The reverse transformation ignores text without time because time zones influences just time. If you are inputting a date, you wouldn't like that to be changed because the system is implying 00:00:00 and that means the previous day in a latter timezone.

Maybe the behavior is not perfect, but that stems from the fact that PHP doesn't have a \Date type, so we are forced to set a time somewhere; but if we changed it, it would fail otherwise with this example:

    public function testReverseTransformDateWithoutTime()
    {
        $transformer = new DateTimeToLocalizedStringTransformer(
            'UTC',
            'America/Louisville',
            \IntlDateFormatter::FULL,
            \IntlDateFormatter::FULL,
            \IntlDateFormatter::GREGORIAN,
            'yyyy-MM-dd'
        );

        $date = new \DateTime('2015-01-01T05:00:00+00:00');
        $this->assertEquals(
            $date->format('Y-m-d'),
            $transformer->reverseTransform('2015-01-01')->format('Y-m-d')
        );
    }

..which is the "normal" behavior of a programmer: using implied timezone (which probably isn't UTC).

This problem seems to be caused by IntlDateFormatter stubs.
In my env, a generated timestamp completely differs between stubs and native. A former one seems to not deal with the timezone something properly.

/cc @webmozart @HeahDude

@issei-m this issue should have been fixed in #21218 as of 2.7.23, 2.8.16, 3.1.9, 3.2.2, could you please confirm?

Damn, this reverses a previous PR where I was involved. I understand why is that like that, but now I'm just desiring so bad a \Date object in PHP...

@HeahDude I don't think so. As before I said, this problem doesn't seem to be DateTimeToLocalizedStringTransformer's matter. This problem is caused by \Symfony\Component\Intl\DateFormatter\IntlDateFormatter in Intl component. (So you wouldn't encounter if you're using a native one)

See following snippet - the POC for my opinion on my env (PHP 7.0):

date_default_timezone_set('Asia/Tokyo'); // My timezone.

$pattern = 'yyyy-MM-dd';

$nativeIntlDf = new \IntlDateFormatter('en', \IntlDateFormatter::FULL, \IntlDateFormatter::FULL, 'UTC', \IntlDateFormatter::GREGORIAN, $pattern);
$polyfillIntlDf = new \Symfony\Component\Intl\DateFormatter\IntlDateFormatter('en', \IntlDateFormatter::FULL, \IntlDateFormatter::FULL, 'UTC', \IntlDateFormatter::GREGORIAN, $pattern);

var_dump(
    $nativeIntlDf->parse('2017-01-01'),  // 1483228800
    $polyfillIntlDf->parse('2017-01-01') // 1483196400
);

• A former one (1483228800) is care about a timezone well - it's 2017/01/01 00:00:00 in UTC
• But a latter one (1483196400) doesn't - it's 2016-12-31 15:00:00 in UTC (In other words, it's influenced by the current timezone)

This timestamp is passed to gmdate('Y-m-d') at here, eventually the result of a latter one is DateTime('2016-12-31 00:00:00', 'UTC').
As you can see, although this datetime object is set specific TZ after this, the final date would end up with wrong.

So we have to fix \Symfony\Component\Intl\DateFormatter\IntlDateFormatter, at least as well as native works IMHO.

Regards.

I've just opened a new issue about this problem.

Ok, thanks! Let's close here then as the original issue is about the transformer and has been fixed by #21218.