Fix constand_keyword test run and properly test recent behavior change (#117284)

Author: lkts

server/src/main/java/org/elasticsearch/index/mapper/MapperFeatures.java

@@ -57,6 +57,10 @@ public Set<NodeFeature> getFeatures() {
         );
     }
 
+    public static final NodeFeature CONSTANT_KEYWORD_SYNTHETIC_SOURCE_WRITE_FIX = new NodeFeature(
+        "mapper.constant_keyword.synthetic_source_write_fix"
+    );
+
     @Override
     public Set<NodeFeature> getTestFeatures() {
         return Set.of(
@@ -66,7 +70,8 @@ public Set<NodeFeature> getTestFeatures() {
             SourceFieldMapper.SOURCE_MODE_FROM_INDEX_SETTING,
             IgnoredSourceFieldMapper.IGNORED_SOURCE_AS_TOP_LEVEL_METADATA_ARRAY_FIELD,
             IgnoredSourceFieldMapper.ALWAYS_STORE_OBJECT_ARRAYS_IN_NESTED_OBJECTS,
-            MapperService.LOGSDB_DEFAULT_IGNORE_DYNAMIC_BEYOND_LIMIT
+            MapperService.LOGSDB_DEFAULT_IGNORE_DYNAMIC_BEYOND_LIMIT,
+            CONSTANT_KEYWORD_SYNTHETIC_SOURCE_WRITE_FIX
         );
     }
 }

x-pack/plugin/mapper-constant-keyword/build.gradle

@@ -6,7 +6,7 @@
  */
 
 apply plugin: 'elasticsearch.internal-es-plugin'
-apply plugin: 'elasticsearch.legacy-yaml-rest-test'
+apply plugin: 'elasticsearch.internal-yaml-rest-test'
 
 esplugin {
   name 'constant-keyword'

x-pack/plugin/mapper-constant-keyword/src/yamlRestTest/java/org/elasticsearch/xpack/constantkeyword/ConstantKeywordClientYamlTestSuiteIT.java

@@ -10,8 +10,10 @@
 import com.carrotsearch.randomizedtesting.annotations.Name;
 import com.carrotsearch.randomizedtesting.annotations.ParametersFactory;
 
+import org.elasticsearch.test.cluster.ElasticsearchCluster;
 import org.elasticsearch.test.rest.yaml.ClientYamlTestCandidate;
 import org.elasticsearch.test.rest.yaml.ESClientYamlSuiteTestCase;
+import org.junit.ClassRule;
 
 /** Runs yaml rest tests */
 public class ConstantKeywordClientYamlTestSuiteIT extends ESClientYamlSuiteTestCase {
@@ -24,4 +26,12 @@ public ConstantKeywordClientYamlTestSuiteIT(@Name("yaml") ClientYamlTestCandidat
     public static Iterable<Object[]> parameters() throws Exception {
         return ESClientYamlSuiteTestCase.createParameters();
     }
+
+    @ClassRule
+    public static ElasticsearchCluster cluster = ElasticsearchCluster.local().module("constant-keyword").build();
+
+    @Override
+    protected String getTestRestCluster() {
+        return cluster.getHttpAddresses();
+    }
 }

x-pack/plugin/mapper-constant-keyword/src/yamlRestTest/resources/rest-api-spec/test/20_synthetic_source.yml

@@ -1,7 +1,7 @@
 constant_keyword:
   - requires:
-      cluster_features: [ "mapper.source.mode_from_index_setting" ]
-      reason: "Source mode configured through index setting"
+      cluster_features: [ "mapper.constant_keyword.synthetic_source_write_fix" ]
+      reason: "Behavior fix"
 
   - do:
       indices.create:
@@ -26,13 +26,35 @@ constant_keyword:
         body:
           kwd: foo
 
+  - do:
+      index:
+        index:   test
+        id:      2
+        refresh: true
+        body:
+          kwd: foo
+          const_kwd: bar
+
   - do:
       search:
         index: test
         body:
           query:
             ids:
               values: [1]
+
+  - match:
+      hits.hits.0._source:
+        kwd: foo
+
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            ids:
+              values: [2]
+
   - match:
       hits.hits.0._source:
         kwd: foo