Backport: opt out for Navigation fallback creation

src/wp-includes/class-wp-navigation-fallback.php

@@ -26,9 +26,18 @@ class WP_Navigation_Fallback {
 	 */
 	public static function get_fallback() {
 
+		/**
+		 * Filters whether or not a fallback should be created.
+		 *
+		 * @since 6.3.0
+		 *
+		 * @param bool Whether or not to create a fallback.
+		 */
+		$should_create_fallback = apply_filters( 'wp_navigation_should_create_fallback', true );
+
 		$fallback = static::get_most_recently_published_navigation();
 
-		if ( $fallback ) {
+		if ( $fallback || ! $should_create_fallback ) {
 			return $fallback;
 		}
 

tests/phpunit/tests/editor/navigation-fallback.php

@@ -56,6 +56,25 @@ public function test_should_return_a_default_fallback_navigation_menu_in_absence
 		$this->assertCount( 1, $navs_in_db, 'The fallback Navigation post should be the only one in the database.' );
 	}
 
+	/**
+	 * @ticket 58557
+	 * @covers WP_REST_Navigation_Fallback_Controller::get_fallback
+	 */
+	public function test_should_not_automatically_create_fallback_if_filter_is_falsey() {
+
+		add_filter( 'gutenberg_navigation_should_create_fallback', '__return_false' );
+
+		$data = Gutenberg_Navigation_Fallback::get_fallback();
+
+		$this->assertEmpty( $data );
+
+		$navs_in_db = $this->get_navigations_in_database();
+
+		$this->assertCount( 0, $navs_in_db, 'The fallback Navigation post should not have been created.' );
+
+		remove_filter( 'gutenberg_navigation_should_create_fallback', '__return_false' );
+	}
+
 	/**
 	 * @ticket 58557
 	 * @covers WP_REST_Navigation_Fallback_Controller::get_fallback