Fix updating include_in_parent/include_in_root of nested field.

docs/reference/migration/migrate_7_8.asciidoc

@@ -41,6 +41,15 @@ Previously, Elasticsearch accepted mapping updates that tried to change the
 request didn't throw an error. As of 7.8, requests that attempt to change
 `enabled` on the root mapping will fail.
 
+[discrete]
+[[prevent-include-in-root-change]]
+==== `include_in_root` and `include_in_parent` cannot be changed
+
+Elasticsearch previously accepted mapping updates that changed the
+`include_in_root` and `include_in_parent` settings. The update was not
+applied, but the request didn't throw an error. As of 7.8, requests that
+attempt to change these settings will fail.
+
 [discrete]
 [[breaking_78_settings_changes]]
 === Settings changes

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

@@ -459,9 +459,7 @@ protected void doMerge(final ObjectMapper mergeWith) {
             this.dynamic = mergeWith.dynamic;
         }
 
-        if (isEnabled() != mergeWith.isEnabled()) {
-            throw new MapperException("The [enabled] parameter can't be updated for the object mapping [" + name() + "].");
-        }
+        checkObjectMapperParameters(mergeWith);
 
         for (Mapper mergeWithMapper : mergeWith) {
             Mapper mergeIntoMapper = mappers.get(mergeWithMapper.simpleName());
@@ -478,6 +476,22 @@ protected void doMerge(final ObjectMapper mergeWith) {
         }
     }
 
+    private void checkObjectMapperParameters(final ObjectMapper mergeWith) {
+        if (isEnabled() != mergeWith.isEnabled()) {
+            throw new MapperException("The [enabled] parameter can't be updated for the object mapping [" + name() + "].");
+        }
+
+        if (nested().isIncludeInParent() != mergeWith.nested().isIncludeInParent()) {
+            throw new MapperException("The [include_in_parent] parameter can't be updated for the nested object mapping [" +
+                name() + "].");
+        }
+
+        if (nested().isIncludeInRoot() != mergeWith.nested().isIncludeInRoot()) {
+            throw new MapperException("The [include_in_root] parameter can't be updated for the nested object mapping [" +
+                name() + "].");
+        }
+    }
+
     @Override
     public ObjectMapper updateFieldType(Map<String, MappedFieldType> fullNameToFieldType) {
         List<Mapper> updatedMappers = null;

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

@@ -19,7 +19,6 @@
 
 package org.elasticsearch.index.mapper;
 
-import java.util.HashSet;
 import org.apache.lucene.index.IndexableField;
 import org.elasticsearch.Version;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
@@ -41,6 +40,7 @@
 import java.io.UncheckedIOException;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.function.Function;
 
 import static org.elasticsearch.common.xcontent.XContentFactory.jsonBuilder;
@@ -749,4 +749,31 @@ public void testReorderParentBWC() throws IOException {
             }
         }
     }
+
+    public void testMergeNestedMappings() throws IOException {
+        MapperService mapperService = createIndex("index1", Settings.EMPTY, MapperService.SINGLE_MAPPING_NAME, jsonBuilder().startObject()
+            .startObject("properties")
+                .startObject("nested1")
+                    .field("type", "nested")
+                .endObject()
+            .endObject().endObject()).mapperService();
+
+        String mapping1 = Strings.toString(XContentFactory.jsonBuilder().startObject().startObject("type").startObject("properties")
+            .startObject("nested1").field("type", "nested").field("include_in_parent", true)
+            .endObject().endObject().endObject().endObject());
+
+        // cannot update `include_in_parent` dynamically
+        MapperException e1 = expectThrows(MapperException.class, () -> mapperService.merge("type",
+            new CompressedXContent(mapping1), MergeReason.MAPPING_UPDATE));
+        assertEquals("The [include_in_parent] parameter can't be updated for the nested object mapping [nested1].", e1.getMessage());
+
+        String mapping2 = Strings.toString(XContentFactory.jsonBuilder().startObject().startObject("type").startObject("properties")
+            .startObject("nested1").field("type", "nested").field("include_in_root", true)
+            .endObject().endObject().endObject().endObject());
+
+        // cannot update `include_in_root` dynamically
+        MapperException e2 = expectThrows(MapperException.class, () -> mapperService.merge("type",
+            new CompressedXContent(mapping2), MergeReason.MAPPING_UPDATE));
+        assertEquals("The [include_in_root] parameter can't be updated for the nested object mapping [nested1].", e2.getMessage());
+    }
 }