Issue #3285438: Prevent index clear when field mapping hasn't changed.

src/SearchAPI/BackendClient.php

@@ -269,7 +269,6 @@ class BackendClient implements BackendClientInterface {
    */
   public function updateIndex(IndexInterface $index): void {
     if ($this->indexExists($index)) {
-      $index->clear();
       $this->updateSettings($index);
       $this->updateFieldMapping($index);
     }
@@ -288,14 +287,58 @@ class BackendClient implements BackendClientInterface {
    *   Thrown when an underlying OpenSearch error occurs.
    */
   public function updateFieldMapping(IndexInterface $index): void {
-    $indexId = $this->getIndexId($index);
-    try {
-      $params = $this->fieldParamsBuilder->mapFieldParams($indexId, $index);
-      $this->client->indices()->putMapping($params);
+    if ($this->indexFieldsUpdated($index)) {
+      $indexId = $this->getIndexId($index);
+      try {
+        $params = $this->fieldParamsBuilder->mapFieldParams($indexId, $index);
+        $this->client->indices()->putMapping($params);
+        $index->reindex();
+      }
+      catch (OpenSearchException $e) {
+        throw new SearchApiException(sprintf('An error occurred updating field mappings for index %s.', $indexId), 0, $e);
+      }
     }
-    catch (OpenSearchException $e) {
-      throw new SearchApiException(sprintf('An error occurred updating field mappings for index %s.', $indexId), 0, $e);
+  }
+
+  /**
+   * Checks if the recently updated index had any fields changed.
+   *
+   * @param \Drupal\search_api\IndexInterface $index
+   *   The index that was just updated.
+   *
+   * @return bool
+   *   TRUE if any of the fields were updated, FALSE otherwise.
+   */
+  protected function indexFieldsUpdated(IndexInterface $index): bool {
+    if (!isset($index->original)) {
+      return TRUE;
+    }
+    /** @var \Drupal\search_api\IndexInterface $original */
+    $original = $index->original;
+
+    $old_fields = $original->getFields();
+    $new_fields = $index->getFields();
+    if (!$old_fields && !$new_fields) {
+      return FALSE;
+    }
+    if (array_diff_key($old_fields, $new_fields) || array_diff_key($new_fields, $old_fields)) {
+      return TRUE;
+    }
+
+    foreach ($new_fields as $field) {
+      if (!isset($old_fields[$field->getFieldIdentifier()])) {
+        continue;
+      }
+      $old_field = $old_fields[$field->getFieldIdentifier()];
+
+      if ($field->getSettings() != $old_field->getSettings()) {
+        return TRUE;
+      }
+      if ($field->getConfiguration() != $old_field->getConfiguration()) {
+        return TRUE;
+      }
     }
+    return FALSE;
   }
 
   /**