[Mappings editor] Only add defined advanced options to request

src/plugins/es_ui_shared/static/forms/docs/core/use_form_hook.mdx

@@ -261,3 +261,48 @@ With this option you can decide if you want empty string value to be returned by
   "role": ""
 }
 ```
+
+#### stripUnsetFields
+
+**Type:** `boolean`
+**Default:** `false`
+
+Sometimes, we only want to include fields that have a defined initial value or if their value has been set by the user.
+In this case, set `stripUnsetFields` to `true`.
+
+Suppose we have a toggle field `autocompleteEnabled`, which doesn't have a specified default value passed to `useForm`:
+
+```js
+const { form } = useForm({
+  defaultValue: {
+    darkModeEnabled: false,
+    accessibilityEnabled: true,
+    autocompleteEnabled: undefined,
+  },
+  options: { stripUnsetFields: true },
+});
+```
+
+Initially, the form data includes only `darkModeEnabled` and `accessibilityEnabled` because `autocompleteEnabled` is stripped.
+
+```js
+{
+  "darkModeEnabled": false,
+  "accessibilityEnabled": true,
+}
+```
+
+Then the user toggles the `autocompleteEnabled` field to `false`. Now the field is included in the form data:
+
+```js
+{
+  "darkModeEnabled": false,
+  "accessibilityEnabled": true,
+  "autocompleteEnabled": false,
+}
+```
+
+Note: This option only considers the `defaultValue` config passed to `useForm()` to determine if the initial value is
+undefined. If a default value has been specified as a prop to the `<UseField />` component or in the form schema,
+but not in the `defaultValue` config for `useForm()`, the field would initially be populated with the specified default
+value, but it won't be included in the form data until the user explicitly sets its value.

src/plugins/es_ui_shared/static/forms/hook_form_lib/hooks/use_form.ts

@@ -25,6 +25,7 @@ import { createArrayItem, getInternalArrayFieldPath } from '../components/use_ar
 const DEFAULT_OPTIONS = {
   valueChangeDebounceTime: 500,
   stripEmptyFields: true,
+  stripUnsetFields: false,
 };
 
 export interface UseFormReturn<T extends FormData, I extends FormData> {
@@ -66,13 +67,18 @@ export function useForm<T extends FormData = FormData, I extends FormData = T>(
     return initDefaultValue(defaultValue);
   }, [defaultValue, initDefaultValue]);
 
-  const { valueChangeDebounceTime, stripEmptyFields: doStripEmptyFields } = options ?? {};
+  const {
+    valueChangeDebounceTime,
+    stripEmptyFields: doStripEmptyFields,
+    stripUnsetFields,
+  } = options ?? {};
   const formOptions = useMemo(
     () => ({
       stripEmptyFields: doStripEmptyFields ?? DEFAULT_OPTIONS.stripEmptyFields,
       valueChangeDebounceTime: valueChangeDebounceTime ?? DEFAULT_OPTIONS.valueChangeDebounceTime,
+      stripUnsetFields: stripUnsetFields ?? DEFAULT_OPTIONS.stripUnsetFields,
     }),
-    [valueChangeDebounceTime, doStripEmptyFields]
+    [valueChangeDebounceTime, doStripEmptyFields, stripUnsetFields]
   );
 
   const [isSubmitted, setIsSubmitted] = useState(false);
@@ -178,7 +184,10 @@ export function useForm<T extends FormData = FormData, I extends FormData = T>(
   const fieldsToArray = useCallback<() => FieldHook[]>(() => Object.values(fieldsRefs.current), []);
 
   const getFieldsForOutput = useCallback(
-    (fields: FieldsMap, opts: { stripEmptyFields: boolean }): FieldsMap => {
+    (
+      fields: FieldsMap,
+      opts: { stripEmptyFields: boolean; stripUnsetFields: boolean }
+    ): FieldsMap => {
       return Object.entries(fields).reduce((acc, [key, field]) => {
         if (!field.__isIncludedInOutput) {
           return acc;
@@ -191,11 +200,17 @@ export function useForm<T extends FormData = FormData, I extends FormData = T>(
           }
         }
 
+        if (opts.stripUnsetFields) {
+          if (!field.isDirty && getFieldDefaultValue(field.path) === undefined) {
+            return acc;
+          }
+        }
+
         acc[key] = field;
         return acc;
       }, {} as FieldsMap);
     },
-    []
+    [getFieldDefaultValue]
   );
 
   const updateFormDataAt: FormHook<T, I>['__updateFormDataAt'] = useCallback(
@@ -396,12 +411,13 @@ export function useForm<T extends FormData = FormData, I extends FormData = T>(
   const getFormData: FormHook<T, I>['getFormData'] = useCallback(() => {
     const fieldsToOutput = getFieldsForOutput(fieldsRefs.current, {
       stripEmptyFields: formOptions.stripEmptyFields,
+      stripUnsetFields: formOptions.stripUnsetFields,
     });
     const fieldsValue = mapFormFields(fieldsToOutput, (field) => field.__serializeValue());
     return serializer
       ? serializer(unflattenObject<I>(fieldsValue))
       : unflattenObject<T>(fieldsValue);
-  }, [getFieldsForOutput, formOptions.stripEmptyFields, serializer]);
+  }, [getFieldsForOutput, formOptions.stripEmptyFields, formOptions.stripUnsetFields, serializer]);
 
   const getErrors: FormHook<T, I>['getErrors'] = useCallback(() => {
     if (isValid === true) {

src/plugins/es_ui_shared/static/forms/hook_form_lib/types.ts

@@ -141,6 +141,10 @@ export interface FormOptions {
    * Remove empty string field ("") from form data
    */
   stripEmptyFields?: boolean;
+  /**
+   * Remove fields from form data that don't have initial value and are not modified by the user.
+   */
+  stripUnsetFields?: boolean;
 }
 
 export interface FieldHook<T = unknown, I = T> {

x-pack/plugins/index_management/public/application/components/mappings_editor/components/configuration_form/configuration_form.tsx

@@ -29,30 +29,19 @@ interface Props {
 }
 
 const formSerializer = (formData: GenericObject, sourceFieldMode?: string) => {
-  const {
-    dynamicMapping: {
-      enabled: dynamicMappingsEnabled,
-      throwErrorsForUnmappedFields,
-      /* eslint-disable @typescript-eslint/naming-convention */
-      numeric_detection,
-      date_detection,
-      dynamic_date_formats,
-      /* eslint-enable @typescript-eslint/naming-convention */
-    },
-    sourceField,
-    metaField,
-    _routing,
-    _size,
-    subobjects,
-  } = formData;
+  const { dynamicMapping, sourceField, metaField, _routing, _size, subobjects } = formData;
 
-  const dynamic = dynamicMappingsEnabled ? true : throwErrorsForUnmappedFields ? 'strict' : false;
+  const dynamic = dynamicMapping?.enabled
+    ? true
+    : dynamicMapping?.throwErrorsForUnmappedFields
+    ? 'strict'
+    : dynamicMapping?.enabled;
 
   const serialized = {
     dynamic,
-    numeric_detection,
-    date_detection,
-    dynamic_date_formats,
+    numeric_detection: dynamicMapping?.numeric_detection,
+    date_detection: dynamicMapping?.date_detection,
+    dynamic_date_formats: dynamicMapping?.dynamic_date_formats,
     _source: sourceFieldMode ? { mode: sourceFieldMode } : sourceField,
     _meta: metaField,
     _routing,
@@ -85,18 +74,18 @@ const formDeserializer = (formData: GenericObject) => {
 
   return {
     dynamicMapping: {
-      enabled: dynamic === true || dynamic === undefined,
-      throwErrorsForUnmappedFields: dynamic === 'strict',
+      enabled: dynamic === 'strict' ? false : dynamic,
+      throwErrorsForUnmappedFields: dynamic === 'strict' ? true : undefined,
       numeric_detection,
       date_detection,
       dynamic_date_formats,
     },
     sourceField: {
-      enabled: enabled === true || enabled === undefined,
+      enabled,
       includes,
       excludes,
     },
-    metaField: _meta ?? {},
+    metaField: _meta,
     _routing,
     _size,
     subobjects,
@@ -121,6 +110,7 @@ export const ConfigurationForm = React.memo(({ value, esNodesPlugins }: Props) =
     deserializer: formDeserializer,
     defaultValue: value,
     id: 'configurationForm',
+    options: { stripUnsetFields: true },
   });
   const dispatch = useDispatch();
   const { subscribe, submit, reset, getFormData } = form;

x-pack/test/functional/apps/index_management/index_template_wizard.ts

@@ -15,6 +15,7 @@ export default ({ getPageObjects, getService }: FtrProviderContext) => {
   const comboBox = getService('comboBox');
   const find = getService('find');
   const browser = getService('browser');
+  const log = getService('log');
 
   describe('Index template wizard', function () {
     before(async () => {
@@ -162,6 +163,40 @@ export default ({ getPageObjects, getService }: FtrProviderContext) => {
         expect(await testSubjects.exists('fieldSubType')).to.be(true);
         expect(await testSubjects.exists('nextButton')).to.be(true);
       });
+
+      it("advanced options tab doesn't add default values to request by default", async () => {
+        await pageObjects.indexManagement.changeMappingsEditorTab('advancedOptions');
+        await testSubjects.click('previewIndexTemplate');
+        const templatePreview = await testSubjects.getVisibleText('simulateTemplatePreview');
+
+        await log.debug(`Template preview text: ${templatePreview}`);
+
+        // All advanced options should not be part of the request
+        expect(templatePreview).to.not.contain('"dynamic"');
+        expect(templatePreview).to.not.contain('"subobjects"');
+        expect(templatePreview).to.not.contain('"dynamic_date_formats"');
+        expect(templatePreview).to.not.contain('"date_detection"');
+        expect(templatePreview).to.not.contain('"numeric_detection"');
+      });
+
+      it('advanced options tab adds the set values to the request', async () => {
+        await pageObjects.indexManagement.changeMappingsEditorTab('advancedOptions');
+
+        // Toggle the subobjects field to false
+        await testSubjects.click('subobjectsToggle');
+
+        await testSubjects.click('previewIndexTemplate');
+        const templatePreview = await testSubjects.getVisibleText('simulateTemplatePreview');
+
+        await log.debug(`Template preview text: ${templatePreview}`);
+
+        // Only the subobjects option should be part of the request
+        expect(templatePreview).to.contain('"subobjects": false');
+        expect(templatePreview).to.not.contain('"dynamic"');
+        expect(templatePreview).to.not.contain('"dynamic_date_formats"');
+        expect(templatePreview).to.not.contain('"date_detection"');
+        expect(templatePreview).to.not.contain('"numeric_detection"');
+      });
     });
   });
 };

x-pack/test/functional/page_objects/index_management_page.ts

@@ -118,6 +118,20 @@ export function IndexManagementPageProvider({ getService }: FtrProviderContext)
       await testSubjects.click(tab);
     },
 
+    async changeMappingsEditorTab(
+      tab: 'mappedFields' | 'runtimeFields' | 'dynamicTemplates' | 'advancedOptions'
+    ) {
+      const index = [
+        'mappedFields',
+        'runtimeFields',
+        'dynamicTemplates',
+        'advancedOptions',
+      ].indexOf(tab);
+
+      const tabs = await testSubjects.findAll('formTab');
+      await tabs[index].click();
+    },
+
     async clickNextButton() {
       await testSubjects.click('nextButton');
     },