Two empty mappings now are created equally (elastic#107936)

* Two empty mappings reported equally in field_caps

* empty mapping now is {}

* iter

docs/changelog/107936.yaml

@@ -0,0 +1,6 @@
+pr: 107936
+summary: Two empty mappings now are created equally
+area: Mapping
+type: bug
+issues:
+ - 107031

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/indices.get_mapping/10_basic.yml

@@ -1,85 +1,85 @@
 ---
 setup:
   - do:
-        indices.create:
-          index: test_1
-          body:
-            mappings: {}
+      indices.create:
+        index: test_1
+        body:
+          mappings: {}
   - do:
-        indices.create:
-          index: test_2
-          body:
-            mappings: {}
+      indices.create:
+        index: test_2
+        body:
+          mappings: {}
 ---
 "Get /{index}/_mapping with empty mappings":
 
- - do:
-     indices.create:
-       index: t
+  - do:
+      indices.create:
+        index: t
 
- - do:
-     indices.get_mapping:
-       index: t
+  - do:
+      indices.get_mapping:
+        index: t
 
- - match: { t.mappings: {}}
+  - match: { t.mappings: {}}
 
 ---
 "Get /_mapping":
 
- - do:
-    indices.get_mapping: {}
+  - do:
+      indices.get_mapping: {}
 
- - is_true: test_1.mappings
- - is_true: test_2.mappings
+  - is_true: test_1.mappings
+  - is_true: test_2.mappings
 
 ---
 "Get /{index}/_mapping":
 
- - do:
-    indices.get_mapping:
-      index: test_1
+  - do:
+      indices.get_mapping:
+        index: test_1
 
- - is_true: test_1.mappings
- - is_false: test_2
+  - is_true: test_1.mappings
+  - is_false: test_2
 
 
 
 ---
 "Get /_all/_mapping":
 
- - do:
-    indices.get_mapping:
-      index: _all
+  - do:
+      indices.get_mapping:
+        index: _all
 
- - is_true: test_1.mappings
- - is_true: test_2.mappings
+  - is_true: test_1.mappings
+  - is_true: test_2.mappings
 
 ---
 "Get /*/_mapping":
 
- - do:
-    indices.get_mapping:
-      index: '*'
+  - do:
+      indices.get_mapping:
+        index: '*'
 
- - is_true: test_1.mappings
- - is_true: test_2.mappings
+  - is_true: test_1.mappings
+  - is_true: test_2.mappings
 
 ---
 "Get /index,index/_mapping":
 
- - do:
-    indices.get_mapping:
-      index: test_1,test_2
+  - do:
+      indices.get_mapping:
+        index: test_1,test_2
 
- - is_true: test_1.mappings
- - is_true: test_2.mappings
+  - is_true: test_1.mappings
+  - is_true: test_2.mappings
 
 ---
 "Get /index*/_mapping/":
 
- - do:
-    indices.get_mapping:
-      index: '*2'
+  - do:
+      indices.get_mapping:
+        index: '*2'
 
- - is_true: test_2.mappings
- - is_false: test_1
+  - is_true: test_2.mappings
+  - is_false: test_1

server/src/internalClusterTest/java/org/elasticsearch/action/admin/indices/create/CreateIndexIT.java

@@ -16,6 +16,8 @@
 import org.elasticsearch.action.admin.cluster.state.ClusterStateResponse;
 import org.elasticsearch.action.admin.indices.alias.Alias;
 import org.elasticsearch.action.admin.indices.mapping.get.GetMappingsResponse;
+import org.elasticsearch.action.fieldcaps.FieldCapabilitiesRequest;
+import org.elasticsearch.action.fieldcaps.FieldCapabilitiesResponse;
 import org.elasticsearch.action.support.ActionTestUtils;
 import org.elasticsearch.action.support.ActiveShardCount;
 import org.elasticsearch.action.support.IndicesOptions;
@@ -154,6 +156,20 @@ public void testEmptyMappings() throws Exception {
         assertTrue(mappings.sourceAsMap().isEmpty());
     }
 
+    public void testTwoEmptyEqualMappings() throws Exception {
+        assertAcked(prepareCreate("test1"));
+        assertAcked(prepareCreate("test2").setMapping(XContentFactory.jsonBuilder().startObject().endObject()));
+        FieldCapabilitiesRequest fieldCapsReq1 = new FieldCapabilitiesRequest();
+        fieldCapsReq1.indices("test1");
+        fieldCapsReq1.fields("*");
+        FieldCapabilitiesResponse fieldCapsResp1 = internalCluster().coordOnlyNodeClient().fieldCaps(fieldCapsReq1).actionGet();
+        FieldCapabilitiesRequest fieldCapsReq2 = new FieldCapabilitiesRequest();
+        fieldCapsReq2.indices("test2");
+        fieldCapsReq2.fields("*");
+        FieldCapabilitiesResponse fieldCapsResp2 = internalCluster().coordOnlyNodeClient().fieldCaps(fieldCapsReq2).actionGet();
+        assertEquals(fieldCapsResp1.get(), fieldCapsResp2.get());
+    }
+
     public void testInvalidShardCountSettings() throws Exception {
         int value = randomIntBetween(-10, 0);
         try {

server/src/main/java/org/elasticsearch/action/admin/indices/create/CreateIndexRequest.java

@@ -67,8 +67,9 @@ public class CreateIndexRequest extends AcknowledgedRequest<CreateIndexRequest>
     private boolean initializeFailureStore;
 
     private Settings settings = Settings.EMPTY;
+    public static final String EMPTY_MAPPINGS = "{}";
 
-    private String mappings = "{}";
+    private String mappings = EMPTY_MAPPINGS;
 
     private final Set<Alias> aliases = new HashSet<>();
 
@@ -284,8 +285,11 @@ private CreateIndexRequest mapping(BytesReference source, XContentType xContentT
     }
 
     private CreateIndexRequest mapping(String type, Map<String, ?> source) {
-        // wrap it in a type map if its not
-        if (source.size() != 1 || source.containsKey(type) == false) {
+        if (source.isEmpty()) {
+            // If no source is provided we return empty mappings
+            return mapping(EMPTY_MAPPINGS);
+        } else if (source.size() != 1 || source.containsKey(type) == false) {
+            // wrap it in a type map if its not
             source = Map.of(MapperService.SINGLE_MAPPING_NAME, source);
         } else if (MapperService.SINGLE_MAPPING_NAME.equals(type) == false) {
             // if it has a different type name, then unwrap and rewrap with _doc

server/src/main/java/org/elasticsearch/action/admin/indices/rollover/MetadataRolloverService.java

@@ -660,7 +660,7 @@ static void validate(
             }
             if ((request.settings().equals(Settings.EMPTY) == false)
                 || (request.aliases().size() > 0)
-                || (request.mappings().equals("{}") == false)) {
+                || (request.mappings().equals(CreateIndexRequest.EMPTY_MAPPINGS) == false)) {
                 throw new IllegalArgumentException(
                     "aliases, mappings, and index settings may not be specified when rolling over a data stream"
                 );

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

@@ -224,7 +224,7 @@ static void prepareBackingIndex(
         Settings nodeSettings
     ) throws IOException {
         MappingMetadata mm = im.mapping();
-        if (mm == null) {
+        if (mm == null || mm.equals(MappingMetadata.EMPTY_MAPPINGS)) {
             throw new IllegalArgumentException("backing index [" + im.getIndex().getName() + "] must have mappings for a timestamp field");
         }
 

x-pack/plugin/enrich/src/main/java/org/elasticsearch/xpack/enrich/EnrichPolicyRunner.java

@@ -172,7 +172,7 @@ private static List<Map<String, Object>> toMappings(GetIndexResponse response) {
     private Map<String, Object> getMappings(final GetIndexResponse getIndexResponse, final String sourceIndexName) {
         Map<String, MappingMetadata> mappings = getIndexResponse.mappings();
         MappingMetadata indexMapping = mappings.get(sourceIndexName);
-        if (indexMapping == MappingMetadata.EMPTY_MAPPINGS) {
+        if (MappingMetadata.EMPTY_MAPPINGS.equals(indexMapping)) {
             throw new ElasticsearchException(
                 "Enrich policy execution for [{}] failed. No mapping available on source [{}] included in [{}]",
                 policyName,