Allow insertion of elements before and after a block, when the default block is not supported in the parent container

docs/reference-guides/data/data-core-block-editor.md

@@ -188,7 +188,8 @@ _Returns_
 
 ### getBlockHierarchyRootClientId
 
-Given a block client ID, returns the root of the hierarchy from which the block is nested, return the block itself for root level blocks.
+Given a block client ID, returns the root of the hierarchy from which the block is nested, return the block itself
+for root level blocks.
 
 _Parameters_
 

packages/block-editor/src/components/block-actions/index.js

@@ -30,8 +30,9 @@ export default function BlockActions( {
 		getBlocksByClientId,
 		canRemoveBlocks,
 		getTemplateLock,
+		__experimentalGetDefaultBlockForAllowedBlocks,
 	} = useSelect( ( select ) => select( blockEditorStore ), [] );
-	const { getDefaultBlockName, getGroupingBlockName } = useSelect(
+	const { getGroupingBlockName } = useSelect(
 		( select ) => select( blocksStore ),
 		[]
 	);
@@ -46,11 +47,11 @@ export default function BlockActions( {
 		);
 	} );
 
-	const canInsertDefaultBlock = canInsertBlockType(
-		getDefaultBlockName(),
+	const defaultBlock = __experimentalGetDefaultBlockForAllowedBlocks(
 		rootClientId
 	);
 
+	const canInsertDefaultBlock = !! defaultBlock;
 	const canRemove = canRemoveBlocks( clientIds, rootClientId );
 
 	const {

packages/block-editor/src/components/inner-blocks/index.js

@@ -52,6 +52,7 @@ function UncontrolledInnerBlocks( props ) {
 		orientation,
 		placeholder,
 		__experimentalLayout,
+		__experimentalDefaultBlock,
 	} = props;
 
 	useNestedSettingsUpdate(
@@ -60,7 +61,8 @@ function UncontrolledInnerBlocks( props ) {
 		templateLock,
 		captureToolbars,
 		orientation,
-		__experimentalLayout
+		__experimentalLayout,
+		__experimentalDefaultBlock
 	);
 
 	useInnerBlockTemplateSync(

packages/block-editor/src/components/inner-blocks/use-nested-settings-update.js

@@ -29,14 +29,19 @@ import { getLayoutType } from '../../layouts';
  * @param {string}   orientation     The direction in which the block
  *                                   should face.
  * @param {Object}   layout          The layout object for the block container.
+ *
+ * @param {[]}   __experimentalDefaultBlock     The default block: [ blockName, { blockAttributes } ].
+ *                                              Used to insert blocks of this type, before/after blocks
+ *                                              in inner blocks.
  */
 export default function useNestedSettingsUpdate(
 	clientId,
 	allowedBlocks,
 	templateLock,
 	captureToolbars,
 	orientation,
-	layout
+	layout,
+	__experimentalDefaultBlock
 ) {
 	const { updateBlockListSettings } = useDispatch( blockEditorStore );
 
@@ -64,6 +69,7 @@ export default function useNestedSettingsUpdate(
 	useLayoutEffect( () => {
 		const newSettings = {
 			allowedBlocks: _allowedBlocks,
+			__experimentalDefaultBlock,
 			templateLock:
 				templateLock === undefined ? parentLock : templateLock,
 		};

packages/block-editor/src/store/actions.js

@@ -12,7 +12,6 @@ import {
 	createBlock,
 	doBlocksMatchTemplate,
 	getBlockType,
-	getDefaultBlockName,
 	hasBlockSupport,
 	switchToBlockType,
 	synchronizeBlocksWithTemplate,
@@ -1131,16 +1130,33 @@ export function selectionChange(
  *
  * @return {Object} Action object
  */
-export function insertDefaultBlock( attributes, rootClientId, index ) {
+export function* insertDefaultBlock( attributes = {}, rootClientId, index ) {
+	// See if we specified a default for allowed blocks
+	const defaultBlock = yield controls.select(
+		blockEditorStoreName,
+		'__experimentalGetDefaultBlockForAllowedBlocks',
+		rootClientId
+	);
+
 	// Abort if there is no default block type (if it has been unregistered).
-	const defaultBlockName = getDefaultBlockName();
-	if ( ! defaultBlockName ) {
+	if ( ! defaultBlock ) {
 		return;
 	}
 
-	const block = createBlock( defaultBlockName, attributes );
+	const [ defaultBlockName, defaultBlockAttributes ] = defaultBlock;
+
+	// prefer the non-empty block attributes
+	let blockAttributes = attributes;
+	if (
+		Object.keys( attributes ).length === 0 &&
+		Object.keys( defaultBlockAttributes ).length > 0
+	) {
+		blockAttributes = defaultBlockAttributes;
+	}
+
+	const block = createBlock( defaultBlockName, blockAttributes );
 
-	return insertBlock( block, index, rootClientId );
+	return yield insertBlock( block, index, rootClientId );
 }
 
 /**

packages/block-editor/src/store/selectors.js

@@ -24,6 +24,7 @@ import createSelector from 'rememo';
 import {
 	getBlockType,
 	getBlockTypes,
+	getDefaultBlockName,
 	hasBlockSupport,
 	getPossibleBlockTransformations,
 	parse,
@@ -499,7 +500,8 @@ export const getBlockParentsByBlockName = createSelector(
 );
 
 /**
- * Given a block client ID, returns the root of the hierarchy from which the block is nested, return the block itself for root level blocks.
+ * Given a block client ID, returns the root of the hierarchy from which the block is nested, return the block itself
+ * for root level blocks.
  *
  * @param {Object} state    Editor state.
  * @param {string} clientId Block from which to find root client ID.
@@ -1991,6 +1993,32 @@ export function getBlockListSettings( state, clientId ) {
 	return state.blockListSettings[ clientId ];
 }
 
+/**
+ * Returns the default block name for a list of allowed blocks, if any exist.
+ *
+ * @param {Object}  state    Editor state.
+ * @param {?string} clientId Block client ID.
+ *
+ * @return {?[]}    default block, [ blockName, { blockAttributes } ].
+ */
+export function __experimentalGetDefaultBlockForAllowedBlocks(
+	state,
+	clientId
+) {
+	const settings = getBlockListSettings( state, clientId );
+
+	const [
+		blockName,
+		blockAttributes = {},
+	] = settings?.__experimentalDefaultBlock ?? [ getDefaultBlockName() ];
+
+	if ( ! canInsertBlockType( state, blockName, clientId ) ) {
+		return;
+	}
+
+	return [ blockName, blockAttributes ];
+}
+
 /**
  * Returns the editor settings.
  *

packages/block-editor/src/store/test/actions.js

@@ -31,6 +31,7 @@ const {
 	hideInsertionPoint,
 	insertBlock,
 	insertBlocks,
+	insertDefaultBlock,
 	mergeBlocks,
 	moveBlocksToPosition,
 	multiSelect,
@@ -459,6 +460,23 @@ describe( 'actions', () => {
 		} );
 	} );
 
+	describe( 'insertDefaultBlock', () => {
+		it( 'should check for allowed default block', () => {
+			const insertDefaultBlockGenerator = insertDefaultBlock(
+				{},
+				'testclientid',
+				0
+			);
+			expect( insertDefaultBlockGenerator.next().value ).toEqual(
+				controls.select(
+					blockEditorStoreName,
+					'__experimentalGetDefaultBlockForAllowedBlocks',
+					'testclientid'
+				)
+			);
+		} );
+	} );
+
 	describe( 'insertBlocks', () => {
 		it( 'should apply default styles to blocks if blocks do not contain a style', () => {
 			const ribsBlock = {