[8.x] Avoid serializing empty _source fields in mappings.

docs/changelog/122606.yaml

@@ -0,0 +1,5 @@
+pr: 122606
+summary: Avoid serializing empty `_source` fields in mappings
+area: Mapping
+type: bug
+issues: []

qa/full-cluster-restart/src/javaRestTest/java/org/elasticsearch/upgrades/FullClusterRestartDownsampleIT.java

@@ -11,6 +11,7 @@
 
 import com.carrotsearch.randomizedtesting.annotations.Name;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.client.Request;
 import org.elasticsearch.client.Response;
 import org.elasticsearch.common.Strings;
@@ -44,16 +45,26 @@ public class FullClusterRestartDownsampleIT extends ParameterizedFullClusterRest
 
     protected static LocalClusterConfigProvider clusterConfig = c -> {};
 
-    private static ElasticsearchCluster cluster = ElasticsearchCluster.local()
-        .distribution(DistributionType.DEFAULT)
-        .version(getOldClusterTestVersion())
-        .nodes(2)
-        .setting("xpack.security.enabled", "false")
-        .setting("indices.lifecycle.poll_interval", "5s")
-        .apply(() -> clusterConfig)
-        .feature(FeatureFlag.TIME_SERIES_MODE)
-        .feature(FeatureFlag.FAILURE_STORE_ENABLED)
-        .build();
+    private static ElasticsearchCluster cluster = buildCluster();
+
+    private static ElasticsearchCluster buildCluster() {
+        Version oldVersion = Version.fromString(OLD_CLUSTER_VERSION);
+        var cluster = ElasticsearchCluster.local()
+            .distribution(DistributionType.DEFAULT)
+            .version(getOldClusterTestVersion())
+            .nodes(2)
+            .setting("xpack.security.enabled", "false")
+            .setting("indices.lifecycle.poll_interval", "5s")
+            .apply(() -> clusterConfig)
+            .feature(FeatureFlag.TIME_SERIES_MODE)
+            .feature(FeatureFlag.FAILURE_STORE_ENABLED);
+
+        if (oldVersion.before(Version.fromString("8.19.0"))) {
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.DocumentMapper");
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.MapperService");
+        }
+        return cluster.build();
+    }
 
     @ClassRule
     public static TestRule ruleChain = RuleChain.outerRule(repoDirectory).around(cluster);

qa/full-cluster-restart/src/javaRestTest/java/org/elasticsearch/upgrades/FullClusterRestartIT.java

@@ -15,6 +15,7 @@
 
 import org.apache.http.util.EntityUtils;
 import org.elasticsearch.Build;
+import org.elasticsearch.Version;
 import org.elasticsearch.action.admin.cluster.settings.RestClusterGetSettingsResponse;
 import org.elasticsearch.client.Request;
 import org.elasticsearch.client.Response;
@@ -108,18 +109,28 @@ public class FullClusterRestartIT extends ParameterizedFullClusterRestartTestCas
 
     protected static LocalClusterConfigProvider clusterConfig = c -> {};
 
-    private static ElasticsearchCluster cluster = ElasticsearchCluster.local()
-        .distribution(DistributionType.DEFAULT)
-        .version(getOldClusterTestVersion())
-        .nodes(2)
-        .setting("path.repo", () -> repoDirectory.getRoot().getPath())
-        .setting("xpack.security.enabled", "false")
-        // some tests rely on the translog not being flushed
-        .setting("indices.memory.shard_inactive_time", "60m")
-        .apply(() -> clusterConfig)
-        .feature(FeatureFlag.TIME_SERIES_MODE)
-        .feature(FeatureFlag.FAILURE_STORE_ENABLED)
-        .build();
+    private static ElasticsearchCluster cluster = buildCluster();
+
+    private static ElasticsearchCluster buildCluster() {
+        Version oldVersion = Version.fromString(OLD_CLUSTER_VERSION);
+        var cluster = ElasticsearchCluster.local()
+            .distribution(DistributionType.DEFAULT)
+            .version(getOldClusterTestVersion())
+            .nodes(2)
+            .setting("path.repo", () -> repoDirectory.getRoot().getPath())
+            .setting("xpack.security.enabled", "false")
+            // some tests rely on the translog not being flushed
+            .setting("indices.memory.shard_inactive_time", "60m")
+            .apply(() -> clusterConfig)
+            .feature(FeatureFlag.TIME_SERIES_MODE)
+            .feature(FeatureFlag.FAILURE_STORE_ENABLED);
+
+        if (oldVersion.before(Version.fromString("8.19.0"))) {
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.DocumentMapper");
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.MapperService");
+        }
+        return cluster.build();
+    }
 
     @ClassRule
     public static TestRule ruleChain = RuleChain.outerRule(repoDirectory).around(cluster);

qa/full-cluster-restart/src/javaRestTest/java/org/elasticsearch/upgrades/LogsIndexModeFullClusterRestartIT.java

@@ -11,6 +11,7 @@
 
 import com.carrotsearch.randomizedtesting.annotations.Name;
 
+import org.elasticsearch.Version;
 import org.elasticsearch.client.Request;
 import org.elasticsearch.client.Response;
 import org.elasticsearch.client.RestClient;
@@ -33,17 +34,27 @@
 public class LogsIndexModeFullClusterRestartIT extends ParameterizedFullClusterRestartTestCase {
 
     @ClassRule
-    public static final ElasticsearchCluster cluster = ElasticsearchCluster.local()
-        .distribution(DistributionType.DEFAULT)
-        .version(getOldClusterTestVersion())
-        .module("constant-keyword")
-        .module("data-streams")
-        .module("mapper-extras")
-        .module("x-pack-aggregate-metric")
-        .module("x-pack-stack")
-        .setting("xpack.security.enabled", "false")
-        .setting("xpack.license.self_generated.type", "trial")
-        .build();
+    public static final ElasticsearchCluster cluster = buildCluster();
+
+    private static ElasticsearchCluster buildCluster() {
+        Version oldVersion = Version.fromString(OLD_CLUSTER_VERSION);
+        var cluster = ElasticsearchCluster.local()
+            .distribution(DistributionType.DEFAULT)
+            .version(getOldClusterTestVersion())
+            .module("constant-keyword")
+            .module("data-streams")
+            .module("mapper-extras")
+            .module("x-pack-aggregate-metric")
+            .module("x-pack-stack")
+            .setting("xpack.security.enabled", "false")
+            .setting("xpack.license.self_generated.type", "trial");
+
+        if (oldVersion.before(Version.fromString("8.19.0"))) {
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.DocumentMapper");
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.MapperService");
+        }
+        return cluster.build();
+    }
 
     public LogsIndexModeFullClusterRestartIT(@Name("cluster") FullClusterRestartUpgradeStatus upgradeStatus) {
         super(upgradeStatus);

qa/full-cluster-restart/src/javaRestTest/java/org/elasticsearch/upgrades/ParameterizedFullClusterRestartTestCase.java

@@ -38,7 +38,7 @@
 @TestCaseOrdering(FullClusterRestartTestOrdering.class)
 public abstract class ParameterizedFullClusterRestartTestCase extends ESRestTestCase {
     private static final Version MINIMUM_WIRE_COMPATIBLE_VERSION = Version.fromString("7.17.0");
-    private static final String OLD_CLUSTER_VERSION = System.getProperty("tests.old_cluster_version");
+    protected static final String OLD_CLUSTER_VERSION = System.getProperty("tests.old_cluster_version");
     private static IndexVersion oldIndexVersion;
     private static boolean upgradeFailed = false;
     private static boolean upgraded = false;

qa/mixed-cluster/build.gradle

@@ -85,6 +85,10 @@ buildParams.bwcVersions.withWireCompatible { bwcVersion, baseName ->
         setting 'health.master_history.no_master_transitions_threshold', '10'
       }
       requiresFeature 'es.index_mode_feature_flag_registered', Version.fromString("8.0.0")
+      if (bwcVersion.before(Version.fromString("8.19.0"))) {
+        jvmArgs '-da:org.elasticsearch.index.mapper.DocumentMapper'
+        jvmArgs '-da:org.elasticsearch.index.mapper.MapperService'
+      }
     }
 
     tasks.register("${baseName}#mixedClusterTest", StandaloneRestIntegTestTask) {

qa/rolling-upgrade/src/javaRestTest/java/org/elasticsearch/upgrades/AbstractRollingUpgradeTestCase.java

@@ -15,6 +15,7 @@
 import org.elasticsearch.test.cluster.ElasticsearchCluster;
 import org.elasticsearch.test.cluster.FeatureFlag;
 import org.elasticsearch.test.cluster.local.distribution.DistributionType;
+import org.elasticsearch.test.cluster.util.Version;
 import org.junit.ClassRule;
 import org.junit.rules.RuleChain;
 import org.junit.rules.TemporaryFolder;
@@ -26,20 +27,30 @@ public abstract class AbstractRollingUpgradeTestCase extends ParameterizedRollin
 
     private static final TemporaryFolder repoDirectory = new TemporaryFolder();
 
-    private static final ElasticsearchCluster cluster = ElasticsearchCluster.local()
-        .distribution(DistributionType.DEFAULT)
-        .version(getOldClusterTestVersion())
-        .nodes(NODE_NUM)
-        .setting("path.repo", new Supplier<>() {
-            @Override
-            @SuppressForbidden(reason = "TemporaryFolder only has io.File methods, not nio.File")
-            public String get() {
-                return repoDirectory.getRoot().getPath();
-            }
-        })
-        .setting("xpack.security.enabled", "false")
-        .feature(FeatureFlag.TIME_SERIES_MODE)
-        .build();
+    private static final ElasticsearchCluster cluster = buildCluster();
+
+    private static ElasticsearchCluster buildCluster() {
+        Version oldVersion = Version.fromString(OLD_CLUSTER_VERSION);
+        var cluster = ElasticsearchCluster.local()
+            .distribution(DistributionType.DEFAULT)
+            .version(getOldClusterTestVersion())
+            .nodes(NODE_NUM)
+            .setting("path.repo", new Supplier<>() {
+                @Override
+                @SuppressForbidden(reason = "TemporaryFolder only has io.File methods, not nio.File")
+                public String get() {
+                    return repoDirectory.getRoot().getPath();
+                }
+            })
+            .setting("xpack.security.enabled", "false")
+            .feature(FeatureFlag.TIME_SERIES_MODE);
+
+        if (oldVersion.before(Version.fromString("8.19.0"))) {
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.DocumentMapper");
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.MapperService");
+        }
+        return cluster.build();
+    }
 
     @ClassRule
     public static TestRule ruleChain = RuleChain.outerRule(repoDirectory).around(cluster);

qa/rolling-upgrade/src/javaRestTest/java/org/elasticsearch/upgrades/ParameterizedRollingUpgradeTestCase.java

@@ -36,7 +36,7 @@
 
 public abstract class ParameterizedRollingUpgradeTestCase extends ESRestTestCase {
     protected static final int NODE_NUM = 3;
-    private static final String OLD_CLUSTER_VERSION = System.getProperty("tests.old_cluster_version");
+    protected static final String OLD_CLUSTER_VERSION = System.getProperty("tests.old_cluster_version");
     private static final Set<Integer> upgradedNodes = new HashSet<>();
     private static TestFeatureService oldClusterTestFeatureService = null;
     private static boolean upgradeFailed = false;

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

@@ -172,14 +172,18 @@ public Builder(IndexMode indexMode, final Settings settings, boolean supportsChe
             this.supportsNonDefaultParameterValues = supportsCheckForNonDefaultParams == false
                 || settings.getAsBoolean(LOSSY_PARAMETERS_ALLOWED_SETTING_NAME, true);
             this.serializeMode = serializeMode;
-            this.mode = new Parameter<>(
-                "mode",
-                true,
-                () -> null,
-                (n, c, o) -> Mode.valueOf(o.toString().toUpperCase(Locale.ROOT)),
-                m -> toType(m).enabled.explicit() ? null : toType(m).mode,
+            this.mode = new Parameter<>("mode", true, () -> null, (n, c, o) -> Mode.valueOf(o.toString().toUpperCase(Locale.ROOT)), m -> {
+                var sfm = toType(m);
+                if (sfm.enabled.explicit()) {
+                    return null;
+                } else if (sfm.serializeMode) {
+                    return sfm.mode;
+                } else {
+                    return null;
+                }
+            },
                 (b, n, v) -> b.field(n, v.toString().toLowerCase(Locale.ROOT)),
-                v -> v.toString().toLowerCase(Locale.ROOT)
+                v -> v != null ? v.toString().toLowerCase(Locale.ROOT) : null
             ).setMergeValidator((previous, current, conflicts) -> (previous == current) || current != Mode.STORED)
                 // don't emit if `enabled` is configured
                 .setSerializerCheck((includeDefaults, isConfigured, value) -> serializeMode && value != null);
@@ -300,11 +304,20 @@ private static SourceFieldMapper resolveStaticInstance(final Mode sourceMode) {
         if (indexMode == IndexMode.STANDARD && settingSourceMode == Mode.STORED) {
             return DEFAULT;
         }
+        SourceFieldMapper sourceFieldMapper;
         if (c.indexVersionCreated().onOrAfter(IndexVersions.DEPRECATE_SOURCE_MODE_MAPPER)) {
-            return resolveStaticInstance(settingSourceMode);
+            sourceFieldMapper = resolveStaticInstance(settingSourceMode);
         } else {
-            return new SourceFieldMapper(settingSourceMode, Explicit.IMPLICIT_TRUE, Strings.EMPTY_ARRAY, Strings.EMPTY_ARRAY, true);
+            sourceFieldMapper = new SourceFieldMapper(
+                settingSourceMode,
+                Explicit.IMPLICIT_TRUE,
+                Strings.EMPTY_ARRAY,
+                Strings.EMPTY_ARRAY,
+                true
+            );
         }
+        indexMode.validateSourceFieldMapper(sourceFieldMapper);
+        return sourceFieldMapper;
     },
         c -> new Builder(
             c.getIndexSettings().getMode(),

server/src/test/java/org/elasticsearch/index/mapper/SourceFieldMapperTests.java

@@ -253,14 +253,14 @@ public void testSyntheticSourceInTimeSeries() throws IOException {
         });
         DocumentMapper mapper = createTimeSeriesModeDocumentMapper(mapping);
         assertTrue(mapper.sourceMapper().isSynthetic());
-        assertEquals("{\"_source\":{}}", mapper.sourceMapper().toString());
+        assertEquals("{}", mapper.sourceMapper().toString());
     }
 
     public void testSyntheticSourceWithLogsIndexMode() throws IOException {
         XContentBuilder mapping = fieldMapping(b -> { b.field("type", "keyword"); });
         DocumentMapper mapper = createLogsModeDocumentMapper(mapping);
         assertTrue(mapper.sourceMapper().isSynthetic());
-        assertEquals("{\"_source\":{}}", mapper.sourceMapper().toString());
+        assertEquals("{}", mapper.sourceMapper().toString());
     }
 
     public void testSupportsNonDefaultParameterValues() throws IOException {

x-pack/plugin/downsample/qa/mixed-cluster/src/yamlRestTest/java/org/elasticsearch/xpack/downsample/MixedClusterDownsampleRestIT.java

@@ -19,13 +19,23 @@
 public class MixedClusterDownsampleRestIT extends ESClientYamlSuiteTestCase {
 
     @ClassRule
-    public static ElasticsearchCluster cluster = ElasticsearchCluster.local()
-        .distribution(DistributionType.DEFAULT)
-        .withNode(node -> node.version(getOldVersion()))
-        .withNode(node -> node.version(Version.CURRENT))
-        .setting("xpack.security.enabled", "false")
-        .setting("xpack.license.self_generated.type", "trial")
-        .build();
+    public static ElasticsearchCluster cluster = buildCluster();
+
+    private static ElasticsearchCluster buildCluster() {
+        Version oldVersion = getOldVersion();
+        var cluster = ElasticsearchCluster.local()
+            .distribution(DistributionType.DEFAULT)
+            .withNode(node -> node.version(getOldVersion()))
+            .withNode(node -> node.version(Version.CURRENT))
+            .setting("xpack.security.enabled", "false")
+            .setting("xpack.license.self_generated.type", "trial");
+
+        if (oldVersion.before(Version.fromString("8.19.0"))) {
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.DocumentMapper");
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.MapperService");
+        }
+        return cluster.build();
+    }
 
     static Version getOldVersion() {
         return Version.fromString(System.getProperty("tests.old_cluster_version"));

x-pack/plugin/esql/qa/server/mixed-cluster/src/javaRestTest/java/org/elasticsearch/xpack/esql/qa/mixed/Clusters.java

@@ -25,6 +25,10 @@ public static ElasticsearchCluster mixedVersionCluster() {
         if (supportRetryOnShardFailures(oldVersion) == false) {
             cluster.setting("cluster.routing.rebalance.enable", "none");
         }
+        if (oldVersion.before(Version.fromString("8.19.0"))) {
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.DocumentMapper");
+            cluster.jvmArg("-da:org.elasticsearch.index.mapper.MapperService");
+        }
         return cluster.build();
     }
 

x-pack/plugin/logsdb/src/javaRestTest/java/org/elasticsearch/xpack/logsdb/LogsdbSnapshotRestoreIT.java

@@ -53,10 +53,6 @@ public class LogsdbSnapshotRestoreIT extends ESRestTestCase {
         .setting("cluster.logsdb.enabled", "true")
         .setting("xpack.security.enabled", "false")
         .setting("xpack.license.self_generated.type", "trial")
-        // TODO: remove when initializing / serializing default SourceFieldMapper instance have been fixed:
-        // (SFM's mode attribute often gets initialized, even when mode attribute isn't set)
-        .jvmArg("-da:org.elasticsearch.index.mapper.DocumentMapper")
-        .jvmArg("-da:org.elasticsearch.index.mapper.MapperService")
         .build();
 
     @ClassRule

x-pack/plugin/logsdb/src/yamlRestTest/resources/rest-api-spec/test/40_source_mode_setting.yml

@@ -754,7 +754,7 @@ modify logsdb index source mode to stored after index creation:
           _source:
             mode: stored
   - match: { error.type: "illegal_argument_exception" }
-  - match: { error.reason: "Mapper for [_source] conflicts with existing mapper:\n\tCannot update parameter [mode] from [synthetic] to [stored]" }
+  - match: { error.reason: "Mapper for [_source] conflicts with existing mapper:\n\tCannot update parameter [mode] from [null] to [stored]" }
 
 ---
 modify time_series index source mode to disabled after index creation:
@@ -812,4 +812,4 @@ modify time_series index source mode to stored after index creation:
           _source:
             mode: stored
   - match: { error.type: "illegal_argument_exception" }
-  - match: { error.reason: "Mapper for [_source] conflicts with existing mapper:\n\tCannot update parameter [mode] from [synthetic] to [stored]" }
+  - match: { error.reason: "Mapper for [_source] conflicts with existing mapper:\n\tCannot update parameter [mode] from [null] to [stored]" }

x-pack/qa/rolling-upgrade/build.gradle

@@ -60,6 +60,10 @@ buildParams.bwcVersions.withWireCompatible { bwcVersion, baseName ->
     setting 'xpack.security.transport.ssl.key', 'testnode.pem'
     setting 'xpack.security.transport.ssl.certificate', 'testnode.crt'
     keystore 'xpack.security.transport.ssl.secure_key_passphrase', 'testnode'
+    if (bwcVersion.before('8.19.0')) {
+      jvmArgs '-da:org.elasticsearch.index.mapper.MapperService'
+      jvmArgs '-da:org.elasticsearch.index.mapper.DocumentMapper'
+    }
 
     if (bwcVersion.onOrAfter('7.0.0')) {
       setting 'xpack.security.authc.realms.file.file1.order', '0'