Issue #3231996: Ensure file system is writeable

src/Validator/WritableFileSystemValidator.php

@@ -20,14 +20,24 @@ class WritableFileSystemValidator implements EventSubscriberInterface {
    */
   protected $pathLocator;
 
+  /**
+   * The Drupal root.
+   *
+   * @var string
+   */
+  protected $appRoot;
+
   /**
    * Constructs a WritableFileSystemValidator object.
    *
    * @param \Drupal\automatic_updates\PathLocator $path_locator
    *   The path locator service.
+   * @param string $app_root
+   *   The Drupal root.
    */
-  public function __construct(PathLocator $path_locator) {
+  public function __construct(PathLocator $path_locator, string $app_root) {
     $this->pathLocator = $path_locator;
+    $this->appRoot = $app_root;
   }
 
   /**
@@ -35,21 +45,19 @@ class WritableFileSystemValidator implements EventSubscriberInterface {
    *
    * @param \Drupal\automatic_updates\Event\UpdateEvent $event
    *   The event object.
+   *
+   * @todo It might make sense to use a more sophisticated method of testing
+   *   writability than is_writable(), since it's not clear if that can return
+   *   false negatives/positives due to things like SELinux, exotic file
+   *   systems, and so forth.
    */
   public function checkPermissions(UpdateEvent $event): void {
     $messages = [];
 
-    $dir = $this->pathLocator->getProjectRoot();
-    if (!is_writable($dir)) {
-      $messages[] = $this->t('The project directory "@dir" is not writable.', ['@dir' => $dir]);
-    }
-
-    $web_root = $this->pathLocator->getWebRoot();
-    if ($web_root) {
-      $dir .= DIRECTORY_SEPARATOR . $web_root;
-      if (!is_writable($dir)) {
-        $messages[] = $this->t('The Drupal directory "@dir" is not writable.', ['@dir' => $dir]);
-      }
+    if (!is_writable($this->appRoot)) {
+      $messages[] = $this->t('The Drupal directory "@dir" is not writable.', [
+        '@dir' => $this->appRoot,
+      ]);
     }
 
     $dir = $this->pathLocator->getVendorDirectory();