Button Block: Add parent-child syncing mechanism

extensions/blocks/button/attributes.js

@@ -15,6 +15,9 @@ export default {
 	uniqueId: {
 		type: 'string',
 	},
+	passthroughAttributes: {
+		type: 'object',
+	},
 	text: {
 		type: 'string',
 	},

extensions/blocks/button/edit.js

@@ -22,12 +22,14 @@ import applyFallbackStyles from './apply-fallback-styles';
 import ButtonBorderPanel from './button-border-panel';
 import ButtonColorsPanel from './button-colors-panel';
 import { IS_GRADIENT_AVAILABLE } from './constants';
+import usePassthroughAttributes from './use-passthrough-attributes';
 import './editor.scss';
 
 function ButtonEdit( {
 	attributes,
 	backgroundColor,
 	className,
+	clientId,
 	fallbackBackgroundColor,
 	fallbackTextColor,
 	setAttributes,
@@ -37,6 +39,8 @@ function ButtonEdit( {
 } ) {
 	const { borderRadius, element, placeholder, text } = attributes;
 
+	usePassthroughAttributes( { attributes, clientId, setAttributes } );
+
 	const onChange = value => {
 		// TODO: Remove `replace` once minimum Gutenberg version is 8.0 (to fully support `disableLineBreaks`)
 		const newValue = 'input' === element ? value.replace( /<br>/gim, ' ' ) : value;

extensions/blocks/button/use-passthrough-attributes.js

@@ -0,0 +1,40 @@
+/**
+ * External dependencies
+ */
+import { isEmpty, mapValues, pickBy } from 'lodash';
+
+/**
+ * WordPress dependencies
+ */
+import { useSelect } from '@wordpress/data';
+import { useEffect } from '@wordpress/element';
+
+export default function usePassthroughAttributes( { attributes, clientId, setAttributes } ) {
+	// `passthroughAttributes` is a map of child/parent attribute names,
+	// to indicate which parent attribute values will be injected into which child attributes.
+	// E.g. { childAttribute: 'parentAttribute' }
+	const { passthroughAttributes } = attributes;
+
+	const { attributesToSync } = useSelect( select => {
+		const { getBlockAttributes, getBlockHierarchyRootClientId } = select( 'core/block-editor' );
+		const parentAttributes = getBlockAttributes( getBlockHierarchyRootClientId( clientId ) );
+
+		// Here we actually map the parent attribute value to the child attribute.
+		// E.g. { childAttribute: 'foobar' }
+		const mappedAttributes = mapValues( passthroughAttributes, key => parentAttributes[ key ] );
+
+		// Discard all equals attributes
+		const validAttributes = pickBy(
+			mappedAttributes,
+			( value, key ) => value !== attributes[ key ]
+		);
+
+		return { attributesToSync: validAttributes };
+	} );
+
+	useEffect( () => {
+		if ( ! isEmpty( attributesToSync ) ) {
+			setAttributes( attributesToSync );
+		}
+	}, [ attributesToSync, setAttributes ] );
+}