Widgets: Match variable types in rss feed link filter.

The `rss_widget_feed_link` filter added in [52031] documents the parameter as a string, but recommends removing by returning false. Change the recommendation and documentation to make this consistent and update Twenty Twenty One to use the new recommended return value. Maintains documentation as possibly returning `false` for backwards compatibility.

Props sabernhardt, Mista-Flo.
Fixes #57594.

git-svn-id: https://develop.svn.wordpress.org/trunk@55409 602fd350-edb4-49c9-b593-d223f7449a82

Author: joedolson

src/wp-content/themes/twentytwentyone/functions.php

@@ -340,7 +340,7 @@ function twenty_twenty_one_setup() {
 		add_theme_support( 'custom-units' );
 
 		// Remove feed icon link from legacy RSS widget.
-		add_filter( 'rss_widget_feed_link', '__return_false' );
+		add_filter( 'rss_widget_feed_link', '__return_empty_string' );
 	}
 }
 add_action( 'after_setup_theme', 'twenty_twenty_one_setup' );

src/wp-includes/widgets/class-wp-widget-rss.php

@@ -101,12 +101,12 @@ public function widget( $args, $instance ) {
 			/**
 			 * Filters the classic RSS widget's feed icon link.
 			 *
-			 * Themes can remove the icon link by using `add_filter( 'rss_widget_feed_link', '__return_false' );`.
+			 * Themes can remove the icon link by using `add_filter( 'rss_widget_feed_link', '__return_empty_string' );`.
 			 *
 			 * @since 5.9.0
 			 *
-			 * @param string $feed_link HTML for link to RSS feed.
-			 * @param array  $instance  Array of settings for the current widget.
+			 * @param string|false $feed_link HTML for link to RSS feed.
+			 * @param array        $instance  Array of settings for the current widget.
 			 */
 			$feed_link = apply_filters( 'rss_widget_feed_link', $feed_link, $instance );