Make ISODateTime return tz-unaware datetime

The parser we use, `dateutil.parsers.isoparse` returns a timezone-
aware or timezone-unaware `datetime` object depending on whether or
not the datetime string included a timezone offset specification.

Since we can't compare tz-aware objects to tz-unaware objects it's
better to make sure our converter is consistent in the type it will
return.

For now, I've chosen to return tz-unaware datetime objects, since
`discord.py` also returns tz-unaware datetime objects when accessing
datetime-related attributes of objects. Since we're likely to compare
"our" datetime objects to discord.py-provided datetime objects, I
think that's the most parsimonious option for now.

Note: It's probably a good idea to open a larger discussion about
using timezone-aware datetime objects throughout the library to
avoid a UTC-time being interpreted as localtime. This will require
a broader discussion than this commit/PR allows, though.

2 files changed, 33 insertions, 1 deletions

diff --git a/bot/converters.py b/bot/converters.py
index 59a6f6b07..27223e632 100644
--- a/bot/converters.py
+++ b/bot/converters.py
@@ -5,6 +5,7 @@ from ssl import CertificateError
 from typing import Union
 
 import dateutil.parser
+import dateutil.tz
 import discord
 from aiohttp import ClientConnectorError
 from dateutil.relativedelta import relativedelta
@@ -227,12 +228,18 @@ class ISODateTime(Converter):
 
         The converter is flexible in the formats it accepts, as it uses the `isoparse` method of
         `dateutil.parser`. In general, it accepts datetime strings that start with a date,
-        optionally followed by a time.
+        optionally followed by a time. Specifying a timezone offset in the datetime string is
+        supported, but the `datetime` object will be converted to UTC and will be returned without
+        `tzinfo` as a timezone-unaware `datetime` object.
 
         See: https://dateutil.readthedocs.io/en/stable/parser.html#dateutil.parser.isoparse
 
         Formats that are guaranteed to be valid by our tests are:
 
+        - `YYYY-mm-ddTHH:MM:SSZ` | `YYYY-mm-dd HH:MM:SSZ`
+        - `YYYY-mm-ddTHH:MM:SS±HH:MM` | `YYYY-mm-dd HH:MM:SS±HH:MM`
+        - `YYYY-mm-ddTHH:MM:SS±HHMM` | `YYYY-mm-dd HH:MM:SS±HHMM`
+        - `YYYY-mm-ddTHH:MM:SS±HH` | `YYYY-mm-dd HH:MM:SS±HH`
         - `YYYY-mm-ddTHH:MM:SS` | `YYYY-mm-dd HH:MM:SS`
         - `YYYY-mm-ddTHH:MM` | `YYYY-mm-dd HH:MM`
         - `YYYY-mm-dd`
@@ -247,4 +254,8 @@ class ISODateTime(Converter):
         except ValueError:
             raise BadArgument(f"`{datetime_string}` is not a valid ISO-8601 datetime string")
 
+        if dt.tzinfo:
+            dt = dt.astimezone(dateutil.tz.UTC)
+            dt = dt.replace(tzinfo=None)
+
         return dt
diff --git a/tests/test_converters.py b/tests/test_converters.py
index 8093f55ac..86e8f2249 100644
--- a/tests/test_converters.py
+++ b/tests/test_converters.py
@@ -190,6 +190,27 @@ def test_duration_converter_for_invalid(duration: str):
 @pytest.mark.parametrize(
     ("datetime_string", "expected_dt"),
     (
+
+        # `YYYY-mm-ddTHH:MM:SSZ` | `YYYY-mm-dd HH:MM:SSZ`
+        ('2019-09-02T02:03:05Z', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+        ('2019-09-02 02:03:05Z', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+
+        # `YYYY-mm-ddTHH:MM:SS±HH:MM` | `YYYY-mm-dd HH:MM:SS±HH:MM`
+        ('2019-09-02T03:18:05+01:15', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+        ('2019-09-02 03:18:05+01:15', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+        ('2019-09-02T00:48:05-01:15', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+        ('2019-09-02 00:48:05-01:15', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+
+        # `YYYY-mm-ddTHH:MM:SS±HHMM` | `YYYY-mm-dd HH:MM:SS±HHMM`
+        ('2019-09-02T03:18:05+0115', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+        ('2019-09-02 03:18:05+0115', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+        ('2019-09-02T00:48:05-0115', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+        ('2019-09-02 00:48:05-0115', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+
+        # `YYYY-mm-ddTHH:MM:SS±HH` | `YYYY-mm-dd HH:MM:SS±HH`
+        ('2019-09-02 03:03:05+01', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+        ('2019-09-02T01:03:05-01', datetime.datetime(2019, 9, 2, 2, 3, 5)),
+
         # `YYYY-mm-ddTHH:MM:SS` | `YYYY-mm-dd HH:MM:SS`
         ('2019-09-02T02:03:05', datetime.datetime(2019, 9, 2, 2, 3, 5)),
         ('2019-09-02 02:03:05', datetime.datetime(2019, 9, 2, 2, 3, 5)),