Edit site: prevent enqueuing entire stylesheet in iframe

lib/compat/wordpress-6.4/script-loader.php

@@ -96,3 +96,92 @@ function gutenberg_update_wp_date_settings( $scripts ) {
 
 add_action( 'wp_default_scripts', 'gutenberg_update_wp_date_settings' );
 
+/**
+ * Collect the block editor assets that need to be loaded into the editor's iframe.
+ *
+ * @since 6.0.0
+ * @access private
+ *
+ * @return array {
+ *     The block editor assets.
+ *
+ *     @type string|false $styles  String containing the HTML for styles.
+ *     @type string|false $scripts String containing the HTML for scripts.
+ * }
+ */
+function _gutenberg_get_iframed_editor_assets_6_4() {
+	global $wp_styles, $wp_scripts;
+
+	// Keep track of the styles and scripts instance to restore later.
+	$current_wp_styles  = $wp_styles;
+	$current_wp_scripts = $wp_scripts;
+
+	// Create new instances to collect the assets.
+	$wp_styles  = new WP_Styles();
+	$wp_scripts = new WP_Scripts();
+
+	// Register all currently registered styles and scripts. The actions that
+	// follow enqueue assets, but don't necessarily register them.
+	$wp_styles->registered  = $current_wp_styles->registered;
+	$wp_scripts->registered = $current_wp_scripts->registered;
+
+	// We generally do not need reset styles for the iframed editor.
+	// However, if it's a classic theme, margins will be added to every block,
+	// which is reset specifically for list items, so classic themes rely on
+	// these reset styles.
+	$wp_styles->done =
+		wp_theme_has_theme_json() ? array( 'wp-reset-editor-styles' ) : array();
+
+	wp_enqueue_script( 'wp-polyfill' );
+	// Enqueue the `editorStyle` handles for all core block, and dependencies.
+	wp_enqueue_style( 'wp-edit-blocks' );
+
+	if ( current_theme_supports( 'wp-block-styles' ) ) {
+		wp_enqueue_style( 'wp-block-library-theme' );
+	}
+
+	// We don't want to load EDITOR scripts in the iframe, only enqueue
+	// front-end assets for the content.
+	add_filter( 'should_load_block_editor_scripts_and_styles', '__return_false' );
+	do_action( 'enqueue_block_assets' );
+	remove_filter( 'should_load_block_editor_scripts_and_styles', '__return_false' );
+
+	$block_registry = WP_Block_Type_Registry::get_instance();
+
+	// Additionally, do enqueue `editorStyle` assets for all blocks, which
+	// contains editor-only styling for blocks (editor content).
+	foreach ( $block_registry->get_all_registered() as $block_type ) {
+		if ( isset( $block_type->editor_style_handles ) && is_array( $block_type->editor_style_handles ) ) {
+			foreach ( $block_type->editor_style_handles as $style_handle ) {
+				wp_enqueue_style( $style_handle );
+			}
+		}
+	}
+
+	ob_start();
+	wp_print_styles();
+	$styles = ob_get_clean();
+
+	ob_start();
+	wp_print_head_scripts();
+	wp_print_footer_scripts();
+	$scripts = ob_get_clean();
+
+	// Restore the original instances.
+	$wp_styles  = $current_wp_styles;
+	$wp_scripts = $current_wp_scripts;
+
+	return array(
+		'styles'  => $styles,
+		'scripts' => $scripts,
+	);
+}
+
+add_filter(
+	'block_editor_settings_all',
+	static function( $settings ) {
+		// We must override what core is passing now.
+		$settings['__unstableResolvedAssets'] = _gutenberg_get_iframed_editor_assets_6_4();
+		return $settings;
+	}
+);

packages/edit-site/src/components/sidebar-navigation-screen-navigation-menus/style.scss

@@ -90,10 +90,6 @@
 	}
 }
 
-.edit-site-sidebar-navigation-screen-navigation-menus__content .popover-slot .wp-block-navigation-submenu {
-	display: none;
-}
-
 .edit-site-sidebar-navigation-screen-navigation-menus__loading.components-spinner {
 	margin-left: auto;
 	margin-right: auto;