Add deprecation and documentation

docs/reference/configuration.rst

@@ -10,6 +10,15 @@ Timezone detectors
 User timezone detector
 ^^^^^^^^^^^^^^^^^^^^^^
 
+.. versionadded:: 2.x
+
+    If the model class for the authenticated user implements ``Sonata\IntlBundle\Timezone\TimezoneAwareInterface``,
+    it returns the timezone from its ``getTimezone()`` method.
+
+**DEPRECATED**
+Relying on ``Sonata\UserBundle\Model\User`` is deprecated since 2.x in favor of
+explicit implementation of ``Sonata\IntlBundle\Timezone\TimezoneAwareInterface``.
+
 If the SonataUserBundle_ is enabled, it returns the timezone from the
 ``Sonata\UserBundle\Model\User::getTimezone()`` method.
 

src/Timezone/UserBasedTimezoneDetector.php

@@ -49,6 +49,13 @@ public function getTimezone()
 
         // NEXT_MAJOR: Remove this check when `User` implement `TimezoneAwareInterface`
         if ($user instanceof User) {
+            @trigger_error(sprintf(
+                'Timezone inference based on the %s class is deprecated since sonata-project/intl-bundle 2.7 and will be dropped in 3.0 version.'
+                .' Implement %s explicitely in your user class instead.',
+                User::class,
+                TimezoneAwareInterface::class
+            ), E_USER_DEPRECATED);
+
             return $user->getTimezone();
         }