chore: enforce USE_TZ setting expectations in migrations (ietf-tools#4386)

* chore: enforce USE_TZ setting expectations in migrations

* chore: keep USE_TZ=False until changed manually

Author: jennifer-richards

ietf/settings.py

@@ -114,7 +114,7 @@
 # to load the internationalization machinery.
 USE_I18N = False
 
-USE_TZ = True
+USE_TZ = False
 
 if SERVER_MODE == 'production':
     MEDIA_ROOT = '/a/www/www6s/lib/dt/media/'

ietf/utils/migrations/0002_convert_timestamps_to_utc.py

@@ -1,4 +1,8 @@
 # Generated by Django 2.2.28 on 2022-06-21 11:44
+#
+# Important: To avoid corrupting timestamps in the database, do not use this migration as a dependency for
+# future migrations. Use 0003_pause_to_change_use_tz instead.
+#
 
 from django.conf import settings
 from django.db import migrations, connection
@@ -107,6 +111,10 @@
 
 
 def forward(apps, schema_editor):
+    # Check that the USE_TZ has been False so far, otherwise we might be corrupting timestamps. If this test
+    # fails, be sure that no timestamps have been set since changing USE_TZ to True before re-running!
+    assert not getattr(settings, 'USE_TZ', False), 'must keep USE_TZ = False until after this migration'
+
     # Check that we can safely ignore celery beat columns - it defaults to UTC if CELERY_TIMEZONE is not set.
     celery_timezone = getattr(settings, 'CELERY_TIMEZONE', None)
     assert celery_timezone in ('UTC', None), 'update migration, celery is not using UTC'

ietf/utils/migrations/0003_pause_to_change_use_tz.py

@@ -0,0 +1,23 @@
+# Generated by Django 2.2.28 on 2022-08-29 10:16
+
+from django.conf import settings
+from django.db import migrations
+
+
+def forward(apps, schema_editor):
+    assert getattr(settings, 'USE_TZ', False), 'Please change USE_TZ to True before continuing.'
+
+
+def reverse(apps, schema_editor):
+    assert not getattr(settings, 'USE_TZ', False), 'Please change USE_TZ to False before continuing.'
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('utils', '0002_convert_timestamps_to_utc'),
+    ]
+
+    operations = [
+        migrations.RunPython(forward, reverse),
+    ]