Set Anonymous timezone to match site default

Just looking at this and from what I can see the behaviour seems to be related to the use of date_default_timezone_set() and date_default_timezone_get()

date_default_timezone_get — Gets the default timezone used by all date/time functions in a script

Description ¶

date_default_timezone_get(): string
In order of preference, this function returns the default timezone by:

Reading the timezone set using the date_default_timezone_set() function (if any)

Reading the value of the date.timezone ini option (if set)

If none of the above succeed, date_default_timezone_get() will return a default timezone of UTC.

https://www.php.net/manual/en/function.date-default-timezone-get.php

date_default_timezone_set() is called correctly for logged in users. In fact when tested this it appears to be called 4 times on a single page with a single node. (submitted on), compared to just once for an anonymous user! ?

Looking at php.info at has a value called date.timezone and this seems to be the same value that is being returned for anonymous user, despite date_default_timezone_set being called in an almost identical fashion to logged in users.

Now when I step through the code as an anonymous user, I can see that date_default_timezone_set() is called in
web/core/modules/system/src/TimeZoneResolver.php

Call stack:

Drupal\system\TimeZoneResolver->setDefaultTimeZone (/web/core/modules/system/src/TimeZoneResolver.php:53)
call_user_func:{/var/www/html/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php:111} (/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php:111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch (/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php:111)
Symfony\Component\HttpKernel\HttpKernel->handleRaw (/vendor/symfony/http-kernel/HttpKernel.php:157)
Symfony\Component\HttpKernel\HttpKernel->handle (/vendor/symfony/http-kernel/HttpKernel.php:76)
Drupal\Core\StackMiddleware\Session->handle (/web/core/lib/Drupal/Core/StackMiddleware/Session.php:58)
Drupal\Core\StackMiddleware\KernelPreHandle->handle (/web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php:48)
Drupal\Core\StackMiddleware\ContentLength->handle (/web/core/lib/Drupal/Core/StackMiddleware/ContentLength.php:28)
Drupal\big_pipe\StackMiddleware\ContentLength->handle (/web/core/modules/big_pipe/src/StackMiddleware/ContentLength.php:32)
Drupal\page_cache\StackMiddleware\PageCache->fetch (/web/core/modules/page_cache/src/StackMiddleware/PageCache.php:191)
Drupal\page_cache\StackMiddleware\PageCache->lookup (/web/core/modules/page_cache/src/StackMiddleware/PageCache.php:128)
Drupal\page_cache\StackMiddleware\PageCache->handle (/web/core/modules/page_cache/src/StackMiddleware/PageCache.php:82)
Drupal\ban\BanMiddleware->handle (/web/core/modules/ban/src/BanMiddleware.php:50)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle (/web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php:48)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle (/web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php:51)
Drupal\Core\StackMiddleware\AjaxPageState->handle (/web/core/lib/Drupal/Core/StackMiddleware/AjaxPageState.php:36)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle (/web/core/lib/Drupal/Core/StackMiddleware/StackedHttpKernel.php:51)
Drupal\Core\DrupalKernel->handle (/web/core/lib/Drupal/Core/DrupalKernel.php:704)
{main} (/web/index.php:19)

However, When I am logged in setDefaultTimeZone is called 4 times. Here is the call stack the last time it is called

Drupal\system\TimeZoneResolver->setDefaultTimeZone (/web/core/modules/system/src/TimeZoneResolver.php:53)
call_user_func:{/var/www/html/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php:111} (/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php:111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch (/web/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php:111)
Symfony\Component\HttpKernel\HttpKernel->handleRaw (/vendor/symfony/http-kernel/HttpKernel.php:157)
Symfony\Component\HttpKernel\HttpKernel->handle (/vendor/symfony/http-kernel/HttpKernel.php:76)
Drupal\Core\StackMiddleware\Session->handle (/web/core/lib/Drupal/Core/StackMiddleware/Session.php:58)
Drupal\Core\StackMiddleware\KernelPreHandle->handle (/web/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php:48)
Drupal\Core\StackMiddleware\ContentLength->handle (/web/core/lib/Drupal/Core/StackMiddleware/ContentLength.php:28)
Drupal\big_pipe\StackMiddleware\ContentLength->handle (/web/core/modules/big_pipe/src/StackMiddleware/ContentLength.php:32)
Drupal\page_cache\StackMiddleware\PageCache->pass (/web/core/modules/page_cache/src/StackMiddleware/PageCache.php:106)
Drupal\page_cache\StackMiddleware\PageCache->handle (/web/core/modules/page_cache/src/StackMiddleware/PageCache.php:85)
Drupal\ban\BanMiddleware->handle (/web/core/modules/ban/src/BanMiddleware.php:50)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle (/web/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php:48)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle (/web/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php:51)
Drupal\Core\StackMiddleware\AjaxPageState->handle (/web/core/lib/Drupal/Core/StackMiddleware/AjaxPageState.php:36)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle (/web/core/lib/Drupal/Core/StackMiddleware/StackedHttpKernel.php:51)
Drupal\Core\DrupalKernel->handle (/web/core/lib/Drupal/Core/DrupalKernel.php:704)
{main} (/web/index.php:19)

Also, I did see this clue in web/core/lib/Drupal/Core/Cache/Context/TimeZoneCacheContext.php

  /**
   * {@inheritdoc}
   */
  public function getContext() {
    // date_default_timezone_set() is called in AccountProxy::setAccount(), so
    // we can safely retrieve the timezone.
    return date_default_timezone_get();
  }

OK events for logged in user are

account.set
kernel.request

account.set
kernel.request

for anonymous user it is just kernel.request

Ok this is a bit embarrassing.

I have looked at this again and it seems to be working as expected now. 😊

Updated time for anonymous user seems to be the same as that for logged in user both with user timezone and or site timezone set to local under local and regional settings/config.

Thanks.