Add block-based widgets editor

package.json

@@ -82,22 +82,24 @@
 		"@wordpress/api-fetch": "5.1.0",
 		"@wordpress/autop": "3.1.0",
 		"@wordpress/blob": "3.1.0",
-		"@wordpress/block-directory": "2.1.0",
+		"@wordpress/block-directory": "2.1.2",
 		"@wordpress/block-editor": "6.1.0",
-		"@wordpress/block-library": "3.1.0",
+		"@wordpress/block-library": "3.2.1",
 		"@wordpress/block-serialization-default-parser": "4.1.0",
 		"@wordpress/blocks": "9.1.0",
 		"@wordpress/components": "14.1.0",
 		"@wordpress/compose": "4.1.0",
-		"@wordpress/core-data": "3.1.0",
+		"@wordpress/core-data": "3.1.1",
+		"@wordpress/customize-widgets": "1.0.1",
 		"@wordpress/data": "5.1.0",
 		"@wordpress/data-controls": "2.1.0",
 		"@wordpress/date": "4.1.0",
 		"@wordpress/deprecated": "3.1.0",
 		"@wordpress/dom": "3.1.0",
 		"@wordpress/dom-ready": "3.1.0",
-		"@wordpress/edit-post": "4.1.0",
-		"@wordpress/editor": "10.1.0",
+		"@wordpress/edit-post": "4.1.2",
+		"@wordpress/edit-widgets": "2.1.2",
+		"@wordpress/editor": "10.1.1",
 		"@wordpress/element": "3.1.0",
 		"@wordpress/escape-html": "2.1.0",
 		"@wordpress/format-library": "2.1.0",
@@ -117,14 +119,15 @@
 		"@wordpress/primitives": "2.1.0",
 		"@wordpress/priority-queue": "2.1.0",
 		"@wordpress/redux-routine": "4.1.0",
-		"@wordpress/reusable-blocks": "2.1.0",
+		"@wordpress/reusable-blocks": "2.1.1",
 		"@wordpress/rich-text": "4.1.0",
 		"@wordpress/server-side-render": "2.1.0",
 		"@wordpress/shortcode": "3.1.0",
 		"@wordpress/token-list": "2.1.0",
 		"@wordpress/url": "3.1.0",
 		"@wordpress/viewport": "3.1.0",
 		"@wordpress/warning": "2.1.0",
+		"@wordpress/widgets": "1.1.1",
 		"@wordpress/wordcount": "3.1.0",
 		"backbone": "1.4.0",
 		"clipboard": "2.0.8",

src/wp-admin/admin-header.php

@@ -190,8 +190,7 @@
 $admin_body_class .= ' no-customize-support no-svg';
 
 if ( $current_screen->is_block_editor() ) {
-	// Default to is-fullscreen-mode to avoid jumps in the UI.
-	$admin_body_class .= ' block-editor-page is-fullscreen-mode wp-embed-responsive';
+	$admin_body_class .= ' block-editor-page wp-embed-responsive';
 }
 
 $error_get_last = error_get_last();

src/wp-admin/edit-form-blocks.php

@@ -29,6 +29,14 @@
 $current_screen = get_current_screen();
 $current_screen->is_block_editor( true );
 
+// Default to is-fullscreen-mode to avoid jumps in the UI.
+add_filter(
+	'admin_body_class',
+	function( $classes ) {
+		return "$classes is-fullscreen-mode";
+	}
+);
+
 /*
  * Emoji replacement is disabled for now, until it plays nicely with React.
  */

src/wp-admin/widgets-form-blocks.php

@@ -0,0 +1,66 @@
+<?php
+/**
+ * The block-based widgets editor, for use in widgets.php.
+ *
+ * @package WordPress
+ * @subpackage Administration
+ */
+
+// Don't load directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	die( '-1' );
+}
+
+// Flag that we're loading the block editor.
+$current_screen = get_current_screen();
+$current_screen->is_block_editor( true );
+
+$block_editor_context = new WP_Block_Editor_Context();
+
+$preload_paths = array(
+	array( '/wp/v2/media', 'OPTIONS' ),
+	'/wp/v2/sidebars?context=edit&per_page=-1',
+	'/wp/v2/widgets?context=edit&per_page=-1&_embed=about',
+);
+block_editor_rest_api_preload( $preload_paths, $block_editor_context );
+
+$editor_settings = get_block_editor_settings( array(), $block_editor_context );
+
+wp_add_inline_script(
+	'wp-edit-widgets',
+	sprintf(
+		'wp.domReady( function() {
+			wp.editWidgets.initialize( "widgets-editor", %s );
+		} );',
+		wp_json_encode( $editor_settings )
+	)
+);
+
+// Preload server-registered block schemas.
+wp_add_inline_script(
+	'wp-blocks',
+	'wp.blocks.unstable__bootstrapServerSideBlockDefinitions(' . wp_json_encode( get_block_editor_server_block_settings() ) . ');'
+);
+
+wp_add_inline_script(
+	'wp-blocks',
+	sprintf( 'wp.blocks.setCategories( %s );', wp_json_encode( get_block_categories( 'widgets-editor' ) ) ),
+	'after'
+);
+
+wp_enqueue_script( 'wp-edit-widgets' );
+wp_enqueue_script( 'admin-widgets' );
+wp_enqueue_script( 'wp-format-library' );
+wp_enqueue_style( 'wp-edit-widgets' );
+wp_enqueue_style( 'wp-format-library' );
+
+/** This action is documented in edit-form-blocks.php */
+do_action( 'enqueue_block_editor_assets' );
+
+require_once ABSPATH . 'wp-admin/admin-header.php';
+?>
+
+<div id="widgets-editor" class="blocks-widgets-container"></div> 
+
+<?php
+require_once ABSPATH . 'wp-admin/admin-footer.php';