[REST] Restore the missing double slash in the ID received by /templates

lib/compat/wordpress-5.9/class-gutenberg-rest-templates-controller.php

@@ -67,8 +67,9 @@ public function register_routes() {
 					'permission_callback' => array( $this, 'get_item_permissions_check' ),
 					'args'                => array(
 						'id' => array(
-							'description' => __( 'The id of a template', 'gutenberg' ),
-							'type'        => 'string',
+							'description'       => __( 'The id of a template', 'gutenberg' ),
+							'type'              => 'string',
+							'sanitize_callback' => array( $this, '_sanitize_template_id' ),
 						),
 					),
 				),
@@ -116,6 +117,36 @@ protected function permissions_check() {
 		return true;
 	}
 
+	/**
+	 * Requesting this endpoint for a template like "twentytwentytwo//home" requires using
+	 * a path like /wp/v2/templates/twentytwentytwo//home. There are special cases when
+	 * WordPress routing corrects the name to contain only a single slash like "twentytwentytwo/home".
+	 *
+	 * This method doubles the last slash if it's not already doubled. It relies on the template
+	 * ID format {theme_name}//{template_slug} and the fact that slugs cannot contain slashes.
+	 *
+	 * See https://core.trac.wordpress.org/ticket/54507 for more context
+	 *
+	 * @param string $id Template ID.
+	 * @return string Sanitized template ID.
+	 */
+	public function _sanitize_template_id( $id ) {
+		$last_slash_pos = strrpos( $id, '/' );
+		if ( false === $last_slash_pos ) {
+			return $id;
+		}
+
+		$is_double_slashed = substr( $id, $last_slash_pos - 1, 1 ) === '/';
+		if ( $is_double_slashed ) {
+			return $id;
+		}
+		return (
+			substr( $id, 0, $last_slash_pos )
+			. '/'
+			. substr( $id, $last_slash_pos )
+		);
+	}
+
 	/**
 	 * Checks if a given request has access to read templates.
 	 *

phpunit/class-gutenberg-rest-template-controller-test.php

@@ -160,6 +160,76 @@ public function test_get_item() {
 		);
 	}
 
+	/**
+	 * Ticket 54507
+	 *
+	 * @dataProvider template_endpoint_urls
+	 */
+	public function test_get_item_works_with_a_single_slash( $endpoint_url ) {
+		wp_set_current_user( self::$admin_id );
+		$request  = new WP_REST_Request( 'GET', $endpoint_url );
+		$response = rest_get_server()->dispatch( $request );
+
+		$data = $response->get_data();
+		unset( $data['content'] );
+		unset( $data['_links'] );
+
+		$this->assertEquals(
+			array(
+				'id'             => 'tt1-blocks//index',
+				'theme'          => 'tt1-blocks',
+				'slug'           => 'index',
+				'title'          => array(
+					'raw'      => 'Index',
+					'rendered' => 'Index',
+				),
+				'description'    => 'The default template used when no other template is available. This is a required template in WordPress.',
+				'status'         => 'publish',
+				'source'         => 'theme',
+				'type'           => 'wp_template',
+				'wp_id'          => null,
+				'has_theme_file' => true,
+			),
+			$data
+		);
+	}
+
+	/**
+	 *
+	 */
+	public function template_endpoint_urls() {
+		return array(
+			array( '/wp/v2/templates/tt1-blocks/index' ),
+			array( '/wp/v2/templates/tt1-blocks//index' ),
+		);
+	}
+
+	/**
+	 * Ticket 54507
+	 *
+	 * @dataProvider get_template_ids_to_sanitize
+	 */
+	public function test_sanitize_template_id( $input_id, $sanitized_id ) {
+		$endpoint = new Gutenberg_REST_Templates_Controller( 'wp_template' );
+		$this->assertEquals(
+			$sanitized_id,
+			$endpoint->_sanitize_template_id( $input_id )
+		);
+	}
+
+	/**
+	 *
+	 */
+	public function get_template_ids_to_sanitize() {
+		return array(
+			array( 'tt1-blocks/index', 'tt1-blocks//index' ),
+			array( 'tt1-blocks//index', 'tt1-blocks//index' ),
+
+			array( 'theme-experiments/tt1-blocks/index', 'theme-experiments/tt1-blocks//index' ),
+			array( 'theme-experiments/tt1-blocks//index', 'theme-experiments/tt1-blocks//index' ),
+		);
+	}
+
 	public function test_create_item() {
 		wp_set_current_user( self::$admin_id );
 		$request = new WP_REST_Request( 'POST', '/wp/v2/templates' );