Handle semantic text partial updates when the field is in an object

docs/changelog/117272.yaml

@@ -0,0 +1,5 @@
+pr: 117272
+summary: Handle semantic text partial updates when the field is in an object
+area: Relevance
+type: bug
+issues: []

server/src/main/java/org/elasticsearch/action/update/TransportUpdateAction.java

@@ -44,6 +44,7 @@
 import org.elasticsearch.index.IndexService;
 import org.elasticsearch.index.engine.VersionConflictEngineException;
 import org.elasticsearch.index.mapper.InferenceFieldMapper;
+import org.elasticsearch.index.mapper.InferenceFieldMapperUtil;
 import org.elasticsearch.index.mapper.Mapper;
 import org.elasticsearch.index.mapper.MappingLookup;
 import org.elasticsearch.index.shard.IndexShard;
@@ -412,7 +413,11 @@ private static UpdateHelper.Result deleteInferenceResults(
                         // This has two important side effects:
                         // - The inference field value will remain parsable by its mapper
                         // - The inference results will be removed, forcing them to be re-generated downstream
-                        updatedSource.put(inferenceFieldName, inferenceFieldMapper.getOriginalValue(updatedSource));
+                        InferenceFieldMapperUtil.insertValue(
+                            inferenceFieldName,
+                            updatedSource,
+                            inferenceFieldMapper.getOriginalValue(updatedSource)
+                        );
                         updatedSourceModified = true;
                         break;
                     }

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

@@ -0,0 +1,129 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+
+package org.elasticsearch.index.mapper;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+
+public class InferenceFieldMapperUtil {
+    private InferenceFieldMapperUtil() {}
+
+    /**
+     * <p>
+     * Insert or replace the path's value in the map with the provided new value. The map will be modified in-place.
+     * If the complete path does not exist in the map, it will be added to the deepest (sub-)map possible.
+     * </p>
+     * <p>
+     * For example, given the map:
+     * </p>
+     * <pre>
+     * {
+     *   "path1": {
+     *     "path2": {
+     *       "key1": "value1"
+     *     }
+     *   }
+     * }
+     * </pre>
+     * <p>
+     * And the caller wanted to insert {@code "path1.path2.path3.key2": "value2"}, the method would emit the modified map:
+     * </p>
+     * <pre>
+     * {
+     *   "path1": {
+     *     "path2": {
+     *       "key1": "value1",
+     *       "path3.key2": "value2"
+     *     }
+     *   }
+     * }
+     * </pre>
+     *
+     * @param path the value's path in the map.
+     * @param map the map to search and modify in-place.
+     * @param newValue the new value to assign to the path.
+     *
+     * @throws IllegalArgumentException If either the path cannot be fully traversed or there is ambiguity about where to insert the new
+     *                                  value.
+     */
+    public static void insertValue(String path, Map<?, ?> map, Object newValue) {
+        String[] pathElements = path.split("\\.");
+        if (pathElements.length == 0) {
+            return;
+        }
+
+        List<SuffixMap> suffixMaps = extractSuffixMaps(pathElements, 0, map);
+        if (suffixMaps.isEmpty()) {
+            // This should never happen. Throw in case it does for some reason.
+            throw new IllegalStateException("extractSuffixMaps returned an empty suffix map list");
+        } else if (suffixMaps.size() == 1) {
+            SuffixMap suffixMap = suffixMaps.getFirst();
+            suffixMap.map().put(suffixMap.suffix(), newValue);
+        } else {
+            throw new IllegalArgumentException(
+                "Path [" + path + "] could be inserted in " + suffixMaps.size() + " distinct ways, it is ambiguous which one to use"
+            );
+        }
+    }
+
+    private record SuffixMap(String suffix, Map<String, Object> map) {}
+
+    private static List<SuffixMap> extractSuffixMaps(String[] pathElements, int index, Object currentValue) {
+        if (currentValue instanceof List<?> valueList) {
+            List<SuffixMap> suffixMaps = new ArrayList<>(valueList.size());
+            for (Object o : valueList) {
+                suffixMaps.addAll(extractSuffixMaps(pathElements, index, o));
+            }
+
+            return suffixMaps;
+        } else if (currentValue instanceof Map<?, ?>) {
+            @SuppressWarnings("unchecked")
+            Map<String, Object> map = (Map<String, Object>) currentValue;
+            List<SuffixMap> suffixMaps = new ArrayList<>(map.size());
+
+            String key = pathElements[index];
+            while (index < pathElements.length) {
+                if (map.containsKey(key)) {
+                    if (index + 1 == pathElements.length) {
+                        // We found the complete path
+                        suffixMaps.add(new SuffixMap(key, map));
+                    } else {
+                        // We've matched that path partially, keep traversing to try to match it fully
+                        suffixMaps.addAll(extractSuffixMaps(pathElements, index + 1, map.get(key)));
+                    }
+                }
+
+                if (++index < pathElements.length) {
+                    key += "." + pathElements[index];
+                }
+            }
+
+            if (suffixMaps.isEmpty()) {
+                // We checked for all remaining elements in the path, and they do not exist. This means we found a leaf map that we should
+                // add the value to.
+                suffixMaps.add(new SuffixMap(key, map));
+            }
+
+            return suffixMaps;
+        } else {
+            throw new IllegalArgumentException(
+                "Path ["
+                    + String.join(".", Arrays.copyOfRange(pathElements, 0, index))
+                    + "] has value ["
+                    + currentValue
+                    + "] of type ["
+                    + currentValue.getClass().getSimpleName()
+                    + "], which cannot be traversed into further"
+            );
+        }
+    }
+}