Give precedence to index creation when mixing typed templates with typeless index creation and vice-versa. (#37871)

Currently if you mix typed templates and typeless index creation or typeless
templates and typed index creation then you will end up with an error because
Elasticsearch tries to create an index that has multiple types: `_doc` and
the explicit type name that you used.

This commit proposes to give precedence to the index creation call so that
the type from the template will be ignored if the index creation call is
typeless while the template is typed, and the type from the index creation
call will be used if there is a typeless template.

This is consistent with the fact that index creation already "wins" if a field
is defined differently in the index creation call and in a template: the
definition from the index creation call is used in such cases.

Closes #37773

docs/reference/mapping/removal_of_types.asciidoc

@@ -534,3 +534,77 @@ PUT index/_doc/1
 The <<docs-index_,GET>>, <<docs-delete,`DELETE`>>, <<docs-update,`_update`>> and <<search,`_search`>> APIs
 will continue to return a `_type` key in the response in 7.0, but it is considered deprecated and will be
 removed in 8.0.
+
+[float]
+=== Index templates
+
+It is recommended to make index templates typeless before upgrading to 7.0 by
+re-adding them with `include_type_name` set to `false`.
+
+In case typeless templates are used with typed index creation calls or typed
+templates are used with typeless index creation calls, the template will still
+be applied but the index creation call decides whether there should be a type
+or not. For instance in the below example, `index-1-01` will have a type in
+spite of the fact that it matches a template that is typeless, and `index-2-01`
+will be typeless in spite of the fact that it matches a template that defines
+a type. Both `index-1-01` and `index-2-01` will inherit the `foo` field from
+the template that they match.
+
+[source,js]
+--------------------------------------------------
+PUT _template/template1
+{
+  "index_patterns":[ "index-1-*" ],
+  "mappings": {
+    "properties": {
+      "foo": {
+        "type": "keyword"
+      }
+    }
+  }
+}
+
+PUT _template/template2?include_type_name=true
+{
+  "index_patterns":[ "index-2-*" ],
+  "mappings": {
+    "type": {
+      "properties": {
+        "foo": {
+          "type": "keyword"
+        }
+      }
+    }
+  }
+}
+
+PUT index-1-01?include_type_name=true
+{
+  "mappings": {
+    "type": {
+      "properties": {
+        "bar": {
+          "type": "long"
+        }
+      }
+    }
+  }
+}
+
+PUT index-2-01
+{
+  "mappings": {
+    "properties": {
+      "bar": {
+        "type": "long"
+      }
+    }
+  }
+}
+--------------------------------------------------
+// CONSOLE
+
+In case of implicit index creation, because of documents that get indexed in
+an index that doesn't exist yet, the template is always honored. This is
+usually not a problem due to the fact that typless index calls work on typed
+indices.

rest-api-spec/src/main/resources/rest-api-spec/test/indices.create/20_mix_typeless_typeful.yml

@@ -0,0 +1,137 @@
+---
+"Create a typeless index while there is a typed template":
+
+ - skip:
+      version: " - 6.99.99"
+      reason: needs change to be backported to 6.7
+
+ - do:
+      indices.put_template:
+          include_type_name: true
+          name: test_template
+          body:
+              index_patterns: test-*
+              mappings:
+                  my_type:
+                      properties:
+                          foo:
+                              type: keyword
+
+ - do:
+      indices.create:
+          include_type_name: false
+          index: test-1
+          body:
+              mappings:
+                  properties:
+                      bar:
+                          type: "long"
+
+ - do:
+      indices.get_mapping:
+          include_type_name: true
+          index: test-1
+
+ - is_true: test-1.mappings._doc # the index creation call won
+ - is_false: test-1.mappings.my_type
+ - is_true: test-1.mappings._doc.properties.foo
+ - is_true: test-1.mappings._doc.properties.bar
+
+---
+"Create a typed index while there is a typeless template":
+
+ - skip:
+      version: " - 6.99.99"
+      reason: needs change to be backported to 6.7
+
+ - do:
+      indices.put_template:
+          include_type_name: false
+          name: test_template
+          body:
+              index_patterns: test-*
+              mappings:
+                  properties:
+                      foo:
+                          type: keyword
+
+ - do:
+      indices.create: 
+          include_type_name: true
+          index: test-1
+          body:
+              mappings:
+                  my_type:
+                      properties:
+                          bar:
+                              type: "long"
+
+ - do:
+      indices.get_mapping:
+          include_type_name: true
+          index: test-1
+
+ - is_true: test-1.mappings.my_type # the index creation call won
+ - is_false: test-1.mappings._doc
+ - is_true: test-1.mappings.my_type.properties.foo
+ - is_true: test-1.mappings.my_type.properties.bar
+
+---
+"Implicitly create a typed index while there is a typeless template":
+
+ - skip:
+      version: " - 6.99.99"
+      reason: needs change to be backported to 6.7
+
+ - do:
+      indices.put_template:
+          include_type_name: false
+          name: test_template
+          body:
+              index_patterns: test-*
+              mappings:
+                  properties:
+                      foo:
+                          type: keyword
+
+ - do:
+      catch: /the final mapping would have more than 1 type/
+      index:
+          index: test-1
+          type: my_type
+          body: { bar: 42 }
+
+---
+"Implicitly create a typeless index while there is a typed template":
+
+ - skip:
+      version: " - 6.99.99"
+      reason: needs typeless index operations to work on typed indices
+
+ - do:
+      indices.put_template:
+          include_type_name: true
+          name: test_template
+          body:
+              index_patterns: test-*
+              mappings:
+                  my_type:
+                      properties:
+                          foo:
+                              type: keyword
+
+ - do:
+      index:
+          index: test-1
+          type: my_type
+          body: { bar: 42 }
+
+ - do:
+      indices.get_mapping:
+          include_type_name: true
+          index: test-1
+
+ - is_true: test-1.mappings.my_type # the template is honored
+ - is_false: test-1.mappings._doc
+ - is_true: test-1.mappings.my_type.properties.foo
+ - is_true: test-1.mappings.my_type.properties.bar

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

@@ -318,6 +318,28 @@ public class MetaDataCreateIndexService {
                             if (mappings.containsKey(cursor.key)) {
                                 XContentHelper.mergeDefaults(mappings.get(cursor.key),
                                     MapperService.parseMapping(xContentRegistry, mappingString));
+                            } else if (mappings.size() == 1 && cursor.key.equals(MapperService.SINGLE_MAPPING_NAME)) {
+                                // Typeless template with typed mapping
+                                Map<String, Object> templateMapping = MapperService.parseMapping(xContentRegistry, mappingString);
+                                assert templateMapping.size() == 1 : templateMapping;
+                                assert cursor.key.equals(templateMapping.keySet().iterator().next()) :
+                                    cursor.key + " != " + templateMapping;
+                                Map.Entry<String, Map<String, Object>> mappingEntry = mappings.entrySet().iterator().next();
+                                templateMapping = Collections.singletonMap(
+                                        mappingEntry.getKey(),                       // reuse type name from the mapping
+                                        templateMapping.values().iterator().next()); // but actual mappings from the template
+                                XContentHelper.mergeDefaults(mappingEntry.getValue(), templateMapping);
+                            } else if (template.mappings().size() == 1 && mappings.containsKey(MapperService.SINGLE_MAPPING_NAME)) {
+                                // Typed template with typeless mapping
+                                Map<String, Object> templateMapping = MapperService.parseMapping(xContentRegistry, mappingString);
+                                assert templateMapping.size() == 1 : templateMapping;
+                                assert cursor.key.equals(templateMapping.keySet().iterator().next()) :
+                                    cursor.key + " != " + templateMapping;
+                                Map<String, Object> mapping = mappings.get(MapperService.SINGLE_MAPPING_NAME);
+                                templateMapping = Collections.singletonMap(
+                                        MapperService.SINGLE_MAPPING_NAME,           // make template mapping typeless
+                                        templateMapping.values().iterator().next());
+                                XContentHelper.mergeDefaults(mapping, templateMapping);
                             } else {
                                 mappings.put(cursor.key,
                                     MapperService.parseMapping(xContentRegistry, mappingString));

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

@@ -310,6 +310,32 @@ public class IndexCreationTaskTests extends ESTestCase {
         assertThat(exception.getMessage(), startsWith("alias [alias1] has more than one write index ["));
     }
 
+    public void testTypelessTemplateWithTypedIndexCreation() throws Exception {
+        addMatchingTemplate(builder -> builder.putMapping("type", "{\"type\": {}}"));
+        setupRequestMapping(MapperService.SINGLE_MAPPING_NAME, new CompressedXContent("{\"_doc\":{}}"));
+        executeTask();
+        assertThat(getMappingsFromResponse(), Matchers.hasKey(MapperService.SINGLE_MAPPING_NAME));
+    }
+
+    public void testTypedTemplateWithTypelessIndexCreation() throws Exception {
+        addMatchingTemplate(builder -> builder.putMapping(MapperService.SINGLE_MAPPING_NAME, "{\"_doc\": {}}"));
+        setupRequestMapping("type", new CompressedXContent("{\"type\":{}}"));
+        executeTask();
+        assertThat(getMappingsFromResponse(), Matchers.hasKey("type"));
+    }
+
+    public void testTypedTemplate() throws Exception {
+        addMatchingTemplate(builder -> builder.putMapping("type", "{\"type\": {}}"));
+        executeTask();
+        assertThat(getMappingsFromResponse(), Matchers.hasKey("type"));
+    }
+
+    public void testTypelessTemplate() throws Exception {
+        addMatchingTemplate(builder -> builder.putMapping(MapperService.SINGLE_MAPPING_NAME, "{\"_doc\": {}}"));
+        executeTask();
+        assertThat(getMappingsFromResponse(), Matchers.hasKey(MapperService.SINGLE_MAPPING_NAME));
+    }
+
     private IndexRoutingTable createIndexRoutingTableWithStartedShards(Index index) {
         final IndexRoutingTable idxRoutingTable = mock(IndexRoutingTable.class);