[BUGFIX] Mitigate locale C in DateFormatter wrapping class

Since PHP 8.3.0RC3 [1] the `\IntlDateFormatter` throws a
`\IntlException` exception with the message:

    datefmt_create: invalid locale: U_ILLEGAL_ARGUMENT_ERROR

if an invalid locale is passed to the constructor. The value `C`
is considered as a non-valid locale, albeit it may be set.

This change introduces a fallback to `en-US` for the two methods
of the `\TYPO3\CMS\Core\Localization\DateFormatter` wrapping class,
if `C` is passed as locale.

`en-US` has been chosen as fallback because the TYPO3 locale class
`\TYPO3\CMS\Core\Localization\Locale` uses the same as fallback if
`C` is provided and additional tests are added to cover the same
behaviour.

Note: Other illegal locales are not handled and will allow the
      exception to bubble up with PHP8.3+.

[1] php/php-src@a80db7b52aa134bdc8b9841

Resolves: #102095
Releases: main, 12.4
Change-Id: I26d1ab74bd9dd659363320e191874f8526845158
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81335
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>

typo3/sysext/core/Classes/Localization/DateFormatter.php

@@ -36,6 +36,10 @@ class DateFormatter
     public function format(mixed $date, string|int $format, string|Locale $locale): string
     {
         $locale = (string)$locale;
+        // Use fallback locale if 'C' is provided.
+        if ($locale === 'C') {
+            $locale = 'en-US';
+        }
         if (is_int($format) || MathUtility::canBeInterpretedAsInteger($format)) {
             $dateFormatter = new \IntlDateFormatter($locale, (int)$format, (int)$format);
         } else {
@@ -82,10 +86,14 @@ public function strftime(string $format, int|string|\DateTimeInterface|null $tim
 
         if (empty($locale)) {
             // get current locale
-            $locale = setlocale(LC_TIME, '0');
+            $locale = (string)setlocale(LC_TIME, '0');
         } else {
             $locale = (string)$locale;
         }
+        // Use fallback locale if 'C' is provided.
+        if ($locale === 'C') {
+            $locale = 'en-US';
+        }
         // remove trailing part not supported by ext-intl locale
         $locale = preg_replace('/[^\w-].*$/', '', $locale);
 

typo3/sysext/core/Tests/Unit/Localization/DateFormatterTest.php

@@ -30,32 +30,67 @@ public static function formatDateProvider(): \Generator
             "yyyy.MM.dd G 'at' HH:mm:ss zzz",
         ];
         yield 'full - no locale' => [
-            'Thursday, February 2, 2023 at 13:05:00 Coordinated Universal Time',
+            'Thursday, February 2, 2023 at 1:05:00 PM Coordinated Universal Time',
+            'FULL',
+        ];
+        yield 'full - locale C' => [
+            'Thursday, February 2, 2023 at 1:05:00 PM Coordinated Universal Time',
             'FULL',
+            new Locale('C'),
         ];
         yield 'long - no locale' => [
-            'February 2, 2023 at 13:05:00 UTC',
+            'February 2, 2023 at 1:05:00 PM UTC',
+            'LONG',
+        ];
+        yield 'long - locale C' => [
+            'February 2, 2023 at 1:05:00 PM UTC',
             'LONG',
+            new Locale('C'),
         ];
         yield 'medium - no locale' => [
-            'Feb 2, 2023, 13:05:00',
+            'Feb 2, 2023, 1:05:00 PM',
             'MEDIUM',
         ];
+        yield 'medium - locale C' => [
+            'Feb 2, 2023, 1:05:00 PM',
+            'MEDIUM',
+            new Locale('C'),
+        ];
         yield 'medium with int - no locale' => [
-            'Feb 2, 2023, 13:05:00',
+            'Feb 2, 2023, 1:05:00 PM',
+            \IntlDateFormatter::MEDIUM,
+        ];
+        yield 'medium with int - locale C' => [
+            'Feb 2, 2023, 1:05:00 PM',
             \IntlDateFormatter::MEDIUM,
+            new Locale('C'),
         ];
         yield 'medium with int as string - no locale' => [
-            'Feb 2, 2023, 13:05:00',
+            'Feb 2, 2023, 1:05:00 PM',
             (string)\IntlDateFormatter::MEDIUM,
         ];
+        yield 'medium with int as string - locale C' => [
+            'Feb 2, 2023, 1:05:00 PM',
+            (string)\IntlDateFormatter::MEDIUM,
+            new Locale('C'),
+        ];
         yield 'short - no locale' => [
-            '2/2/23, 13:05',
+            '2/2/23, 1:05 PM',
             'SHORT',
         ];
+        yield 'short - locale C' => [
+            '2/2/23, 1:05 PM',
+            'SHORT',
+            new Locale('C'),
+        ];
         yield 'short in lowercase - no locale' => [
-            '2/2/23, 13:05',
+            '2/2/23, 1:05 PM',
+            'short',
+        ];
+        yield 'short in lowercase - locale C' => [
+            '2/2/23, 1:05 PM',
             'short',
+            new Locale('C'),
         ];
         yield 'regular formatting - en-US locale' => [
             '2023.02.02 AD at 13:05:00 UTC',