Warn about index.mapper.dynamic usage instead of erroring

CHANGELOG.md

@@ -126,6 +126,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Add a system property to configure YamlParser codepoint limits ([#12298](https://github.com/opensearch-project/OpenSearch/pull/12298))
 - Prevent read beyond slice boundary in ByteArrayIndexInput ([#10481](https://github.com/opensearch-project/OpenSearch/issues/10481))
 - Fix the "highlight.max_analyzer_offset" request parameter with "plain" highlighter ([#10919](https://github.com/opensearch-project/OpenSearch/pull/10919))
+- Warn about deprecated and ignored index.mapper.dynamic index setting ([#11193](https://github.com/opensearch-project/OpenSearch/pull/11193))
 
 ### Security
 

server/src/main/java/org/opensearch/index/mapper/MapperService.java

@@ -237,6 +237,7 @@ public MapperService(
         ScriptService scriptService
     ) {
         super(indexSettings);
+
         this.indexVersionCreated = indexSettings.getIndexVersionCreated();
         this.indexAnalyzers = indexAnalyzers;
         this.documentParser = new DocumentMapperParser(
@@ -261,7 +262,12 @@ public MapperService(
         this.idFieldDataEnabled = idFieldDataEnabled;
 
         if (INDEX_MAPPER_DYNAMIC_SETTING.exists(indexSettings.getSettings())) {
-            throw new IllegalArgumentException("Setting " + INDEX_MAPPER_DYNAMIC_SETTING.getKey() + " was removed after version 6.0.0");
+            deprecationLogger.deprecate(
+                index().getName() + INDEX_MAPPER_DYNAMIC_SETTING.getKey(),
+                "Index [{}] has setting [{}] that is not supported in OpenSearch, its value will be ignored.",
+                index().getName(),
+                INDEX_MAPPER_DYNAMIC_SETTING.getKey()
+            );
         }
     }
 

server/src/test/java/org/opensearch/index/mapper/MapperServiceTests.java

@@ -63,7 +63,9 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.List;
 import java.util.Map;
+import java.util.function.Function;
 
 import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.is;
@@ -541,6 +543,28 @@ public void testReloadSearchAnalyzers() throws IOException {
         );
     }
 
+    public void testMapperDynamicAllowedIgnored() {
+        final List<Function<Settings.Builder, Settings.Builder>> scenarios = List.of(
+            (builder) -> builder.putNull(MapperService.INDEX_MAPPER_DYNAMIC_SETTING.getKey()),
+            (builder) -> builder.put(MapperService.INDEX_MAPPER_DYNAMIC_SETTING.getKey(), true),
+            (builder) -> builder.put(MapperService.INDEX_MAPPER_DYNAMIC_SETTING.getKey(), false)
+        );
+
+        for (int i = 0; i < scenarios.size(); i++) {
+            final Settings.Builder defaultSettingsBuilder = Settings.builder()
+                .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
+                .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 1);
+
+            final Settings settings = scenarios.get(i).apply(defaultSettingsBuilder).build();
+
+            createIndex("test" + i, settings).mapperService();
+        }
+
+        assertWarnings(
+            "[index.mapper.dynamic] setting was deprecated in OpenSearch and will be removed in a future release! See the breaking changes documentation for the next major version."
+        );
+    }
+
     private boolean assertSameContainedFilters(TokenFilterFactory[] originalTokenFilter, NamedAnalyzer updatedAnalyzer) {
         ReloadableCustomAnalyzer updatedReloadableAnalyzer = (ReloadableCustomAnalyzer) updatedAnalyzer.analyzer();
         TokenFilterFactory[] newTokenFilters = updatedReloadableAnalyzer.getComponents().getTokenFilters();