Display document expiration in UTC

The document expiration mail displays the date of the upcoming document expiration, but different timezones makes that date ambituous.  Instead, clearly show that as a timestamp in UTC.

Fixes ietf-tools#1825

ietf/doc/expire.py

@@ -8,6 +8,7 @@
 
 import datetime, os, shutil, glob, re
 from pathlib import Path
+from zoneinfo import ZoneInfo
 
 from typing import List, Optional      # pyflakes:ignore
 
@@ -86,10 +87,15 @@ def send_expire_warning_for_draft(doc):
         (doc.get_state_slug("draft") != "active")):
         return # don't warn about dead or inactive documents
 
-    expiration = doc.expires.astimezone(DEADLINE_TZINFO).date()
+    expiration = doc.expires.astimezone(
+        DEADLINE_TZINFO
+    ).replace(
+        hour=0, minute=0, second=0, microsecond=0
+    ).astimezone(
+        ZoneInfo('UTC')
+    )
     now_plus_12hours = timezone.now() + datetime.timedelta(hours=12)
-    soon = now_plus_12hours.date()
-    if expiration <= soon:
+    if expiration <= now_plus_12hours:
         # The document will expire very soon, which will send email to the
         # same people, so do not send the warning at this point in time
         return

ietf/doc/tests_draft.py

@@ -711,6 +711,7 @@ def test_warn_expirable_drafts(self):
         self.assertTrue('draft-ietf-mars-test@' in outbox[-1]['To']) # Gets the authors
         self.assertTrue('[email protected]' in outbox[-1]['Cc'])
         self.assertTrue('aread@' in outbox[-1]['Cc'])
+        self.assertIn('UTC' , get_payload_text(outbox[-1]))
 
         # hack into expirable state to expire in 10 hours
         draft.expires = timezone.now() + datetime.timedelta(hours=10)

ietf/templates/doc/draft/expire_warning_email.txt

@@ -1,7 +1,7 @@
-{% load ietf_filters %}{% autoescape off %}The following Internet-Draft will expire soon:
+{% load ietf_filters tz %}{% autoescape off %}The following Internet-Draft will expire soon:
 
 Name:     {{ doc.name|clean_whitespace }}
 Title:    {{ doc.title}}
 State:    {{ state }}
-Expires:  {{ expiration }} (in {{ expiration|timeuntil }})
+Expires:  {{ expiration|utc }} (in {{ expiration|timeuntil }})
 {% endautoescape %}