Move to timezone aware datetimes (#1895)

* Move to timezone aware datetimes

With the shift of the discord.py library to timezone aware datetimes, this commit changes datetimes throughout the bot to be in the UTC timezone accordingly.

This has several advantages:
- There's no need to discard the TZ every time the datetime of a Discord object is fetched.
- Using TZ aware datetimes reduces the likelihood of silently adding bugs into the codebase (can't compare an aware datetime with a naive one).
- Our DB already stores datetimes in UTC, but we've been discarding the TZ so far whenever we read from it.

Specific places in the codebase continue using naive datetimes, mainly for UI purposes (for examples embed footers use naive datetimes to display local time).

* Improve ISODateTime converter documentation

Co-authored-by: Kieran Siek <[email protected]>

2 files changed, 41 insertions, 36 deletions

diff --git a/tests/bot/test_converters.py b/tests/bot/test_converters.py
index ef6c8e19e..988b3857b 100644
--- a/tests/bot/test_converters.py
+++ b/tests/bot/test_converters.py
@@ -1,6 +1,6 @@
-import datetime
 import re
 import unittest
+from datetime import MAXYEAR, datetime, timezone
 from unittest.mock import MagicMock, patch
 
 from dateutil.relativedelta import relativedelta
@@ -17,7 +17,7 @@ class ConverterTests(unittest.IsolatedAsyncioTestCase):
         cls.context = MagicMock
         cls.context.author = 'bob'
 
-        cls.fixed_utc_now = datetime.datetime.fromisoformat('2019-01-01T00:00:00')
+        cls.fixed_utc_now = datetime.fromisoformat('2019-01-01T00:00:00+00:00')
 
     async def test_tag_name_converter_for_invalid(self):
         """TagNameConverter should raise the correct exception for invalid tag names."""
@@ -111,7 +111,7 @@ class ConverterTests(unittest.IsolatedAsyncioTestCase):
             expected_datetime = self.fixed_utc_now + relativedelta(**duration_dict)
 
             with patch('bot.converters.datetime') as mock_datetime:
-                mock_datetime.utcnow.return_value = self.fixed_utc_now
+                mock_datetime.now.return_value = self.fixed_utc_now
 
                 with self.subTest(duration=duration, duration_dict=duration_dict):
                     converted_datetime = await converter.convert(self.context, duration)
@@ -157,52 +157,53 @@ class ConverterTests(unittest.IsolatedAsyncioTestCase):
     async def test_duration_converter_out_of_range(self, mock_datetime):
         """Duration converter should raise BadArgument if datetime raises a ValueError."""
         mock_datetime.__add__.side_effect = ValueError
-        mock_datetime.utcnow.return_value = mock_datetime
+        mock_datetime.now.return_value = mock_datetime
 
-        duration = f"{datetime.MAXYEAR}y"
+        duration = f"{MAXYEAR}y"
         exception_message = f"`{duration}` results in a datetime outside the supported range."
         with self.assertRaisesRegex(BadArgument, re.escape(exception_message)):
             await Duration().convert(self.context, duration)
 
     async def test_isodatetime_converter_for_valid(self):
         """ISODateTime converter returns correct datetime for valid datetime string."""
+        utc = timezone.utc
         test_values = (
             # `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)),
+            ('2019-09-02T02:03:05Z', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
+            ('2019-09-02 02:03:05Z', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
 
             # `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)),
+            ('2019-09-02T03:18:05+01:15', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
+            ('2019-09-02 03:18:05+01:15', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
+            ('2019-09-02T00:48:05-01:15', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
+            ('2019-09-02 00:48:05-01:15', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
 
             # `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)),
+            ('2019-09-02T03:18:05+0115', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
+            ('2019-09-02 03:18:05+0115', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
+            ('2019-09-02T00:48:05-0115', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
+            ('2019-09-02 00:48:05-0115', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
 
             # `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)),
+            ('2019-09-02 03:03:05+01', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
+            ('2019-09-02T01:03:05-01', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
 
             # `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)),
+            ('2019-09-02T02:03:05', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
+            ('2019-09-02 02:03:05', datetime(2019, 9, 2, 2, 3, 5, tzinfo=utc)),
 
             # `YYYY-mm-ddTHH:MM` | `YYYY-mm-dd HH:MM`
-            ('2019-11-12T09:15', datetime.datetime(2019, 11, 12, 9, 15)),
-            ('2019-11-12 09:15', datetime.datetime(2019, 11, 12, 9, 15)),
+            ('2019-11-12T09:15', datetime(2019, 11, 12, 9, 15, tzinfo=utc)),
+            ('2019-11-12 09:15', datetime(2019, 11, 12, 9, 15, tzinfo=utc)),
 
             # `YYYY-mm-dd`
-            ('2019-04-01', datetime.datetime(2019, 4, 1)),
+            ('2019-04-01', datetime(2019, 4, 1, tzinfo=utc)),
 
             # `YYYY-mm`
-            ('2019-02-01', datetime.datetime(2019, 2, 1)),
+            ('2019-02-01', datetime(2019, 2, 1, tzinfo=utc)),
 
             # `YYYY`
-            ('2025', datetime.datetime(2025, 1, 1)),
+            ('2025', datetime(2025, 1, 1, tzinfo=utc)),
         )
 
         converter = ISODateTime()
@@ -210,7 +211,6 @@ class ConverterTests(unittest.IsolatedAsyncioTestCase):
         for datetime_string, expected_dt in test_values:
             with self.subTest(datetime_string=datetime_string, expected_dt=expected_dt):
                 converted_dt = await converter.convert(self.context, datetime_string)
-                self.assertIsNone(converted_dt.tzinfo)
                 self.assertEqual(converted_dt, expected_dt)
 
     async def test_isodatetime_converter_for_invalid(self):
diff --git a/tests/bot/utils/test_time.py b/tests/bot/utils/test_time.py
index 8edffd1c9..a3dcbfc0a 100644
--- a/tests/bot/utils/test_time.py
+++ b/tests/bot/utils/test_time.py
@@ -72,9 +72,9 @@ class TimeTests(unittest.TestCase):
     def test_format_infraction_with_duration_custom_units(self):
         """format_infraction_with_duration should work for custom max_units."""
         test_cases = (
-            ('3000-12-12T00:01:00Z', datetime(3000, 12, 11, 12, 5, 5), 6,
+            ('3000-12-12T00:01:00Z', datetime(3000, 12, 11, 12, 5, 5, tzinfo=timezone.utc), 6,
              '<t:32533488060:f> (11 hours, 55 minutes and 55 seconds)'),
-            ('3000-11-23T20:09:00Z', datetime(3000, 4, 25, 20, 15), 20,
+            ('3000-11-23T20:09:00Z', datetime(3000, 4, 25, 20, 15, tzinfo=timezone.utc), 20,
              '<t:32531918940:f> (6 months, 28 days, 23 hours and 54 minutes)')
         )
 
@@ -84,16 +84,21 @@ class TimeTests(unittest.TestCase):
 
     def test_format_infraction_with_duration_normal_usage(self):
         """format_infraction_with_duration should work for normal usage, across various durations."""
+        utc = timezone.utc
         test_cases = (
-            ('2019-12-12T00:01:00Z', datetime(2019, 12, 11, 12, 0, 5), 2, '<t:1576108860:f> (12 hours and 55 seconds)'),
-            ('2019-12-12T00:01:00Z', datetime(2019, 12, 11, 12, 0, 5), 1, '<t:1576108860:f> (12 hours)'),
-            ('2019-12-12T00:00:00Z', datetime(2019, 12, 11, 23, 59), 2, '<t:1576108800:f> (1 minute)'),
-            ('2019-11-23T20:09:00Z', datetime(2019, 11, 15, 20, 15), 2, '<t:1574539740:f> (7 days and 23 hours)'),
-            ('2019-11-23T20:09:00Z', datetime(2019, 4, 25, 20, 15), 2, '<t:1574539740:f> (6 months and 28 days)'),
-            ('2019-11-23T20:58:00Z', datetime(2019, 11, 23, 20, 53), 2, '<t:1574542680:f> (5 minutes)'),
-            ('2019-11-24T00:00:00Z', datetime(2019, 11, 23, 23, 59, 0), 2, '<t:1574553600:f> (1 minute)'),
-            ('2019-11-23T23:59:00Z', datetime(2017, 7, 21, 23, 0), 2, '<t:1574553540:f> (2 years and 4 months)'),
-            ('2019-11-23T23:59:00Z', datetime(2019, 11, 23, 23, 49, 5), 2,
+            ('2019-12-12T00:01:00Z', datetime(2019, 12, 11, 12, 0, 5, tzinfo=utc), 2,
+                '<t:1576108860:f> (12 hours and 55 seconds)'),
+            ('2019-12-12T00:01:00Z', datetime(2019, 12, 11, 12, 0, 5, tzinfo=utc), 1, '<t:1576108860:f> (12 hours)'),
+            ('2019-12-12T00:00:00Z', datetime(2019, 12, 11, 23, 59, tzinfo=utc), 2, '<t:1576108800:f> (1 minute)'),
+            ('2019-11-23T20:09:00Z', datetime(2019, 11, 15, 20, 15, tzinfo=utc), 2,
+                '<t:1574539740:f> (7 days and 23 hours)'),
+            ('2019-11-23T20:09:00Z', datetime(2019, 4, 25, 20, 15, tzinfo=utc), 2,
+                '<t:1574539740:f> (6 months and 28 days)'),
+            ('2019-11-23T20:58:00Z', datetime(2019, 11, 23, 20, 53, tzinfo=utc), 2, '<t:1574542680:f> (5 minutes)'),
+            ('2019-11-24T00:00:00Z', datetime(2019, 11, 23, 23, 59, 0, tzinfo=utc), 2, '<t:1574553600:f> (1 minute)'),
+            ('2019-11-23T23:59:00Z', datetime(2017, 7, 21, 23, 0, tzinfo=utc), 2,
+             '<t:1574553540:f> (2 years and 4 months)'),
+            ('2019-11-23T23:59:00Z', datetime(2019, 11, 23, 23, 49, 5, tzinfo=utc), 2,
              '<t:1574553540:f> (9 minutes and 55 seconds)'),
             (None, datetime(2019, 11, 23, 23, 49, 5), 2, None),
         )