[8.x] Check index setting for source mode in SourceOnlySnapshotRepository (#116002)

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

@@ -242,7 +242,7 @@ public SourceFieldMapper build() {
         }
 
         private Mode resolveSourceMode() {
-            // If the `index.mapper.source.mode` exists it takes precedence to determine the source mode for `_source`
+            // If the `index.mapping.source.mode` exists it takes precedence to determine the source mode for `_source`
             // otherwise the mode is determined according to `_source.mode`.
             if (INDEX_MAPPER_SOURCE_MODE_SETTING.exists(settings)) {
                 return INDEX_MAPPER_SOURCE_MODE_SETTING.get(settings);
@@ -439,6 +439,10 @@ public static boolean isSynthetic(IndexSettings indexSettings) {
         return INDEX_MAPPER_SOURCE_MODE_SETTING.get(indexSettings.getSettings()) == SourceFieldMapper.Mode.SYNTHETIC;
     }
 
+    public static boolean isStored(IndexSettings indexSettings) {
+        return INDEX_MAPPER_SOURCE_MODE_SETTING.get(indexSettings.getSettings()) == Mode.STORED;
+    }
+
     public boolean isDisabled() {
         return mode == Mode.DISABLED;
     }

x-pack/plugin/core/src/main/java/org/elasticsearch/snapshots/sourceonly/SourceOnlySnapshotRepository.java

@@ -33,6 +33,7 @@
 import org.elasticsearch.index.engine.EngineFactory;
 import org.elasticsearch.index.engine.ReadOnlyEngine;
 import org.elasticsearch.index.mapper.MapperService;
+import org.elasticsearch.index.mapper.SourceFieldMapper;
 import org.elasticsearch.index.store.Store;
 import org.elasticsearch.index.translog.TranslogStats;
 import org.elasticsearch.repositories.FilterRepository;
@@ -139,8 +140,9 @@ private static Metadata metadataToSnapshot(Collection<IndexId> indices, Metadata
     @Override
     public void snapshotShard(SnapshotShardContext context) {
         final MapperService mapperService = context.mapperService();
-        if (mapperService.documentMapper() != null // if there is no mapping this is null
-            && mapperService.documentMapper().sourceMapper().isComplete() == false) {
+        if ((mapperService.documentMapper() != null // if there is no mapping this is null
+            && mapperService.documentMapper().sourceMapper().isComplete() == false)
+            || (mapperService.documentMapper() == null && SourceFieldMapper.isStored(mapperService.getIndexSettings()) == false)) {
             context.onFailure(
                 new IllegalStateException(
                     "Can't snapshot _source only on an index that has incomplete source ie. has _source disabled or filters the source"

x-pack/plugin/core/src/test/java/org/elasticsearch/snapshots/sourceonly/SourceOnlySnapshotShardTests.java

@@ -52,6 +52,7 @@
 import org.elasticsearch.index.engine.InternalEngineFactory;
 import org.elasticsearch.index.fieldvisitor.FieldsVisitor;
 import org.elasticsearch.index.mapper.SeqNoFieldMapper;
+import org.elasticsearch.index.mapper.SourceFieldMapper;
 import org.elasticsearch.index.mapper.SourceToParse;
 import org.elasticsearch.index.seqno.RetentionLeaseSyncer;
 import org.elasticsearch.index.seqno.SeqNoStats;
@@ -149,6 +150,55 @@ public void testSourceIncomplete() throws IOException {
         closeShards(shard);
     }
 
+    public void testSourceIncompleteSyntheticSourceNoDoc() throws IOException {
+        ShardRouting shardRouting = shardRoutingBuilder(
+            new ShardId("index", "_na_", 0),
+            randomAlphaOfLength(10),
+            true,
+            ShardRoutingState.INITIALIZING
+        ).withRecoverySource(RecoverySource.EmptyStoreRecoverySource.INSTANCE).build();
+        Settings settings = Settings.builder()
+            .put(IndexMetadata.SETTING_VERSION_CREATED, IndexVersion.current())
+            .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
+            .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+            .put(SourceFieldMapper.INDEX_MAPPER_SOURCE_MODE_SETTING.getKey(), "synthetic")
+            .build();
+        IndexMetadata metadata = IndexMetadata.builder(shardRouting.getIndexName()).settings(settings).primaryTerm(0, primaryTerm).build();
+        IndexShard shard = newShard(shardRouting, metadata, null, new InternalEngineFactory());
+        recoverShardFromStore(shard);
+        SnapshotId snapshotId = new SnapshotId("test", "test");
+        IndexId indexId = new IndexId(shard.shardId().getIndexName(), shard.shardId().getIndex().getUUID());
+        SourceOnlySnapshotRepository repository = new SourceOnlySnapshotRepository(createRepository());
+        repository.start();
+        try (Engine.IndexCommitRef snapshotRef = shard.acquireLastIndexCommit(true)) {
+            IndexShardSnapshotStatus indexShardSnapshotStatus = IndexShardSnapshotStatus.newInitializing(new ShardGeneration(-1L));
+            final PlainActionFuture<ShardSnapshotResult> future = new PlainActionFuture<>();
+            runAsSnapshot(
+                shard.getThreadPool(),
+                () -> repository.snapshotShard(
+                    new SnapshotShardContext(
+                        shard.store(),
+                        shard.mapperService(),
+                        snapshotId,
+                        indexId,
+                        new SnapshotIndexCommit(snapshotRef),
+                        null,
+                        indexShardSnapshotStatus,
+                        IndexVersion.current(),
+                        randomMillisUpToYear9999(),
+                        future
+                    )
+                )
+            );
+            IllegalStateException illegalStateException = expectThrows(IllegalStateException.class, future::actionGet);
+            assertEquals(
+                "Can't snapshot _source only on an index that has incomplete source ie. has _source disabled or filters the source",
+                illegalStateException.getMessage()
+            );
+        }
+        closeShards(shard);
+    }
+
     public void testIncrementalSnapshot() throws IOException {
         IndexShard shard = newStartedShard();
         for (int i = 0; i < 10; i++) {