REST API: add JsonSerializable() compatibility interface for PHP <5.4 to compat.php

Props rmmcue.
See #33982.


git-svn-id: https://develop.svn.wordpress.org/trunk@34845 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/compat.php

@@ -315,4 +315,20 @@ if ( ! function_exists( 'json_last_error_msg' ) ) :
 				return 'An unknown error occurred';
 		}
 	}
-endif;
+endif;
+
+if ( ! interface_exists( 'JsonSerializable' ) ) {
+	define( 'WP_JSON_SERIALIZE_COMPATIBLE', true );
+	/**
+	 * JsonSerializable interface.
+	 *
+	 * Compatibility shim for PHP <5.4
+	 *
+     * @link http://php.net/jsonserializable
+	 *
+	 * @since 4.4.0
+	 */
+	interface JsonSerializable {
+		public function jsonSerialize();
+	}
+}