manager-bundle/src/Routing/RouteLoader.php
public function loadFromPlugins(): RouteCollection
    {
        $collection = array_reduce(
            $this->pluginLoader->getInstancesOf(PluginLoader::ROUTING_PLUGINS, true),
            function (RouteCollection $collection, RoutingPluginInterface $plugin): RouteCollection {
                $routes = $plugin->getRouteCollection($this->loader->getResolver(), $this->kernel);

                if ($routes instanceof RouteCollection) {
                    $collection->addCollection($routes);
                }

                return $collection;
            },
            new RouteCollection()
        );

        // Load the app/config/routing.yml file if it exists
        if (file_exists($configFile = $this->rootDir.'/app/config/routing.yml')) {
            $routes = $this->loader->getResolver()->resolve($configFile)->load($configFile);

            if ($routes instanceof RouteCollection) {
                $collection->addCollection($routes);
            }
        }

        // Make sure the Contao frontend routes are always loaded last
        foreach (['contao_frontend', 'contao_index', 'contao_root', 'contao_catch_all'] as $name) {
            if ($route = $collection->get($name)) {
                $collection->add($name, $route);
            }
        }

        return $collection;
    }
public function loadFromPlugins(): RouteCollection
    {
        $collection = array_reduce(
            $this->pluginLoader->getInstancesOf(PluginLoader::ROUTING_PLUGINS, true),
            function (RouteCollection $collection, RoutingPluginInterface $plugin): RouteCollection {
                $routes = $plugin->getRouteCollection($this->loader->getResolver(), $this->kernel);

                if ($routes instanceof RouteCollection) {
                    $collection->addCollection($routes);
                }

                return $collection;
            },
            new RouteCollection()
        );

        // Load the app/config/routing.yml file if it exists
        if (file_exists($configFile = $this->rootDir.'/app/config/routing.yml')) {
            $routes = $this->loader->getResolver()->resolve($configFile)->load($configFile);

            if ($routes instanceof RouteCollection) {
                $collection->addCollection($routes);
            }
        }

        // Make sure the Contao frontend routes are always loaded last
        foreach (['contao_frontend', 'contao_index', 'contao_root', 'contao_catch_all'] as $name) {
            if ($route = $collection->get($name)) {
                $collection->add($name, $route);
            }
        }

        return $collection;
    }
Returns a route collection build from all plugin routes.