Bug: CodeIgniter\Router\RouteCollection->fillRouteParams() ErrorException on 'from' parameter containing regex pattern with '|' symbol

[bivanbi]

CodeIgniter\Router\RouteCollection->fillRouteParams() uses '|' as delimiter for preg_match call. This is likely to result in ErrorException or incorrect pattern matching if the pattern itself actually contains '|' character as preg_match treats all the following characters as modifiers.

This is also inconsistent with CodeIgniter\Router->checkRoutes() which uses '#' as delimiter, and is working as expected.

CodeIgniter 4 version
Release: 4.0.3
Develop: 6bd43bb

Affected module(s)
CodeIgniter\Router\RouteCollection

Expected behavior, and steps to reproduce if appropriate

1. Create a named route with regular expression in 'from' parameter like this:
   $routes->get('system/(this|that)', 'SomeController::someMethod/$1', ['as' => 'this-or-that']);

2. Verify that route is correctly processed by accessing /system/this and /system/that URI in a browser

3. Call route_to('this-or-that', 'this');

Expected:
route_to() returns string '/system/this'

Actual:
Exception: ErrorException: preg_match(): Unknown modifier 't' in /php/system/Router/RouteCollection.php:1351

Context

• OS: Ubuntu 18.04.4
• Web server: Apache 2.4.29
• PHP version: 7.2.24