JSON encoder does not respect ZoneInfo (the IANA time zone database) when encoding datetime objects.

[agni-sairent]

Description

When using the JSON encoder on datetime objects with a timezone set using the IANA time zone database record, the encoder will not convert the datetime to UTC, only drop the timezone. This is not the case with the msgpack encoder, which correctly converts the datetime to UTC and removes the timezone.

I've replicated the issue using the Zone Info module from the Standard Library and the 3rd party module python-dateutil.

Minimal example:

import datetime
from zoneinfo import ZoneInfo

import msgspec

foo = datetime.datetime.now(tz=ZoneInfo("Europe/Prague"))
foo.isoformat()
# > 2023-08-24T12:17:59.327527+02:00

# NOT converted to UTC
foo_json = msgspec.json.decode(msgspec.json.encode(foo), type=datetime.datetime)
foo_json.isoformat()
# > 2023-08-24T12:17:59.327527+00:00

# Converted to UTC
foo_msgpack = msgspec.msgpack.decode(msgspec.msgpack.encode(foo), type=datetime.datetime)
foo_msgpack.isoformat()
# > 2023-08-24T10:17:59.327527+00:00

[jcrist]

Thanks for the excellent reproducible issue, this should be fixed by #534.