events: Fix bug in get_recent_conversations_recipient_id.

user_profile.id was confused for user_profile.recipient_id. These bugs
are particularly sneaky as they can go undetected by tests due to ids of
objects accidentally coinciding. We add a mitigation for this class of
mistakes by shifting the Recipient.id sequence in test db.

This was introduced in dda3ff41e1.
On the rare occasion where user_profile.id would coincide with
recipient_id passed to the function, we would return the wrong value.
That is, instead of correctly returning recipient_id, we would return
sender.recipient_id - recipient id of the sender of the message, thus
possibly returning user_profile.recipient_id (if user_profile is the
sender) - exactly the situation the function wanted to avoid
with the `if recipient_id == my_recipient_id:` if. Ultimately resulting
in incorrect/malformed data in
state['raw_recent_private_conversations'].

zerver/lib/message.py

@@ -1160,7 +1160,7 @@ def get_recent_conversations_recipient_id(user_profile: UserProfile,
     get_recent_private_conversations would have used to record that
     message in its data structure.
     """
-    my_recipient_id = user_profile.id
+    my_recipient_id = user_profile.recipient_id
     if recipient_id == my_recipient_id:
         return UserProfile.objects.values_list('recipient_id', flat=True).get(id=sender_id)
     return recipient_id

zilencer/management/commands/populate_db.py

@@ -11,6 +11,7 @@ from django.conf import settings
 from django.contrib.sessions.models import Session
 from django.core.management import call_command
 from django.core.management.base import BaseCommand, CommandParser
+from django.db import connection
 from django.db.models import F, Max
 from django.utils.timezone import now as timezone_now
 from django.utils.timezone import timedelta as timezone_timedelta
@@ -252,6 +253,15 @@ class Command(BaseCommand):
         if options["test_suite"]:
             random.seed(0)
 
+            with connection.cursor() as cursor:
+                # Sometimes bugs relating to confusing recipient.id for recipient.type_id
+                # or <object>.id for <object>.recipient_id remain undiscovered by the test suite
+                # due to these numbers happening to coincide in such a way that it makes tests
+                # accidentally pass. By bumping the Recipient.id sequence by a large enough number,
+                # we can have those ids in a completely different range of values than object ids,
+                # eliminatng the possibility of such coincidences.
+                cursor.execute("SELECT setval('zerver_recipient_id_seq', 100)")
+
         # If max_topics is not set, we set it proportional to the
         # number of messages.
         if options["max_topics"] is None: