Warn about index.mapper.dynamic usage instead of erroring

When migrating from older versions of OpenSearch index.mapper.dynamic
could be present, use the deprecation system to warn about this state and
ignore this legacy setting so the index is usable.

Signed-off-by: Peter Nied <petern@amazon.com>

Author: peternied

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();