[UnifiedFieldList] Persist field list sections state in local storage

src/plugins/discover/public/application/main/components/sidebar/discover_sidebar.tsx

@@ -377,6 +377,7 @@ export function DiscoverSidebarComponent({
               {...fieldListGroupedProps}
               renderFieldItem={renderFieldItem}
               screenReaderDescriptionId={fieldSearchDescriptionId}
+              localStorageKeyPrefix="discover"
             />
           )}
         </EuiFlexItem>

src/plugins/unified_field_list/public/components/field_list_grouped/field_list_grouped.test.tsx

@@ -431,4 +431,54 @@ describe('UnifiedFieldList <FieldListGrouped /> + useGroupedFields()', () => {
       '2 selected fields. 10 popular fields. 25 available fields. 112 unmapped fields. 0 empty fields. 3 meta fields.'
     );
   });
+
+  it('persists sections state in local storage', async () => {
+    const wrapper = await mountGroupedList({
+      listProps: {
+        ...defaultProps,
+        fieldsExistenceStatus: ExistenceFetchStatus.succeeded,
+        localStorageKeyPrefix: 'test',
+      },
+      hookParams: {
+        dataViewId: dataView.id!,
+        allFields: manyFields,
+      },
+    });
+
+    // only Available is open
+    expect(
+      wrapper.find(FieldsAccordion).map((accordion) => accordion.prop('initialIsOpen'))
+    ).toStrictEqual([true, false, false, false]);
+
+    await act(async () => {
+      await wrapper
+        .find('[data-test-subj="fieldListGroupedEmptyFields"]')
+        .find('button')
+        .first()
+        .simulate('click');
+      await wrapper.update();
+    });
+
+    // now Empty is open too
+    expect(
+      wrapper.find(FieldsAccordion).map((accordion) => accordion.prop('initialIsOpen'))
+    ).toStrictEqual([true, false, true, false]);
+
+    const wrapper2 = await mountGroupedList({
+      listProps: {
+        ...defaultProps,
+        fieldsExistenceStatus: ExistenceFetchStatus.succeeded,
+        localStorageKeyPrefix: 'test',
+      },
+      hookParams: {
+        dataViewId: dataView.id!,
+        allFields: manyFields,
+      },
+    });
+
+    // both Available and Empty are open for the second instance
+    expect(
+      wrapper2.find(FieldsAccordion).map((accordion) => accordion.prop('initialIsOpen'))
+    ).toStrictEqual([true, false, true, false]);
+  });
 });

src/plugins/unified_field_list/public/components/field_list_grouped/field_list_grouped.tsx

@@ -8,6 +8,7 @@
 
 import { partition, throttle } from 'lodash';
 import React, { Fragment, useCallback, useEffect, useMemo, useState } from 'react';
+import useLocalStorage from 'react-use/lib/useLocalStorage';
 import { i18n } from '@kbn/i18n';
 import { EuiScreenReaderOnly, EuiSpacer } from '@elastic/eui';
 import { type DataViewField } from '@kbn/data-views-plugin/common';
@@ -18,10 +19,13 @@ import { ExistenceFetchStatus, FieldsGroup, FieldsGroupNames } from '../../types
 import './field_list_grouped.scss';
 
 const PAGINATION_SIZE = 50;
+export const LOCAL_STORAGE_KEY_SECTIONS = 'unifiedFieldList.initiallyOpenSections';
+
+type InitiallyOpenSections = Record<string, boolean>;
 
 function getDisplayedFieldsLength<T extends FieldListItem>(
   fieldGroups: FieldListGroups<T>,
-  accordionState: Partial<Record<string, boolean>>
+  accordionState: InitiallyOpenSections
 ) {
   return Object.entries(fieldGroups)
     .filter(([key]) => accordionState[key])
@@ -35,6 +39,7 @@ export interface FieldListGroupedProps<T extends FieldListItem> {
   renderFieldItem: FieldsAccordionProps<T>['renderFieldItem'];
   scrollToTopResetCounter: number;
   screenReaderDescriptionId?: string;
+  localStorageKeyPrefix?: string; // Your app name: "discover", "lens", etc. If not provided, sections state would not be persisted.
   'data-test-subj'?: string;
 }
 
@@ -45,6 +50,7 @@ function InnerFieldListGrouped<T extends FieldListItem = DataViewField>({
   renderFieldItem,
   scrollToTopResetCounter,
   screenReaderDescriptionId,
+  localStorageKeyPrefix,
   'data-test-subj': dataTestSubject = 'fieldListGrouped',
 }: FieldListGroupedProps<T>) {
   const hasSyncedExistingFields =
@@ -56,9 +62,22 @@ function InnerFieldListGrouped<T extends FieldListItem = DataViewField>({
   );
   const [pageSize, setPageSize] = useState(PAGINATION_SIZE);
   const [scrollContainer, setScrollContainer] = useState<Element | undefined>(undefined);
-  const [accordionState, setAccordionState] = useState<Partial<Record<string, boolean>>>(() =>
+  const [storedInitiallyOpenSections, storeInitiallyOpenSections] =
+    useLocalStorage<InitiallyOpenSections>(
+      `${localStorageKeyPrefix ? localStorageKeyPrefix + '.' : ''}${LOCAL_STORAGE_KEY_SECTIONS}`,
+      {}
+    );
+  const [accordionState, setAccordionState] = useState<InitiallyOpenSections>(() =>
     Object.fromEntries(
-      fieldGroupsToShow.map(([key, { isInitiallyOpen }]) => [key, isInitiallyOpen])
+      fieldGroupsToShow.map(([key, { isInitiallyOpen }]) => {
+        const storedInitiallyOpen = localStorageKeyPrefix
+          ? storedInitiallyOpenSections?.[key]
+          : null; // from localStorage
+        return [
+          key,
+          typeof storedInitiallyOpen === 'boolean' ? storedInitiallyOpen : isInitiallyOpen,
+        ];
+      })
     )
   );
 
@@ -256,6 +275,12 @@ function InnerFieldListGrouped<T extends FieldListItem = DataViewField>({
                       Math.min(Math.ceil(pageSize * 1.5), displayedFieldLength)
                     )
                   );
+                  if (localStorageKeyPrefix) {
+                    storeInitiallyOpenSections({
+                      ...storedInitiallyOpenSections,
+                      [key]: open,
+                    });
+                  }
                 }}
                 showExistenceFetchError={fieldsExistenceStatus === ExistenceFetchStatus.failed}
                 showExistenceFetchTimeout={fieldsExistenceStatus === ExistenceFetchStatus.failed} // TODO: deprecate timeout logic?

test/functional/apps/discover/group1/_sidebar.ts

@@ -45,6 +45,7 @@ export default function ({ getService, getPageObjects }: FtrProviderContext) {
       await kibanaServer.importExport.unload('test/functional/fixtures/kbn_archiver/discover');
       await kibanaServer.savedObjects.cleanStandardList();
       await kibanaServer.uiSettings.replace({});
+      await PageObjects.discover.cleanSidebarLocalStorage();
     });
 
     describe('field filtering', function () {

test/functional/page_objects/discover_page.ts

@@ -463,6 +463,10 @@ export class DiscoverPageObject extends FtrService {
     ).getAttribute('innerText');
   }
 
+  public async cleanSidebarLocalStorage(): Promise<void> {
+    await this.browser.setLocalStorageItem('discover.unifiedFieldList.initiallyOpenSections', '{}');
+  }
+
   public async waitUntilSidebarHasLoaded() {
     await this.retry.waitFor('sidebar is loaded', async () => {
       return (await this.getSidebarAriaDescription()).length > 0;

x-pack/plugins/lens/public/datasources/form_based/datapanel.test.tsx

@@ -374,6 +374,7 @@ describe('FormBased Data Panel', () => {
     (UseExistingFieldsApi.useExistingFieldsReader as jest.Mock).mockClear();
     (UseExistingFieldsApi.useExistingFieldsFetcher as jest.Mock).mockClear();
     UseExistingFieldsApi.resetExistingFieldsCache();
+    window.localStorage.removeItem('lens.unifiedFieldList.initiallyOpenSections');
   });
 
   it('should render a warning if there are no index patterns', async () => {

x-pack/plugins/lens/public/datasources/form_based/datapanel.tsx

@@ -428,6 +428,7 @@ export const InnerFormBasedDataPanel = function InnerFormBasedDataPanel({
           {...fieldListGroupedProps}
           renderFieldItem={renderFieldItem}
           data-test-subj="lnsIndexPattern"
+          localStorageKeyPrefix="lens"
         />
       </FieldList>
     </ChildDragDropProvider>

x-pack/plugins/lens/public/datasources/text_based/datapanel.tsx

@@ -161,6 +161,7 @@ export function TextBasedDataPanel({
             {...fieldListGroupedProps}
             renderFieldItem={renderFieldItem}
             data-test-subj="lnsTextBasedLanguages"
+            localStorageKeyPrefix="lens"
           />
         </FieldList>
       </ChildDragDropProvider>