Symfony version(s) affected: 4.2.3

Description

PHP docs say:

The $timezone parameter and the current timezone are ignored when the $time parameter either is a UNIX timestamp (e.g. @946684800) or specifies a timezone (e.g. 2010-01-28T15:00:00+02:00).

This means the behaviour is different when the timezone is applied in the constructor or later with setTimezone.

If you specify the timezone when denormalizing, you'd expect all datetimes to come out in that timezone, regardless of (user) input. This currently does not happen.

How to reproduce

$normalizer = new \Symfony\Component\Serializer\Normalizer\DateTimeNormalizer(
    [
        \Symfony\Component\Serializer\Normalizer\DateTimeNormalizer::TIMEZONE_KEY => 'UTC'
    ]
);
$datetime = $normalizer->denormalize('2016-01-27T16:39:26+01:00', \DateTimeInterface::class);
// should be in UTC, but it's exactly the same as input, +01:00
var_dump($datetime->format(\DATE_RFC3339));

Possible Solution

When denormalizing, specify the timezone after having created the \DateTime instance, not in the constructor.

Additional context

• using in API Platform context means the datetime string is passed directly to this denormalizer, allowing the user to control the timezone of the created \DateTime instances