Widgets editor: Improve compatibility with WP 5.8

lib/compat/wordpress-5.8/index.php

@@ -12,6 +12,7 @@
 }
 
 require_once __DIR__ . '/block-editor.php';
+require_once __DIR__ . '/widgets.php';
 
 if ( ! function_exists( 'build_query_vars_from_query_block' ) ) {
 	/**

lib/widgets-api.php → lib/compat/wordpress-5.8/widgets.php

@@ -1,8 +1,8 @@
 <?php
 /**
- * Functions for working with widgets in WordPress. These should ultimately live
- * in wp-includes/widgets.php, wp-admin/includes/widgets.php, etc. when merged
- * to Core.
+ * Functions for working with widgets in WordPress. These exist in core and
+ * should be removed when WordPress 5.8.0 becomes the lowest supported version
+ * by this plugin.
  *
  * @package gutenberg
  */
@@ -242,3 +242,26 @@ function gutenberg_get_widget_object( $id_base ) {
 		return null;
 	}
 }
+
+if ( ! function_exists( 'gutenberg_use_widgets_block_editor' ) ) {
+	/**
+	 * Whether or not to use the block editor to manage widgets. Defaults to true
+	 * unless a theme has removed support for widgets-block-editor or a plugin has
+	 * filtered the return value of this function.
+	 *
+	 * Can be removed when minimum WordPress version is 5.8.
+	 *
+	 * @return boolean Whether or not to use the block editor to manage widgets.
+	 */
+	function gutenberg_use_widgets_block_editor() {
+		/**
+		 * Filters whether or not to use the block editor to manage widgets.
+		 *
+		 * @param boolean $use_widgets_block_editor Whether or not to use the block editor to manage widgets.
+		 */
+		return apply_filters(
+			'gutenberg_use_widgets_block_editor',
+			get_theme_support( 'widgets-block-editor' )
+		);
+	}
+}

lib/init.php

@@ -30,7 +30,10 @@ function gutenberg_menu() {
 		'gutenberg'
 	);
 
-	if ( gutenberg_use_widgets_block_editor() ) {
+	if (
+		gutenberg_use_widgets_block_editor() &&
+		! function_exists( 'wp_use_widgets_block_editor' )
+	) {
 		add_theme_page(
 			__( 'Widgets', 'gutenberg' ),
 			__( 'Widgets', 'gutenberg' ),
@@ -113,7 +116,11 @@ function gutenberg_site_editor_menu() {
  * @param WP_Admin_Bar $wp_admin_bar Core class used to implement the Toolbar API.
  */
 function modify_admin_bar( $wp_admin_bar ) {
-	if ( gutenberg_use_widgets_block_editor() && $wp_admin_bar->get_node( 'widgets' ) !== null ) {
+	if (
+		gutenberg_use_widgets_block_editor() &&
+		! function_exists( 'wp_use_widgets_block_editor' ) &&
+		$wp_admin_bar->get_node( 'widgets' ) !== null
+	) {
 		$wp_admin_bar->add_menu(
 			array(
 				'id'   => 'widgets',
@@ -137,7 +144,10 @@ function modify_welcome_panel() {
 	ob_start();
 	wp_welcome_panel();
 	$welcome_panel = ob_get_clean();
-	if ( gutenberg_use_widgets_block_editor() ) {
+	if (
+		gutenberg_use_widgets_block_editor() &&
+		! function_exists( 'wp_use_widgets_block_editor' )
+	) {
 		echo str_replace(
 			admin_url( 'widgets.php' ),
 			admin_url( 'themes.php?page=gutenberg-widgets' ),
@@ -177,5 +187,4 @@ function register_site_icon_url( $response ) {
 
 add_filter( 'rest_index', 'register_site_icon_url' );
 
-add_theme_support( 'widgets-block-editor' );
 add_theme_support( 'block-templates' );

lib/load.php

@@ -71,15 +71,15 @@ function gutenberg_is_experiment_enabled( $name ) {
 	require __DIR__ . '/rest-api.php';
 }
 
-// We can't use class_exists( 'WP_Widget_Block' ) because core loads widgets
-// *after* plugins, so test for wp_use_widgets_block_editor() which we know
-// implies the existence of WP_Widget_Block.
+// These files can be removed when 5.8.0 is the minimum supported version by
+// this plugin.
 if ( ! function_exists( 'wp_use_widgets_block_editor' ) ) {
 	require_once __DIR__ . '/class-wp-widget-block.php';
+	require_once __DIR__ . '/widgets-page.php';
+	require __DIR__ . '/widgets.php';
+	require __DIR__ . '/widgets-customize.php';
 }
 
-require_once __DIR__ . '/widgets-page.php';
-
 require __DIR__ . '/compat.php';
 require __DIR__ . '/compat/wordpress-5.8/index.php';
 require __DIR__ . '/utils.php';
@@ -111,9 +111,6 @@ function gutenberg_is_experiment_enabled( $name ) {
 require __DIR__ . '/block-patterns.php';
 require __DIR__ . '/client-assets.php';
 require __DIR__ . '/demo.php';
-require __DIR__ . '/widgets.php';
-require __DIR__ . '/widgets-api.php';
-require __DIR__ . '/widgets-customize.php';
 require __DIR__ . '/navigation.php';
 require __DIR__ . '/navigation-page.php';
 require __DIR__ . '/experiments-page.php';

lib/widgets-customize.php

@@ -167,11 +167,7 @@ function gutenberg_widgets_customize_load_block_editor_scripts_and_styles( $is_b
 	return $is_block_editor_screen;
 }
 
-// Test for wp_use_widgets_block_editor(), as the existence of this in core
-// implies that the Customizer already supports the widgets block editor.
-if ( ! function_exists( 'wp_use_widgets_block_editor' ) ) {
-	add_action( 'customize_register', 'gutenberg_widgets_customize_register' );
-	add_filter( 'widget_customizer_setting_args', 'gutenberg_widgets_customize_add_unstable_instance', 10, 2 );
-	add_action( 'customize_controls_enqueue_scripts', 'gutenberg_customize_widgets_init' );
-	add_filter( 'should_load_block_editor_scripts_and_styles', 'gutenberg_widgets_customize_load_block_editor_scripts_and_styles' );
-}
+add_action( 'customize_register', 'gutenberg_widgets_customize_register' );
+add_filter( 'widget_customizer_setting_args', 'gutenberg_widgets_customize_add_unstable_instance', 10, 2 );
+add_action( 'customize_controls_enqueue_scripts', 'gutenberg_customize_widgets_init' );
+add_filter( 'should_load_block_editor_scripts_and_styles', 'gutenberg_widgets_customize_load_block_editor_scripts_and_styles' );

lib/widgets.php

@@ -25,25 +25,6 @@ function gutenberg_is_block_editor() {
 		);
 }
 
-/**
- * Whether or not to use the block editor to manage widgets. Defaults to true
- * unless a theme has removed support for widgets-block-editor or a plugin has
- * filtered the return value of this function.
- *
- * @return boolean Whether or not to use the block editor to manage widgets.
- */
-function gutenberg_use_widgets_block_editor() {
-	/**
-	 * Filters whether or not to use the block editor to manage widgets.
-	 *
-	 * @param boolean $use_widgets_block_editor Whether or not to use the block editor to manage widgets.
-	 */
-	return apply_filters(
-		'gutenberg_use_widgets_block_editor',
-		get_theme_support( 'widgets-block-editor' )
-	);
-}
-
 /**
  * Emulates the Widgets screen `admin_print_styles` when at the block editor
  * screen.
@@ -309,3 +290,5 @@ function gutenberg_set_show_instance_in_rest_on_core_widgets() {
 	}
 }
 add_action( 'widgets_init', 'gutenberg_set_show_instance_in_rest_on_core_widgets' );
+
+add_theme_support( 'widgets-block-editor' );

packages/block-library/src/legacy-widget/edit/preview.js

@@ -46,8 +46,7 @@ export default function Preview( { idBase, instance, isVisible } ) {
 						// TODO: This chokes when the query param is too big.
 						// Ideally, we'd render a <ServerSideRender>. Maybe by
 						// rendering one in an iframe via a portal.
-						src={ addQueryArgs( 'themes.php', {
-							page: 'gutenberg-widgets',
+						src={ addQueryArgs( 'widgets.php', {
 							'legacy-widget-preview': {
 								idBase,
 								instance,

packages/block-library/src/legacy-widget/index.php

@@ -50,21 +50,25 @@ function render_block_core_legacy_widget( $attributes ) {
 }
 
 /**
- * On application init this does two things:
- *
- * - Registers the 'core/legacy-widget' block.
- * - Intercepts any request with legacy-widget-preview in the query param and,
- *   if set, renders a page containing a preview of the requested Legacy Widget
- *   block.
+ * Registers the 'core/legacy-widget' block.
  */
-function init_legacy_widget_block() {
+function register_block_core_legacy_widget() {
 	register_block_type_from_metadata(
 		__DIR__ . '/legacy-widget',
 		array(
 			'render_callback' => 'render_block_core_legacy_widget',
 		)
 	);
+}
+
+add_action( 'init', 'register_block_core_legacy_widget' );
 
+/**
+ * Intercepts any request with legacy-widget-preview in the query param and, if
+ * set, renders a page containing a preview of the requested Legacy Widget
+ * block.
+ */
+function handle_legacy_widget_preview_iframe() {
 	if ( empty( $_GET['legacy-widget-preview'] ) ) {
 		return;
 	}
@@ -110,4 +114,10 @@ function init_legacy_widget_block() {
 	exit;
 }
 
-add_action( 'init', 'init_legacy_widget_block' );
+// Run handle_legacy_widget_preview_iframe() on 'init' at the same priority as
+// register_block_core_legacy_widget(). This ensures that the block will be
+// registered by time we intercept the iframe request. The priority will be 20
+// in the Gutenberg plugin (as opposed to 10 in Core) because of a find and
+// replace in Gutenberg's webpack config.
+$priority = has_action( 'init', 'register_block_core_legacy_widget' );
+add_action( 'init', 'handle_legacy_widget_preview_iframe', $priority );