Widget screens: set html block as freeform content handler (#33164)

packages/customize-widgets/src/index.js

@@ -11,6 +11,7 @@ import {
 	registerLegacyWidgetBlock,
 	registerLegacyWidgetVariations,
 } from '@wordpress/widgets';
+import { setFreeformContentHandlerName } from '@wordpress/blocks';
 
 /**
  * Internal dependencies
@@ -49,6 +50,12 @@ export function initialize( editorName, blockEditorSettings ) {
 	}
 	registerLegacyWidgetVariations( blockEditorSettings );
 
+	// As we are unregistering `core/freeform` to avoid the Classic block, we must
+	// replace it with something as the default freeform content handler. Failure to
+	// do this will result in errors in the default block parser.
+	// see: https://github.com/WordPress/gutenberg/issues/33097
+	setFreeformContentHandlerName( 'core/html' );
+
 	const SidebarControl = getSidebarControl( blockEditorSettings );
 
 	wp.customize.sectionConstructor.sidebar = getSidebarSection();

packages/edit-widgets/src/index.js

@@ -4,6 +4,7 @@
 import {
 	registerBlockType,
 	unstable__bootstrapServerSideBlockDefinitions, // eslint-disable-line camelcase
+	setFreeformContentHandlerName,
 } from '@wordpress/blocks';
 import { render } from '@wordpress/element';
 import {
@@ -63,6 +64,11 @@ export function initialize( id, settings ) {
 	settings.__experimentalFetchLinkSuggestions = ( search, searchOptions ) =>
 		fetchLinkSuggestions( search, searchOptions, settings );
 
+	// As we are unregistering `core/freeform` to avoid the Classic block, we must
+	// replace it with something as the default freeform content handler. Failure to
+	// do this will result in errors in the default block parser.
+	// see: https://github.com/WordPress/gutenberg/issues/33097
+	setFreeformContentHandlerName( 'core/html' );
 	render(
 		<Layout blockEditorSettings={ settings } />,
 		document.getElementById( id )