home: Don't use pointer to compute furthest_read_time.

When a user is reading messages only in stream or topic narrows, the pointer
can be left far behind. Using this to compute the furthest_read_time causes
the banckruptcy banner to be shown even when a user has been actively
reading messages. This commit switches to using the sent time on the last
message that the user has read to compute the furthest read time.

zerver/models.py

@@ -1964,6 +1964,10 @@ def get_usermessage_by_message_id(user_profile: UserProfile, message_id: int) ->
     except UserMessage.DoesNotExist:
         return None
 
+def get_latest_read_usermessage(user_profile: UserProfile) -> Optional[UserMessage]:
+    return UserMessage.objects.select_related().filter(user_profile=user_profile,
+                                                       flags=UserMessage.flags.read).last()
+
 class ArchivedUserMessage(AbstractUserMessage):
     """Used as a temporary holding place for deleted UserMessages objects
     before they are permanently deleted.  This is an important part of

zerver/tests/test_home.py

@@ -22,7 +22,7 @@ from zerver.lib.users import compute_show_invites_and_add_streams
 from zerver.models import (
     get_realm, get_stream, get_user, UserProfile,
     flush_per_request_caches, DefaultStream, Realm,
-    get_system_bot,
+    get_system_bot, UserMessage
 )
 from zerver.views.home import sent_time_in_epoch_seconds, compute_navbar_logo_url
 from corporate.models import Customer, CustomerPlan
@@ -458,9 +458,19 @@ class HomeTest(ZulipTestCase):
         user_profile.save()
 
         self.login_user(user_profile)
-        with patch('logging.warning') as mock:
-            result = self._get_home_page()
-        mock.assert_called_once_with('User %s has invalid pointer 999999' % (user_profile.id,))
+        result = self._get_home_page()
+        self._sanity_check(result)
+
+    def test_no_read_user_messages(self) -> None:
+        user_profile = self.example_user('hamlet')
+        user_profile.pointer = 1
+        user_profile.save()
+
+        # Mark all messages as unread
+        UserMessage.objects.filter(user_profile=user_profile).update(flags=~UserMessage.flags.read)
+
+        self.login_user(user_profile)
+        result = self._get_home_page()
         self._sanity_check(result)
 
     def test_topic_narrow(self) -> None:

zerver/views/home.py

@@ -13,7 +13,7 @@ from zerver.forms import ToSForm
 from zerver.models import Message, Stream, UserProfile, \
     Realm, UserMessage, \
     PreregistrationUser, \
-    get_usermessage_by_message_id
+    get_latest_read_usermessage
 from zerver.lib.events import do_events_register
 from zerver.lib.actions import do_change_tos_version, \
     realm_user_count
@@ -223,10 +223,7 @@ def home_real(request: HttpRequest) -> HttpResponse:
             register_ret['pointer'] = register_ret['max_message_id']
         furthest_read_time = None
     else:
-        latest_read = get_usermessage_by_message_id(user_profile, user_profile.pointer)
-        if latest_read is None:
-            # Don't completely fail if your saved pointer ID is invalid
-            logging.warning("User %s has invalid pointer %s" % (user_profile.id, user_profile.pointer))
+        latest_read = get_latest_read_usermessage(user_profile)
         furthest_read_time = sent_time_in_epoch_seconds(latest_read)
 
     # We pick a language for the user as follows: