Issue #3023903: Allow config override directory to be stored outside of Drupal.

src/SiteConfigOverrides.php

@@ -7,6 +7,7 @@ use Drupal\Core\Cache\CacheBackendInterface;
 use Drupal\Core\Config\ConfigFactoryOverrideInterface;
 use Drupal\Core\Config\FileStorage;
 use Drupal\Core\Config\StorageInterface;
+use Drupal\Core\Site\Settings;
 
 /**
  * Site configuration overrides service.
@@ -50,9 +51,9 @@ class SiteConfigOverrides implements ConfigFactoryOverrideInterface {
    */
   public function loadOverrides($names) {
     $overrides = [];
-    $directory;
+    $directory = $this->getSiteConfigOverrideFolder();
 
-    if (!$directory = $this->getSiteConfigOverrideFolder()) {
+    if (!file_exists($directory)) {
       return $overrides;
     }
 
@@ -76,7 +77,7 @@ class SiteConfigOverrides implements ConfigFactoryOverrideInterface {
    */
   protected function getSiteConfigOverrideFolder() {
     try {
-      return $this->root . '/' . $this->configGetConfigDirectory(static::CONFIG_OVERRIDE_DIRECTORY);
+      return Settings::get(static::CONFIG_OVERRIDE_DIRECTORY, $this->root . '/' . $this->configGetConfigDirectory(static::CONFIG_OVERRIDE_DIRECTORY));
     }
     catch (\Exception $e) {
       return NULL;