messages: Add unread 1:1/self DMs to pm_dict if DM group exists.

In get_raw_unread_data, 1:1 or self messages are added to pm_dict.
However, if a DirectMessageGroup is the recipient, the message is
added to huddle_dict by default.

To keep API compatibility, we override this behavior to populate
pm_dict for 1:1 and self DMs when a DirectMessageGroup exists.
This ensures clients relying on pm_dict continue to work during
and after the migration.

This PR fixes part of issue #25713.

zerver/lib/message.py

@@ -1007,9 +1007,26 @@ def extract_unread_data_from_um_rows(
 
         elif msg_type == Recipient.DIRECT_MESSAGE_GROUP:
             user_ids_string = get_direct_message_group_users(recipient_id)
-            direct_message_group_dict[message_id] = dict(
-                user_ids_string=user_ids_string,
-            )
+            user_ids = [int(uid) for uid in user_ids_string.split(",")]
+
+            # For API compatibility, we populate pm_dict for 1:1 and self DMs
+            # so clients relying on pm_dict continue to work during the migration.
+            # We populate direct_message_group_dict for group size > 2.
+            if len(user_ids) <= 2:
+                if len(user_ids) == 1:
+                    # For self-DM, other_user_id is the user's own id
+                    other_user_id = user_ids[0]
+                else:
+                    # For 1:1 DM, other_user_id is the other participant
+                    other_user_id = user_ids[1] if user_ids[0] == user_profile.id else user_ids[0]
+
+                pm_dict[message_id] = dict(
+                    other_user_id=other_user_id,
+                )
+            else:
+                direct_message_group_dict[message_id] = dict(
+                    user_ids_string=user_ids_string,
+                )
 
         # TODO: Add support for alert words here as well.
         is_mentioned = (row["flags"] & UserMessage.flags.mentioned) != 0

zerver/tests/test_message_flags.py

@@ -38,6 +38,7 @@ from zerver.models import (
 )
 from zerver.models.groups import NamedUserGroup
 from zerver.models.realms import get_realm
+from zerver.models.recipients import get_or_create_direct_message_group
 from zerver.models.streams import get_stream
 
 if TYPE_CHECKING:
@@ -1143,6 +1144,37 @@ class GetUnreadMsgsTest(ZulipTestCase):
             dict(other_user_id=cordelia.id),
         )
 
+    def test_raw_unread_personal_using_direct_group_message(self) -> None:
+        cordelia = self.example_user("cordelia")
+        othello = self.example_user("othello")
+        hamlet = self.example_user("hamlet")
+
+        # creating direct message group for 1:1 messages
+        get_or_create_direct_message_group(id_list=[cordelia.id, hamlet.id])
+        get_or_create_direct_message_group(id_list=[othello.id, hamlet.id])
+
+        cordelia_pm_message_ids = [self.send_personal_message(cordelia, hamlet) for i in range(3)]
+        othello_pm_message_ids = [self.send_personal_message(othello, hamlet) for i in range(3)]
+
+        raw_unread_data = get_raw_unread_data(
+            user_profile=hamlet,
+        )
+        pm_dict = raw_unread_data["pm_dict"]
+
+        self.assertEqual(
+            set(pm_dict.keys()),
+            set(cordelia_pm_message_ids) | set(othello_pm_message_ids),
+        )
+
+        self.assertEqual(
+            pm_dict[cordelia_pm_message_ids[0]],
+            dict(other_user_id=cordelia.id),
+        )
+        self.assertEqual(
+            pm_dict[othello_pm_message_ids[0]],
+            dict(other_user_id=othello.id),
+        )
+
     def test_raw_unread_personal_from_self(self) -> None:
         hamlet = self.example_user("hamlet")
 
@@ -1237,6 +1269,39 @@ class GetUnreadMsgsTest(ZulipTestCase):
             dict(other_user_id=hamlet.id),
         )
 
+    def test_raw_unread_personal_from_self_using_direct_message_group(self) -> None:
+        hamlet = self.example_user("hamlet")
+
+        # creating direct message group for self messages
+        get_or_create_direct_message_group(id_list=[hamlet.id])
+
+        # Send a message to ourself.
+        message_id = self.send_personal_message(
+            from_user=hamlet,
+            to_user=hamlet,
+            read_by_sender=False,
+        )
+
+        um = UserMessage.objects.get(
+            user_profile_id=hamlet.id,
+            message_id=message_id,
+        )
+        self.assertFalse(um.flags.read)
+
+        raw_unread_data = get_raw_unread_data(
+            user_profile=hamlet,
+        )
+        pm_dict = raw_unread_data["pm_dict"]
+
+        self.assertEqual(
+            set(pm_dict.keys()),
+            {message_id},
+        )
+        self.assertEqual(
+            pm_dict[message_id],
+            dict(other_user_id=hamlet.id),
+        )
+
     def test_unread_msgs(self) -> None:
         sender = self.example_user("cordelia")
         sender_id = sender.id