Add a TImezone validation rule

Author: riasvdv

src/Shared/Rules/TimezoneRule.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace CraftCms\Cms\Shared\Rules;
+
+use Closure;
+use CraftCms\Cms\Support\Env;
+use Illuminate\Contracts\Validation\ValidationRule;
+use IntlDateFormatter;
+use IntlException;
+
+final readonly class TimezoneRule implements ValidationRule
+{
+    public function validate(string $attribute, mixed $value, Closure $fail): void
+    {
+        $timezone = Env::parse($value);
+
+        try {
+            $formatter = new IntlDateFormatter(app()->getLocale(), IntlDateFormatter::NONE, IntlDateFormatter::NONE);
+
+            if (! $formatter->setTimeZone($timezone)) {
+                $timezone = 'UTC';
+                $fail("Time zone “{$timezone}” does not appear to be supported by ICU.");
+            }
+        } catch (IntlException) {
+            $fail("Time zone “{$timezone}” does not appear to be supported by ICU: ".intl_get_error_message());
+        }
+    }
+}