prior_mention_user_ids: Exclude user who no longer has message access.

This commit updates the 'get_mentions_for_message_updates' function to
use the generic 'event_recipient_ids_for_action_on_messages' function
to determine users having access to the message and perform an
intersection with the mentioned users to filter out the users who
no longer can access the message.

It helps to add hardening such that if the invariant "no usermessage
row corresponding to a message exists if the user loses access to the
message" is violated due to some bug, it has minimal user impact.

zerver/actions/message_edit.py

@@ -310,7 +310,7 @@ def send_message_moved_breadcrumbs(
             )
 
 
-def get_mentions_for_message_updates(message_id: int) -> set[int]:
+def get_mentions_for_message_updates(message: Message) -> set[int]:
     # We exclude UserMessage.flags.historical rows since those
     # users did not receive the message originally, and thus
     # probably are not relevant for reprocessed alert_words,
@@ -318,7 +318,7 @@ def get_mentions_for_message_updates(message_id: int) -> set[int]:
     # decision we change in the future.
     mentioned_user_ids = (
         UserMessage.objects.filter(
-            message=message_id,
+            message=message.id,
             flags=~UserMessage.flags.historical,
         )
         .filter(
@@ -331,7 +331,10 @@ def get_mentions_for_message_updates(message_id: int) -> set[int]:
         )
         .values_list("user_profile_id", flat=True)
     )
-    return set(mentioned_user_ids)
+
+    user_ids_having_message_access = event_recipient_ids_for_action_on_messages([message])
+
+    return set(mentioned_user_ids) & user_ids_having_message_access
 
 
 def update_user_message_flags(
@@ -1410,7 +1413,7 @@ def check_update_message(
             content=message_edit_request.content,
             message_sender=message.sender,
         )
-        prior_mention_user_ids = get_mentions_for_message_updates(message.id)
+        prior_mention_user_ids = get_mentions_for_message_updates(message)
 
         # We render the message using the current user's realm; since
         # the cross-realm bots never edit messages, this should be

zerver/tests/test_message_edit.py

@@ -694,8 +694,9 @@ class EditMessageTest(ZulipTestCase):
         msg_id = self.send_stream_message(
             hamlet, "Denmark", content="@**Cordelia, Lear's daughter**"
         )
+        message = Message.objects.get(id=msg_id)
 
-        mention_user_ids = get_mentions_for_message_updates(msg_id)
+        mention_user_ids = get_mentions_for_message_updates(message)
         self.assertEqual(mention_user_ids, {cordelia.id})
 
     def test_edit_cases(self) -> None: