Fix navigation editor missing appender not showing appender when no blocks selected

packages/block-editor/src/components/inner-blocks/button-block-appender.js

@@ -1,3 +1,8 @@
+/**
+ * External dependencies
+ */
+import classnames from 'classnames';
+
 /**
  * Internal dependencies
  */
@@ -9,9 +14,13 @@ export const ButtonBlockAppender = ( {
 	showSeparator,
 	isFloating,
 	onAddBlock,
+	isToggle,
 } ) => {
 	return (
 		<BaseButtonBlockAppender
+			className={ classnames( {
+				'block-list-appender__toggle': isToggle,
+			} ) }
 			rootClientId={ clientId }
 			showSeparator={ showSeparator }
 			isFloating={ isFloating }

packages/block-library/src/navigation/edit.js

@@ -14,7 +14,6 @@ import {
 	Platform,
 } from '@wordpress/element';
 import {
-	InnerBlocks,
 	__experimentalUseInnerBlocksProps as useInnerBlocksProps,
 	InspectorControls,
 	JustifyToolbar,
@@ -100,10 +99,14 @@ function Navigation( {
 	setOverlayBackgroundColor,
 	overlayTextColor,
 	setOverlayTextColor,
+
+	// These props are used by the navigation editor to override specific
+	// navigation block settings.
 	hasSubmenuIndicatorSetting = true,
 	hasItemJustificationControls = true,
 	hasColorSettings = true,
 	customPlaceholder: CustomPlaceholder = null,
+	customAppender: CustomAppender = null,
 } ) {
 	const [ isPlaceholderShown, setIsPlaceholderShown ] = useState(
 		! hasExistingNavItems
@@ -145,19 +148,24 @@ function Navigation( {
 
 	const placeholder = useMemo( () => <PlaceholderPreview />, [] );
 
+	// When the block is selected itself or has a top level item selected that
+	// doesn't itself have children, show the standard appender. Else show no
+	// appender.
+	const appender =
+		isSelected ||
+		( isImmediateParentOfSelectedBlock && ! selectedBlockHasDescendants )
+			? undefined
+			: false;
+
 	const innerBlocksProps = useInnerBlocksProps(
 		{
 			className: 'wp-block-navigation__container',
 		},
 		{
 			allowedBlocks: ALLOWED_BLOCKS,
 			orientation: attributes.orientation,
-			renderAppender:
-				( isImmediateParentOfSelectedBlock &&
-					! selectedBlockHasDescendants ) ||
-				isSelected
-					? InnerBlocks.DefaultAppender
-					: false,
+			renderAppender: CustomAppender || appender,
+
 			// Ensure block toolbar is not too far removed from item
 			// being edited when in vertical mode.
 			// see: https://github.com/WordPress/gutenberg/pull/34615.

packages/e2e-tests/specs/experiments/navigation-editor.test.js

@@ -315,6 +315,22 @@ describe( 'Navigation editor', () => {
 		expect( await getSerializedBlocks() ).toMatchSnapshot();
 	} );
 
+	it( 'shows the trailing block appender within the navigation block when no blocks are selected', async () => {
+		await setUpResponseMocking( [
+			...getMenuMocks( { GET: assignMockMenuIds( menusFixture ) } ),
+			...getMenuItemMocks( { GET: menuItemsFixture } ),
+		] );
+		await visitNavigationEditor();
+
+		const selectedBlocks = await page.$$( '.wp-block.is-selected' );
+		expect( selectedBlocks.length ).toBe( 0 );
+
+		const blockListAppender = await page.$(
+			'.block-list-appender button[aria-label="Add block"]'
+		);
+		expect( blockListAppender ).toBeTruthy();
+	} );
+
 	it( 'shows a submenu when a link is selected and hides it when clicking the editor to deselect it', async () => {
 		await setUpResponseMocking( [
 			...getMenuMocks( { GET: assignMockMenuIds( menusFixture ) } ),

packages/edit-navigation/src/components/editor/style.scss

@@ -164,4 +164,12 @@
 			padding: 0;
 		}
 	}
+
+	// Override behavior that hides the navigation block's appender when it's deselected.
+	.block-editor-block-list__block:not(.is-selected):not(.has-child-selected):not(.block-editor-block-list__layout) {
+		.block-editor-block-list__layout > .block-list-appender .block-list-appender__toggle {
+			opacity: unset;
+			transform: unset;
+		}
+	}
 }

packages/edit-navigation/src/filters/add-navigation-editor-custom-appender.js

@@ -0,0 +1,76 @@
+/**
+ * WordPress dependencies
+ */
+import { useSelect } from '@wordpress/data';
+import { addFilter } from '@wordpress/hooks';
+import { createHigherOrderComponent } from '@wordpress/compose';
+import {
+	InnerBlocks,
+	store as blockEditorStore,
+} from '@wordpress/block-editor';
+
+function CustomAppender() {
+	return <InnerBlocks.ButtonBlockAppender isToggle />;
+}
+
+function EnhancedNavigationBlock( { blockEdit: BlockEdit, ...props } ) {
+	const clientId = props.clientId;
+	const {
+		noBlockSelected,
+		isSelected,
+		isImmediateParentOfSelectedBlock,
+		selectedBlockHasDescendants,
+	} = useSelect(
+		( select ) => {
+			const {
+				getClientIdsOfDescendants,
+				hasSelectedInnerBlock,
+				getSelectedBlockClientId,
+			} = select( blockEditorStore );
+			const _isImmediateParentOfSelectedBlock = hasSelectedInnerBlock(
+				clientId,
+				false
+			);
+			const selectedBlockId = getSelectedBlockClientId();
+			const _selectedBlockHasDescendants = !! getClientIdsOfDescendants( [
+				selectedBlockId,
+			] )?.length;
+
+			return {
+				isSelected: selectedBlockId === clientId,
+				noBlockSelected: ! selectedBlockId,
+				isImmediateParentOfSelectedBlock: _isImmediateParentOfSelectedBlock,
+				selectedBlockHasDescendants: _selectedBlockHasDescendants,
+			};
+		},
+		[ clientId ]
+	);
+
+	const customAppender =
+		noBlockSelected ||
+		isSelected ||
+		( isImmediateParentOfSelectedBlock && ! selectedBlockHasDescendants )
+			? CustomAppender
+			: false;
+
+	return <BlockEdit { ...props } customAppender={ customAppender } />;
+}
+
+const addNavigationEditorCustomAppender = createHigherOrderComponent(
+	( BlockEdit ) => ( props ) => {
+		if ( props.name !== 'core/navigation' ) {
+			return <BlockEdit { ...props } />;
+		}
+
+		// Use a separate component so that `useSelect` only run on the navigation block.
+		return <EnhancedNavigationBlock blockEdit={ BlockEdit } { ...props } />;
+	},
+	'withNavigationEditorCustomAppender'
+);
+
+export default () =>
+	addFilter(
+		'editor.BlockEdit',
+		'core/edit-navigation/with-navigation-editor-custom-appender',
+		addNavigationEditorCustomAppender
+	);

packages/edit-navigation/src/filters/add-navigation-editor-placeholder.js

@@ -1,11 +1,12 @@
 /**
  * WordPress dependencies
  */
+import { addFilter } from '@wordpress/hooks';
+import { createHigherOrderComponent } from '@wordpress/compose';
+
 /**
  * Internal dependencies
  */
-import { addFilter } from '@wordpress/hooks';
-import { createHigherOrderComponent } from '@wordpress/compose';
 import BlockPlaceholder from '../components/block-placeholder';
 
 const addNavigationEditorPlaceholder = createHigherOrderComponent(

packages/edit-navigation/src/filters/index.js

@@ -1,6 +1,7 @@
 /**
  * Internal dependencies
  */
+import addNavigationEditorCustomAppender from './add-navigation-editor-custom-appender';
 import addNavigationEditorPlaceholder from './add-navigation-editor-placeholder';
 import addMenuNameEditor from './add-menu-name-editor';
 import disableInsertingNonNavigationBlocks from './disable-inserting-non-navigation-blocks';
@@ -10,6 +11,7 @@ import removeSettingsUnsupportedFeatures from './remove-settings-unsupported-fea
 export const addFilters = (
 	shouldAddDisableInsertingNonNavigationBlocksFilter
 ) => {
+	addNavigationEditorCustomAppender();
 	addNavigationEditorPlaceholder();
 	addMenuNameEditor();
 	if ( shouldAddDisableInsertingNonNavigationBlocksFilter ) {