Datastream: _data_stream_timestamp use const variable to replace magic string (#81489)

A tiny change to improve _data_stream_timestamp.

test/framework/src/main/java/org/elasticsearch/cluster/metadata/DataStreamTestHelper.java

@@ -15,6 +15,7 @@ import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.Tuple;
 import org.elasticsearch.index.Index;
+import org.elasticsearch.index.mapper.DataStreamTimestampFieldMapper;
 import org.elasticsearch.test.ESTestCase;
 import org.hamcrest.Description;
 import org.hamcrest.Matcher;
@@ -113,7 +114,9 @@ public final class DataStreamTestHelper {
 
     public static String generateMapping(String timestampFieldName, String type) {
         return "{\n"
-            + "      \"_data_stream_timestamp\": {\n"
+            + "      \""
+            + DataStreamTimestampFieldMapper.NAME
+            + "\": {\n"
             + "        \"enabled\": true\n"
             + "      },"
             + "      \"properties\": {\n"

x-pack/plugin/data-streams/src/internalClusterTest/java/org/elasticsearch/datastreams/DataStreamIT.java

@@ -56,6 +56,7 @@ import org.elasticsearch.common.compress.CompressedXContent;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.index.IndexNotFoundException;
+import org.elasticsearch.index.mapper.DataStreamTimestampFieldMapper;
 import org.elasticsearch.index.mapper.DateFieldMapper;
 import org.elasticsearch.index.mapper.MapperParsingException;
 import org.elasticsearch.index.query.TermQueryBuilder;
@@ -1032,7 +1033,7 @@ public class DataStreamIT extends ESIntegTestCase {
         Map<?, ?> expectedMapping = Map.of(
             "properties",
             Map.of("@timestamp", Map.of("type", "date")),
-            "_data_stream_timestamp",
+            DataStreamTimestampFieldMapper.NAME,
             Map.of("enabled", true)
         );
         GetMappingsResponse getMappingsResponse = client().admin().indices().prepareGetMappings("logs-foobar").get();
@@ -1043,7 +1044,7 @@ public class DataStreamIT extends ESIntegTestCase {
         expectedMapping = Map.of(
             "properties",
             Map.of("@timestamp", Map.of("type", "date"), "my_field", Map.of("type", "keyword")),
-            "_data_stream_timestamp",
+            DataStreamTimestampFieldMapper.NAME,
             Map.of("enabled", true)
         );
         client().admin()

x-pack/plugin/data-streams/src/test/java/org/elasticsearch/xpack/datastreams/mapper/DataStreamTimestampFieldMapperTests.java

@@ -53,7 +53,7 @@ public class DataStreamTimestampFieldMapperTests extends MetadataMapperTestCase
     private XContentBuilder timestampMapping(boolean enabled, CheckedConsumer<XContentBuilder, IOException> propertiesBuilder)
         throws IOException {
         return topMapping(b -> {
-            b.startObject("_data_stream_timestamp").field("enabled", enabled).endObject();
+            b.startObject(DataStreamTimestampFieldMapper.NAME).field("enabled", enabled).endObject();
             b.startObject("properties");
             propertiesBuilder.accept(b);
             b.endObject();

x-pack/plugin/data-streams/src/test/java/org/elasticsearch/xpack/datastreams/mapper/MetadataCreateDataStreamServiceTests.java

@@ -11,6 +11,7 @@ import org.elasticsearch.Version;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.index.MapperTestUtils;
+import org.elasticsearch.index.mapper.DataStreamTimestampFieldMapper;
 import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.mapper.MappingLookup;
 import org.elasticsearch.indices.IndicesModule;
@@ -34,9 +35,11 @@ public class MetadataCreateDataStreamServiceTests extends ESTestCase {
 
     public void testValidateTimestampFieldMappingNoFieldMapping() {
         Exception e = expectThrows(IllegalStateException.class, () -> validateTimestampFieldMapping(createMappingLookup("{}")));
-        assertThat(e.getMessage(), equalTo("[_data_stream_timestamp] meta field has been disabled"));
+        assertThat(e.getMessage(), equalTo("[" + DataStreamTimestampFieldMapper.NAME + "] meta field has been disabled"));
         String mapping1 = "{\n"
-            + "      \"_data_stream_timestamp\": {\n"
+            + "      \""
+            + DataStreamTimestampFieldMapper.NAME
+            + "\": {\n"
             + "        \"enabled\": false\n"
             + "      },"
             + "      \"properties\": {\n"
@@ -46,7 +49,7 @@ public class MetadataCreateDataStreamServiceTests extends ESTestCase {
             + "      }\n"
             + "    }";
         e = expectThrows(IllegalStateException.class, () -> validateTimestampFieldMapping(createMappingLookup(mapping1)));
-        assertThat(e.getMessage(), equalTo("[_data_stream_timestamp] meta field has been disabled"));
+        assertThat(e.getMessage(), equalTo("[" + DataStreamTimestampFieldMapper.NAME + "] meta field has been disabled"));
 
         String mapping2 = generateMapping("@timestamp2", "date");
         e = expectThrows(IllegalArgumentException.class, () -> validateTimestampFieldMapping(createMappingLookup(mapping2)));