[Search] Make Reference Field in Semantic_text Optional (#215562)

## Summary

This PR focus on making the `reference field` optional when adding
`semantic_text` field from Index Mapping. Previously, `semantic_text`
field was dependent on a text field and `copy_to` functionality which is
not required anymore.


https://github.com/user-attachments/assets/f19d0c1b-ac34-4f8d-b75d-993dd8720739


Added a label `optional` in the field after the video recording.
<img width="1227" alt="Screenshot 2025-03-26 at 1 25 22 PM"
src="https://github.com/user-attachments/assets/a11ed104-df50-47f4-a13f-9cf7187b2ad1"
/>


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.
- [X] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios
- [x] [Flaky Test
Runner](https://ci-stats.kibana.dev/trigger_flaky_test_runner/1) was
used on any tests changed

---------

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

x-pack/platform/plugins/private/translations/translations/fr-FR.json

@@ -21834,7 +21834,6 @@
     "xpack.idxMgmt.mappingsEditor.parameters.validations.pathIsRequiredErrorMessage": "Sélectionnez un champ vers lequel pointer l'alias.",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.positionIncrementGapIsRequiredErrorMessage": "Définir une valeur d'écart d'incrément de position",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.priorityIsRequiredErrorMessage": "Spécifiez une priorité.",
-    "xpack.idxMgmt.mappingsEditor.parameters.validations.referenceFieldIsRequiredErrorMessage": "Le champ de référence est obligatoire.",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.scalingFactorIsRequiredErrorMessage": "Facteur de montée en charge obligatoire.",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.smallerZeroErrorMessage": "La valeur doit être supérieure ou égale à 0.",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.spacesNotAllowedErrorMessage": "Les espaces ne sont pas autorisés.",

x-pack/platform/plugins/private/translations/translations/ja-JP.json

@@ -21813,7 +21813,6 @@
     "xpack.idxMgmt.mappingsEditor.parameters.validations.pathIsRequiredErrorMessage": "エイリアスが指し示すフィールドを選択します。",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.positionIncrementGapIsRequiredErrorMessage": "位置のインクリメントギャップ値の設定",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.priorityIsRequiredErrorMessage": "優先度を指定します。",
-    "xpack.idxMgmt.mappingsEditor.parameters.validations.referenceFieldIsRequiredErrorMessage": "参照フィールドは必須です。",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.scalingFactorIsRequiredErrorMessage": "スケーリングファクターが必要です。",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.smallerZeroErrorMessage": "値は0と同じかそれ以上でなければなりません。",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.spacesNotAllowedErrorMessage": "スペースは使用できません。",

x-pack/platform/plugins/private/translations/translations/zh-CN.json

@@ -21856,7 +21856,6 @@
     "xpack.idxMgmt.mappingsEditor.parameters.validations.pathIsRequiredErrorMessage": "选择将别名指向的字段。",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.positionIncrementGapIsRequiredErrorMessage": "设置位置递增间隔值",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.priorityIsRequiredErrorMessage": "指定优先级。",
-    "xpack.idxMgmt.mappingsEditor.parameters.validations.referenceFieldIsRequiredErrorMessage": "“参考字段”必填。",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.scalingFactorIsRequiredErrorMessage": "缩放因数必填。",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.smallerZeroErrorMessage": "值必须大于或等于 0。",
     "xpack.idxMgmt.mappingsEditor.parameters.validations.spacesNotAllowedErrorMessage": "不允许使用空格。",

x-pack/platform/plugins/shared/index_management/public/application/components/mappings_editor/__jest__/client_integration/helpers/mappings_editor.helpers.tsx

@@ -128,7 +128,12 @@ const createActions = (testBed: TestBed<TestSubjects>) => {
     return { field: find(testSubject as TestSubjects), testSubject };
   };
 
-  const addField = async (name: string, type: string, subType?: string) => {
+  const addField = async (
+    name: string,
+    type: string,
+    subType?: string,
+    referenceFieldValue?: string
+  ) => {
     await act(async () => {
       form.setInputValue('nameParameterInput', name);
       jest.advanceTimersByTime(0); // advance timers to allow the form to validate
@@ -151,6 +156,11 @@ const createActions = (testBed: TestBed<TestSubjects>) => {
       });
     }
 
+    if (referenceFieldValue !== undefined) {
+      form.setSelectValue('select', referenceFieldValue);
+      jest.advanceTimersByTime(0); // advance timers to allow the form to validate
+    }
+
     await act(async () => {
       find('createFieldForm.addButton').simulate('click');
       jest.advanceTimersByTime(0); // advance timers to allow the form to validate

x-pack/platform/plugins/shared/index_management/public/application/components/mappings_editor/__jest__/client_integration/mappings_editor.test.tsx

@@ -506,6 +506,44 @@ describe('Mappings editor: core', () => {
       const newField = { name: 'someNewField', type: 'semantic_text' };
       await addField(newField.name, newField.type);
 
+      updatedMappings = {
+        ...updatedMappings,
+        properties: {
+          ...updatedMappings.properties,
+          [newField.name]: { reference_field: '', type: 'semantic_text' },
+        },
+      };
+
+      ({ data } = await getMappingsEditorData(component));
+
+      expect(data).toEqual(updatedMappings);
+    });
+
+    test('updates mapping with reference field value for semantic_text field', async () => {
+      let updatedMappings = { ...defaultMappings };
+
+      const {
+        find,
+        actions: { addField },
+        component,
+      } = testBed;
+
+      /**
+       * Mapped fields
+       */
+      await act(async () => {
+        find('addFieldButton').simulate('click');
+        jest.advanceTimersByTime(0); // advance timers to allow the form to validate
+      });
+      component.update();
+
+      const newField = {
+        name: 'someNewField',
+        type: 'semantic_text',
+        referenceField: 'address.city',
+      };
+      await addField(newField.name, newField.type, undefined, newField.referenceField);
+
       updatedMappings = {
         ...updatedMappings,
         properties: {

x-pack/platform/plugins/shared/index_management/public/application/components/mappings_editor/components/document_fields/field_parameters/reference_field_selects.tsx

@@ -7,6 +7,8 @@
 
 import React from 'react';
 
+import { i18n } from '@kbn/i18n';
+import { EuiText } from '@elastic/eui';
 import { getFieldConfig } from '../../../lib';
 import { useMappingsState } from '../../../mappings_state_context';
 import { SuperSelectField, UseField } from '../../../shared_imports';
@@ -41,6 +43,16 @@ export const ReferenceFieldSelects = () => {
           euiFieldProps={{
             options: referenceFieldOptions,
           }}
+          labelAppend={
+            <EuiText size="xs" color="subdued">
+              {i18n.translate(
+                'xpack.idxMgmt.mappingsEditor.createField.referenceField.optionalLabel',
+                {
+                  defaultMessage: 'Optional',
+                }
+              )}
+            </EuiText>
+          }
           data-test-subj="referenceFieldSelect"
         />
       )}

x-pack/platform/plugins/shared/index_management/public/application/components/mappings_editor/components/document_fields/fields/create_field/create_field.tsx

@@ -127,15 +127,11 @@ export const CreateField = React.memo(function CreateFieldComponent({
       const defaultName = getFieldByPathName(allSemanticFields, 'semantic_text')
         ? ''
         : 'semantic_text';
-      const referenceField =
-        Object.values(allSemanticFields.byId)
-          .find((field) => field.source.type === 'text' && !field.isMultiField)
-          ?.path.join('.') || '';
       if (!form.getFormData().name) {
         form.setFieldValue('name', defaultName);
       }
       if (!form.getFormData().reference_field) {
-        form.setFieldValue('reference_field', referenceField);
+        form.setFieldValue('reference_field', '');
       }
     }
     // eslint-disable-next-line react-hooks/exhaustive-deps

x-pack/platform/plugins/shared/index_management/public/application/components/mappings_editor/constants/parameters_definition.tsx

@@ -1109,18 +1109,6 @@ export const PARAMETERS_DEFINITION: { [key in ParameterName]: ParameterDefinitio
       helpText: i18n.translate('xpack.idxMgmt.mappingsEditor.parameters.referenceFieldHelpText', {
         defaultMessage: 'Reference field for model inference.',
       }),
-      validations: [
-        {
-          validator: emptyField(
-            i18n.translate(
-              'xpack.idxMgmt.mappingsEditor.parameters.validations.referenceFieldIsRequiredErrorMessage',
-              {
-                defaultMessage: 'Reference field is required.',
-              }
-            )
-          ),
-        },
-      ],
     },
     schema: t.string,
   },

x-pack/platform/plugins/shared/index_management/public/application/components/mappings_editor/lib/utils.test.ts

@@ -462,8 +462,25 @@ describe('utils', () => {
         } as any;
         expect(getStateWithCopyToFields(state)).toEqual(state);
       });
-      test('returns state if semantic text field has no reference field', () => {
+      test('returns state if reference field in semantic_text is empty', () => {
         const state = {
+          fields: {
+            byId: {
+              '88ebcfdb-19b7-4458-9ea2-9488df54453d': {
+                id: '88ebcfdb-19b7-4458-9ea2-9488df54453d',
+                isMultiField: false,
+                source: {
+                  name: 'title',
+                  type: 'semantic_text',
+                  inference_id: 'id',
+                  reference_field: '',
+                },
+              },
+            },
+          },
+        } as any;
+
+        const expectedState = {
           fields: {
             byId: {
               '88ebcfdb-19b7-4458-9ea2-9488df54453d': {
@@ -478,7 +495,7 @@ describe('utils', () => {
             },
           },
         } as any;
-        expect(getStateWithCopyToFields(state)).toEqual(state);
+        expect(getStateWithCopyToFields(state)).toEqual(expectedState);
       });
       test('adds text field with copy to to state if semantic text field has reference field', () => {
         const state = {

x-pack/platform/plugins/shared/index_management/public/application/components/mappings_editor/lib/utils.ts

@@ -7,7 +7,7 @@
 
 import { v4 as uuidv4 } from 'uuid';
 
-import { cloneDeep } from 'lodash';
+import { cloneDeep, isEmpty } from 'lodash';
 import { InferenceServiceSettings } from '@elastic/elasticsearch/lib/api/types';
 import { LocalInferenceServiceSettings } from '@kbn/ml-trained-models-utils/src/constants/trained_models';
 import {
@@ -702,7 +702,7 @@ export function getStateWithCopyToFields(state: State): State {
   // Make sure we don't accidentally modify existing state
   let updatedState = cloneDeep(state);
   for (const field of Object.values(updatedState.fields.byId)) {
-    if (field.source.type === 'semantic_text' && field.source.reference_field) {
+    if (field.source.type === 'semantic_text') {
       // Check fields already added to the list of to-update fields first
       // API will not accept reference_field so removing it now
       const { reference_field: referenceField, ...source } = field.source;
@@ -711,6 +711,14 @@ export function getStateWithCopyToFields(state: State): State {
         throw new Error('Reference field is not a string');
       }
       field.source = source;
+
+      /* 
+        If no reference field is associated, 
+        no further processing is needed, so we can skip to the next one.
+      */
+      if (isEmpty(referenceField)) {
+        continue;
+      }
       const existingTextField =
         getFieldByPathName(updatedState.fields, referenceField) ||
         getFieldByPathName(updatedState.mappingViewFields || { byId: {} }, referenceField);