Ensure `index.mapping.single_type` can only be set on 5.x indices (#25375)

In 6.x we prevent multiple types and default to `index.mapping.single_type: false`
This change removes the registered setting and ensures that it's preserved for
5.x indices.

Relates to #24961

8 files changed, 114 insertions, 24 deletions

diff --git a/core/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java b/core/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java
index 890a43107c..1b57a2919f 100644
--- a/core/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java
+++ b/core/src/main/java/org/elasticsearch/common/settings/IndexScopedSettings.java
@@ -138,7 +138,6 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
         MapperService.INDEX_MAPPING_NESTED_FIELDS_LIMIT_SETTING,
         MapperService.INDEX_MAPPING_TOTAL_FIELDS_LIMIT_SETTING,
         MapperService.INDEX_MAPPING_DEPTH_LIMIT_SETTING,
-        MapperService.INDEX_MAPPING_SINGLE_TYPE_SETTING,
         BitsetFilterCache.INDEX_LOAD_RANDOM_ACCESS_FILTERS_EAGERLY_SETTING,
         IndexModule.INDEX_STORE_TYPE_SETTING,
         IndexModule.INDEX_STORE_PRE_LOAD_SETTING,
@@ -197,6 +196,9 @@ public final class IndexScopedSettings extends AbstractScopedSettings {
             case MergePolicyConfig.INDEX_MERGE_ENABLED:
             case IndexMetaData.INDEX_SHRINK_SOURCE_UUID_KEY:
             case IndexMetaData.INDEX_SHRINK_SOURCE_NAME_KEY:
+            case IndexSettings.INDEX_MAPPING_SINGLE_TYPE_SETTING_KEY:
+                // this was settable in 5.x but not anymore in 6.x so we have to preserve the value ie. make it read-only
+                // this can be removed in later versions
                 return true;
             default:
                 return IndexMetaData.INDEX_ROUTING_INITIAL_RECOVERY_GROUP_SETTING.getRawKey().match(key);
diff --git a/core/src/main/java/org/elasticsearch/index/IndexSettings.java b/core/src/main/java/org/elasticsearch/index/IndexSettings.java
index 537344ca65..fc2e476afc 100644
--- a/core/src/main/java/org/elasticsearch/index/IndexSettings.java
+++ b/core/src/main/java/org/elasticsearch/index/IndexSettings.java
@@ -169,6 +169,20 @@ public final class IndexSettings {
     public static final Setting<Integer> MAX_SLICES_PER_SCROLL = Setting.intSetting("index.max_slices_per_scroll",
         1024, 1, Property.Dynamic, Property.IndexScope);
 
+    public static final String INDEX_MAPPING_SINGLE_TYPE_SETTING_KEY = "index.mapping.single_type";
+    private static final Setting<Boolean> INDEX_MAPPING_SINGLE_TYPE_SETTING; // private - should not be registered
+    static {
+        Function<Settings, String> defValue = settings -> {
+            boolean singleType = true;
+            if (settings.getAsVersion(IndexMetaData.SETTING_VERSION_CREATED, null) != null) {
+                singleType = Version.indexCreated(settings).onOrAfter(Version.V_6_0_0_alpha1);
+            }
+            return Boolean.valueOf(singleType).toString();
+        };
+        INDEX_MAPPING_SINGLE_TYPE_SETTING = Setting.boolSetting(INDEX_MAPPING_SINGLE_TYPE_SETTING_KEY, defValue, Property.IndexScope,
+            Property.Final);
+    }
+
     private final Index index;
     private final Version version;
     private final Logger logger;
@@ -300,7 +314,11 @@ public final class IndexSettings {
         maxSlicesPerScroll = scopedSettings.get(MAX_SLICES_PER_SCROLL);
         this.mergePolicyConfig = new MergePolicyConfig(logger, this);
         this.indexSortConfig = new IndexSortConfig(this);
-        singleType = scopedSettings.get(MapperService.INDEX_MAPPING_SINGLE_TYPE_SETTING);
+        singleType = INDEX_MAPPING_SINGLE_TYPE_SETTING.get(indexMetaData.getSettings()); // get this from metadata - it's not registered
+        if ((singleType || version.before(Version.V_6_0_0_alpha1)) == false) {
+            throw new AssertionError(index.toString()  + "multiple types are only allowed on pre 6.x indices but version is: ["
+                + version + "]");
+        }
 
         scopedSettings.addSettingsUpdateConsumer(MergePolicyConfig.INDEX_COMPOUND_FORMAT_SETTING, mergePolicyConfig::setNoCFSRatio);
         scopedSettings.addSettingsUpdateConsumer(MergePolicyConfig.INDEX_MERGE_POLICY_EXPUNGE_DELETES_ALLOWED_SETTING, mergePolicyConfig::setExpungeDeletesAllowed);
diff --git a/core/src/main/java/org/elasticsearch/index/mapper/MapperService.java b/core/src/main/java/org/elasticsearch/index/mapper/MapperService.java
index 50f424c268..e279e12c40 100755
--- a/core/src/main/java/org/elasticsearch/index/mapper/MapperService.java
+++ b/core/src/main/java/org/elasticsearch/index/mapper/MapperService.java
@@ -97,17 +97,7 @@ public class MapperService extends AbstractIndexComponent implements Closeable {
     public static final boolean INDEX_MAPPER_DYNAMIC_DEFAULT = true;
     public static final Setting<Boolean> INDEX_MAPPER_DYNAMIC_SETTING =
         Setting.boolSetting("index.mapper.dynamic", INDEX_MAPPER_DYNAMIC_DEFAULT, Property.Dynamic, Property.IndexScope);
-    public static final Setting<Boolean> INDEX_MAPPING_SINGLE_TYPE_SETTING;
-    static {
-        Function<Settings, String> defValue = settings -> {
-            boolean singleType = true;
-            if (settings.getAsVersion(IndexMetaData.SETTING_VERSION_CREATED, null) != null) {
-                singleType = Version.indexCreated(settings).onOrAfter(Version.V_6_0_0_alpha1);
-            }
-            return Boolean.valueOf(singleType).toString();
-        };
-        INDEX_MAPPING_SINGLE_TYPE_SETTING = Setting.boolSetting("index.mapping.single_type", defValue, Property.IndexScope, Property.Final);
-    }
+
     private static ObjectHashSet<String> META_FIELDS = ObjectHashSet.from(
             "_uid", "_id", "_type", "_all", "_parent", "_routing", "_index",
             "_size", "_timestamp", "_ttl"
diff --git a/core/src/main/java/org/elasticsearch/index/mapper/TypeFieldMapper.java b/core/src/main/java/org/elasticsearch/index/mapper/TypeFieldMapper.java
index 2092e2521d..72c94edfd0 100644
--- a/core/src/main/java/org/elasticsearch/index/mapper/TypeFieldMapper.java
+++ b/core/src/main/java/org/elasticsearch/index/mapper/TypeFieldMapper.java
@@ -40,6 +40,7 @@ import org.elasticsearch.common.lucene.Lucene;
 import org.elasticsearch.common.lucene.search.Queries;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.index.fielddata.IndexFieldData;
 import org.elasticsearch.index.fielddata.plain.DocValuesIndexFieldData;
 import org.elasticsearch.index.fielddata.plain.ConstantIndexFieldData;
@@ -85,7 +86,7 @@ public class TypeFieldMapper extends MetadataFieldMapper {
 
         @Override
         public MetadataFieldMapper getDefault(MappedFieldType fieldType, ParserContext context) {
-            final Settings indexSettings = context.mapperService().getIndexSettings().getSettings();
+            final IndexSettings indexSettings = context.mapperService().getIndexSettings();
             return new TypeFieldMapper(indexSettings, fieldType);
         }
     }
@@ -263,18 +264,18 @@ public class TypeFieldMapper extends MetadataFieldMapper {
         }
     }
 
-    private TypeFieldMapper(Settings indexSettings, MappedFieldType existing) {
+    private TypeFieldMapper(IndexSettings indexSettings, MappedFieldType existing) {
         this(existing == null ? defaultFieldType(indexSettings) : existing.clone(),
              indexSettings);
     }
 
-    private TypeFieldMapper(MappedFieldType fieldType, Settings indexSettings) {
-        super(NAME, fieldType, defaultFieldType(indexSettings), indexSettings);
+    private TypeFieldMapper(MappedFieldType fieldType, IndexSettings indexSettings) {
+        super(NAME, fieldType, defaultFieldType(indexSettings), indexSettings.getSettings());
     }
 
-    private static MappedFieldType defaultFieldType(Settings indexSettings) {
+    private static MappedFieldType defaultFieldType(IndexSettings indexSettings) {
         MappedFieldType defaultFieldType = Defaults.FIELD_TYPE.clone();
-        if (MapperService.INDEX_MAPPING_SINGLE_TYPE_SETTING.get(indexSettings)) {
+        if (indexSettings.isSingleType()) {
             defaultFieldType.setIndexOptions(IndexOptions.NONE);
             defaultFieldType.setHasDocValues(false);
         } else {
diff --git a/core/src/test/java/org/elasticsearch/index/IndexSettingsTests.java b/core/src/test/java/org/elasticsearch/index/IndexSettingsTests.java
index bc3ee4b5f0..ad1c3f4143 100644
--- a/core/src/test/java/org/elasticsearch/index/IndexSettingsTests.java
+++ b/core/src/test/java/org/elasticsearch/index/IndexSettingsTests.java
@@ -288,7 +288,7 @@ public class IndexSettingsTests extends ESTestCase {
         settings = new IndexSettings(metaData, Settings.EMPTY);
         assertEquals(IndexSettings.MAX_RESULT_WINDOW_SETTING.get(Settings.EMPTY).intValue(), settings.getMaxResultWindow());
     }
-    
+
     public void testMaxAdjacencyMatrixFiltersSetting() {
         IndexMetaData metaData = newIndexMeta("index", Settings.builder()
             .put(IndexMetaData.SETTING_VERSION_CREATED, Version.CURRENT)
@@ -301,16 +301,16 @@ public class IndexSettingsTests extends ESTestCase {
             42).build()));
         assertEquals(42, settings.getMaxAdjacencyMatrixFilters());
         settings.updateIndexMetaData(newIndexMeta("index", Settings.EMPTY));
-        assertEquals(IndexSettings.MAX_ADJACENCY_MATRIX_FILTERS_SETTING.get(Settings.EMPTY).intValue(), 
+        assertEquals(IndexSettings.MAX_ADJACENCY_MATRIX_FILTERS_SETTING.get(Settings.EMPTY).intValue(),
                 settings.getMaxAdjacencyMatrixFilters());
 
         metaData = newIndexMeta("index", Settings.builder()
             .put(IndexMetaData.SETTING_VERSION_CREATED, Version.CURRENT)
             .build());
         settings = new IndexSettings(metaData, Settings.EMPTY);
-        assertEquals(IndexSettings.MAX_ADJACENCY_MATRIX_FILTERS_SETTING.get(Settings.EMPTY).intValue(), 
+        assertEquals(IndexSettings.MAX_ADJACENCY_MATRIX_FILTERS_SETTING.get(Settings.EMPTY).intValue(),
                 settings.getMaxAdjacencyMatrixFilters());
-    }    
+    }
 
     public void testGCDeletesSetting() {
         TimeValue gcDeleteSetting = new TimeValue(Math.abs(randomInt()), TimeUnit.MILLISECONDS);
@@ -435,4 +435,48 @@ public class IndexSettingsTests extends ESTestCase {
         assertEquals("2s", settings.get("index.refresh_interval"));
     }
 
+    public void testSingleTypeSetting() {
+        {
+            IndexSettings index = newIndexSettings(newIndexMeta("index", Settings.EMPTY), Settings.EMPTY);
+            IndexScopedSettings scopedSettings = index.getScopedSettings();
+            Settings build = Settings.builder().put(IndexSettings.INDEX_MAPPING_SINGLE_TYPE_SETTING_KEY, randomBoolean()).build();
+            scopedSettings.archiveUnknownOrInvalidSettings(build, e -> fail("unexpected unknown setting " + e),
+                (e, ex) -> fail("unexpected illegal setting"));
+            assertTrue(index.isSingleType());
+            expectThrows(IllegalArgumentException.class, () -> {
+                index.getScopedSettings()
+                    .validate(Settings.builder().put(IndexSettings.INDEX_MAPPING_SINGLE_TYPE_SETTING_KEY, randomBoolean()).build());
+            });
+        }
+        {
+            boolean single_type = randomBoolean();
+            Settings settings = Settings.builder().put(IndexMetaData.SETTING_VERSION_CREATED, Version.V_5_6_0)
+                .put(IndexMetaData.SETTING_NUMBER_OF_REPLICAS, 1)
+                .put(IndexMetaData.SETTING_NUMBER_OF_SHARDS, 1)
+                .put(IndexSettings.INDEX_MAPPING_SINGLE_TYPE_SETTING_KEY, single_type)
+                .build();
+            IndexMetaData meta = IndexMetaData.builder("index").settings(settings).build();
+            IndexSettings index = newIndexSettings(meta, Settings.EMPTY);
+            IndexScopedSettings scopedSettings = index.getScopedSettings();
+            Settings build = Settings.builder().put(IndexSettings.INDEX_MAPPING_SINGLE_TYPE_SETTING_KEY, randomBoolean()).build();
+            scopedSettings.archiveUnknownOrInvalidSettings(build, e -> fail("unexpected unknown setting " + e),
+                (e, ex) -> fail("unexpected illegal setting"));
+            assertEquals(single_type, index.isSingleType());
+        }
+
+        {
+            Settings settings = Settings.builder().put(IndexMetaData.SETTING_VERSION_CREATED, Version.CURRENT)
+                .put(IndexMetaData.SETTING_NUMBER_OF_REPLICAS, 1)
+                .put(IndexMetaData.SETTING_NUMBER_OF_SHARDS, 1)
+                .put(IndexSettings.INDEX_MAPPING_SINGLE_TYPE_SETTING_KEY, false)
+                .build();
+            IndexMetaData meta = IndexMetaData.builder("index").settings(settings).build();
+            try {
+                newIndexSettings(meta, Settings.EMPTY);
+                fail("should fail with assertion error");
+            } catch (AssertionError e) {
+                // all is well
+            }
+        }
+    }
 }
diff --git a/core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java b/core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java
index e9c8916634..8030c70a97 100644
--- a/core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java
+++ b/core/src/test/java/org/elasticsearch/index/engine/InternalEngineTests.java
@@ -1486,7 +1486,7 @@ public class InternalEngineTests extends ESTestCase {
             .put(IndexSettings.INDEX_GC_DELETES_SETTING.getKey(), "1h") // make sure this doesn't kick in on us
             .put(EngineConfig.INDEX_CODEC_SETTING.getKey(), codecName)
             .put(IndexMetaData.SETTING_VERSION_CREATED, Version.V_5_4_0)
-            .put(MapperService.INDEX_MAPPING_SINGLE_TYPE_SETTING.getKey(), true)
+            .put(IndexSettings.INDEX_MAPPING_SINGLE_TYPE_SETTING_KEY, true)
             .put(IndexSettings.MAX_REFRESH_LISTENERS_PER_SHARD.getKey(),
                 between(10, 10 * IndexSettings.MAX_REFRESH_LISTENERS_PER_SHARD.get(Settings.EMPTY)))
             .build());
diff --git a/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/old_cluster/10_basic.yml b/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/old_cluster/10_basic.yml
index 14c25aa101..e531216079 100644
--- a/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/old_cluster/10_basic.yml
+++ b/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/old_cluster/10_basic.yml
@@ -7,6 +7,28 @@
           settings:
             index:
               number_of_replicas: 0
+  - do:
+      indices.create:
+        index: multi_type_index
+        body:
+          settings:
+            index.number_of_replicas: 0
+            index.mapping.single_type: false
+
+  - do:
+      bulk:
+        refresh: true
+        body:
+          - '{"index": {"_index": "multi_type_index", "_type": "type1"}}'
+          - '{"f1": "v1_old", "f2": 0}'
+          - '{"index": {"_index": "multi_type_index", "_type": "type2"}}'
+          - '{"f1": "v1_old", "f2": 0}'
+
+  - do:
+      search:
+        index: multi_type_index
+
+  - match: { hits.total: 2 }
 
   - do:
       indices.create:
diff --git a/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/upgraded_cluster/10_basic.yml b/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/upgraded_cluster/10_basic.yml
index 96a3c4674c..b72b93ac32 100644
--- a/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/upgraded_cluster/10_basic.yml
+++ b/qa/rolling-upgrade/src/test/resources/rest-api-spec/test/upgraded_cluster/10_basic.yml
@@ -17,6 +17,19 @@
 
  - match: { hits.total: 5 } # just check we recovered fine
 
+
+ - do:
+    search:
+      index: multi_type_index
+
+ - match: { hits.total: 2 } # just check we recovered fine
+
+ - do:
+    indices.get_settings:
+      index: multi_type_index
+
+ - match: { multi_type_index.settings.index.mapping.single_type: "false"}
+
  - do:
      bulk:
         refresh: true