\Drupal\Core\Routing\UrlMatcher is dead code

Should this be closed as a duplicate

No, this one is to deprecate UrlMatcher and use the one from Symfony
But second is about AccessAwareRouter polishing

Setting needs work for change record and proper deprecation of the class according https://www.drupal.org/about/core/policies/core-change-policies/drupal-d... →

+++ b/core/lib/Drupal/Core/Routing/Router.php
@@ -7,7 +7,8 @@
+use Symfony\Component\Routing\Matcher\UrlMatcher;

@@ -28,7 +29,7 @@
-class Router extends UrlMatcher implements RequestMatcherInterface, RouterInterface {
+class Router extends UrlMatcher implements RouterInterface {

+++ /dev/null
@@ -1,58 +0,0 @@
-class UrlMatcher extends BaseUrlMatcher {

Filed change record https://www.drupal.org/node/3339050 →

Btw core's UrlMatcher still very different implementation from SF one

  protected function getAttributes(Route $route, $name, array $attributes): array {
    if ($route instanceof RouteObjectInterface && is_string($route->getRouteKey())) {
      $name = $route->getRouteKey();
    }
    $attributes[RouteObjectInterface::ROUTE_NAME] = $name;
    $attributes[RouteObjectInterface::ROUTE_OBJECT] = $route;

    return $this->mergeDefaults($attributes, $route->getDefaults());
  }

SF code

    protected function getAttributes(Route $route, string $name, array $attributes): array
    {
        $defaults = $route->getDefaults();
        if (isset($defaults['_canonical_route'])) {
            $name = $defaults['_canonical_route'];
            unset($defaults['_canonical_route']);
        }
        $attributes['_route'] = $name;

        return $this->mergeDefaults($attributes, $defaults);
    }