         for (ObjectObjectCursor<String, CompressedXContent> cursor : template.mappings()) {
                             String mappingString = cursor.value.string();

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

@@ -65,6 +65,7 @@
 import java.util.function.Supplier;
 
 import static org.elasticsearch.cluster.metadata.IndexMetaData.SETTING_NUMBER_OF_SHARDS;
+import static org.elasticsearch.cluster.metadata.MetaDataCreateIndexService.TYPES_DEPRECATION_MESSAGE;
 import static org.elasticsearch.test.hamcrest.CollectionAssertions.hasAllKeys;
 import static org.elasticsearch.test.hamcrest.CollectionAssertions.hasKey;
 import static org.hamcrest.Matchers.containsString;
@@ -127,15 +128,15 @@ public void testMatchTemplates() throws Exception {
     public void testApplyDataFromTemplate() throws Exception {
         addMatchingTemplate(builder -> builder
                 .putAlias(AliasMetaData.builder("alias1"))
-                .putMapping("mapping1", createMapping())
+                .putMapping("_doc", createMapping())
                 .settings(Settings.builder().put("key1", "value1"))
         );
 
         final ClusterState result = executeTask();
 
         assertThat(result.metaData().index("test").getAliases(), hasKey("alias1"));
         assertThat(result.metaData().index("test").getSettings().get("key1"), equalTo("value1"));
-        assertThat(getMappingsFromResponse(), Matchers.hasKey("mapping1"));
+        assertThat(getMappingsFromResponse(), Matchers.hasKey("_doc"));
     }
 
     public void testApplyDataFromRequest() throws Exception {
@@ -162,7 +163,7 @@ public void testRequestDataHavePriorityOverTemplateData() throws Exception {
 
         addMatchingTemplate(builder -> builder
                     .putAlias(AliasMetaData.builder("alias1").searchRouting("fromTpl").build())
-                    .putMapping("mapping1", tplMapping)
+                    .putMapping("_doc", tplMapping)
                     .settings(Settings.builder().put("key1", "tplValue"))
         );
 
@@ -235,6 +236,17 @@ public void testTemplateOrder2() throws Exception {
         assertThat(result.metaData().index("test").getAliases().get("alias1").getSearchRouting(), equalTo("3"));
     }
 
+    public void testTypesDeprecation() throws Exception {
+        addMatchingTemplate(builder -> builder
+            .putMapping("custom_type", "{}")
+            .settings(Settings.builder().put(SETTING_NUMBER_OF_SHARDS, 10))
+        );
+
+        executeTask();
+        assertThat(getMappingsFromResponse(), Matchers.hasKey("custom_type"));
+        assertWarnings(TYPES_DEPRECATION_MESSAGE);
+    }
+
     public void testRequestStateOpen() throws Exception {
         when(request.state()).thenReturn(IndexMetaData.State.OPEN);