Drupal 8 Passing global variables from settings.php to twig and/or js files

i really wondering how to pass my variable globaly (page level) so it can be used anywhere.

What i have done:

on my group vars > dev.yml

link: "www.anylink.com"

on my group vars > prod.yml

link: "www.anylink-prod.com"

on my settings.php (j2)

$settings["custom_link"]={{link}};

on my template.theme

function theme_preprocess_page(&$variables) {
  $variables[theme_link] = Settings::get('custom_link');
}

on my twig {{ theme_link }}

but it really doesn't print any string from my prod/dev.yml.. i was wondering what is wrong?

my main aim doing this is,

i want to have a links that print depends on what environment i am on. hopefully anybody can light me up on this problem, THank you !

Solution

For global twig varibales:

The OOP way without using HOOKs:

create a RequestListener placed in (MY_MODULE/src/Event/Listener):

<?php

namespace Drupal\<MY_MODULE>\Event\Listener;

use Drupal\Core\Site\Settings;
use Drupal\Core\Template\TwigEnvironment;
use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\HttpKernel\Event\GetResponseEvent;
use Symfony\Component\HttpKernel\KernelEvents;

/**
 * Class MyRequestListener
 *
 */
class MyRequestListener implements EventSubscriberInterface {

  /**
   * @var \Drupal\Core\Template\TwigEnvironment
   */
  protected $twigEnvironment;

  /**
   * @var \Drupal\Core\Site\Settings
   */
  protected $settings;


  /**
   * FdeRequestListener constructor.
   */
  public function __construct(TwigEnvironment $twigEnvironment,
                              Settings $settings) {

    $this->twigEnvironment = $twigEnvironment;
    $this->settings        = $settings;
  }

  /**
   * @return mixed
   */
  public static function getSubscribedEvents() {
    $events[KernelEvents::REQUEST][] = ['onRequest'];
    return $events;
  }

  /**
   * @param GetResponseEvent $e
   */
  public function onRequest(GetResponseEvent $e) {
    //here you can add everything which is then globally accessible in twig templates like {{ custom_link }}
    $this->twigEnvironment->addGlobal('custom_link', $this->settings->get('custom_link'));
  }

}

and you have to register it as a service in your MY_MODULE.service.yml like:

my_requestlistener:
  class: Drupal\<MY_MODULE>\Event\Listener\MyRequestListener
  arguments:
    - @twig
    - @settings

for global JS settings:

create a hook in your MY_MODULE.module file:

<?php
/**
 * Implements hook_js_settings_alter().
 * - adds "custom_link" to the drupalSettings
 */
function my_module_js_settings_alter(array &$settings,
    \Drupal\Core\Asset\AttachedAssetsInterface $assets
) {
      /* @var $settings Drupal\Core\Site\Settings */
      $globalSettings = \Drupal::service('settings');

      //if you want to push all settings into drupalSettings JS object
      $settings['all_settings'] = $globalSettings->getAll();
      //if you want to push only a single value
      $settings['custom_link'] = $globalSettings->get('custom_link')

 }