Return a cacheable response from TimezoneController

Closes #3514879

core/modules/system/src/Controller/TimezoneController.php

@@ -2,7 +2,8 @@
 
 namespace Drupal\system\Controller;
 
-use Symfony\Component\HttpFoundation\JsonResponse;
+use Drupal\Core\Cache\CacheableJsonResponse;
+use Drupal\Core\Cache\CacheableMetadata;
 
 /**
  * Provides a callback for finding a time zone identifier.
@@ -23,15 +24,19 @@ class TimezoneController {
    *   Daylight saving time indicator. If abbreviation does not exist then the
    *   time zone is searched solely by offset and is DST.
    *
-   * @return \Symfony\Component\HttpFoundation\JsonResponse
-   *   The time zone identifier or 'false' in JsonResponse object.
+   * @return \Drupal\Core\Cache\CacheableJsonResponse
+   *   The time zone identifier or 'false' in CacheableJsonResponse object.
    */
   public function getTimezone($abbreviation = '', $offset = -1, $is_daylight_saving_time = NULL) {
     $offset = intval($offset);
+
+    // All timezone responses are cacheable based on the route.
+    $cacheable_metadata = (new CacheableMetadata())->addCacheContexts(['route']);
+
     // Out of bounds check for offset. Offset +/- UTC is typically no
     // smaller/larger than -12/+14.
     if ($offset < -60000 || $offset > 60000) {
-      return new JsonResponse(FALSE);
+      return (new CacheableJsonResponse(FALSE))->addCacheableDependency($cacheable_metadata);
     }
 
     if (isset($is_daylight_saving_time)) {
@@ -39,15 +44,20 @@ public function getTimezone($abbreviation = '', $offset = -1, $is_daylight_savin
       $is_daylight_saving_time = min(1, max(-1, intval($is_daylight_saving_time)));
       // Catch if out of boundary.
       if ($original !== $is_daylight_saving_time) {
-        return new JsonResponse(FALSE);
+        return (new CacheableJsonResponse(FALSE))->addCacheableDependency($cacheable_metadata);
       }
     }
+    else {
+      // If no daylight saving time indicator was specified, default to -1
+      // to indicate that daylight saving was not taken into consideration.
+      $is_daylight_saving_time = -1;
+    }
 
     // An abbreviation of "0" passed in the callback arguments should be
     // interpreted as the empty string.
     $abbreviation = $abbreviation ?: '';
     $timezone = timezone_name_from_abbr($abbreviation, $offset, $is_daylight_saving_time);
-    return new JsonResponse($timezone);
+    return (new CacheableJsonResponse($timezone))->addCacheableDependency($cacheable_metadata);
   }
 
 }

[Stephen Mustgrave]

This part is the only thing I'm not sure about, seems to be addressing another issue maybe?

[Daniel Pfeiffer]

It is addressing a different issue, but it's somewhat a prerequisite to get caching to work.

Without this, $is_daylight_saving_time can be NULL when it is passed to timezone_name_from_abbr. As of PHP 8, this will generate a deprecation notice. And, depending on the current settings, a PHP notice will add a message to Messenger which will trigger the page cache KillSwitch (see Messenger::addMessage).

So, while the controller can return a cacheable response without this change, the response will likely not end up getting cached due to the PHP notice.