refactor: Extract get_user_info_for_message_updates.

We'll want to expand this to get users that were mentioned in
the prior message, but this commit is just a refactoring.

zerver/lib/actions.py

@@ -3001,6 +3001,28 @@ def truncate_topic(topic):
     # type: (Text) -> Text
     return truncate_content(topic, MAX_SUBJECT_LENGTH, "...")
 
+MessageUpdateUserInfoResult = TypedDict('MessageUpdateUserInfoResult', {
+    'message_user_ids': Set[int],
+})
+
+def get_user_info_for_message_updates(message_id):
+    # type: (int) -> MessageUpdateUserInfoResult
+
+    # 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,
+    # mentions and similar rendering features.  This may be a
+    # decision we change in the future.
+    query = UserMessage.objects.filter(
+        message=message_id,
+        flags=~UserMessage.flags.historical
+    )
+
+    message_user_ids = set(query.values_list('user_profile_id', flat=True))
+
+    return dict(
+        message_user_ids=message_user_ids,
+    )
 
 def update_user_message_flags(message, ums):
     # type: (Message, Iterable[UserMessage]) -> None

zerver/tests/test_messages.py

@@ -16,6 +16,7 @@ from zerver.lib.addressee import Addressee
 from zerver.lib.actions import (
     do_send_messages,
     get_userids_for_missed_messages,
+    get_user_info_for_message_updates,
     internal_send_private_message,
 )
 
@@ -1499,6 +1500,23 @@ class EditMessageTest(ZulipTestCase):
                          ('<p>content before edit, line 1</p>\n'
                           '<p>content before edit, line 3</p>'))
 
+    def test_user_info_for_updates(self):
+        # type: () -> None
+        hamlet = self.example_user('hamlet')
+        cordelia = self.example_user('cordelia')
+
+        self.login(hamlet.email)
+        self.subscribe(hamlet, 'Scotland')
+        self.subscribe(cordelia, 'Scotland')
+
+        msg_id = self.send_message(hamlet.email, 'Scotland', Recipient.STREAM,
+                                   subject='subject 1', content='content 1')
+
+        user_info = get_user_info_for_message_updates(msg_id)
+        message_user_ids = user_info['message_user_ids']
+        self.assertIn(hamlet.id, message_user_ids)
+        self.assertIn(cordelia.id, message_user_ids)
+
     def test_edit_cases(self):
         # type: () -> None
         """This test verifies the accuracy of construction of Zulip's edit

zerver/views/messages.py

@@ -19,7 +19,7 @@ from zerver.lib.actions import recipient_for_emails, do_update_message_flags, \
     compute_mit_user_fullname, compute_irc_user_fullname, compute_jabber_user_fullname, \
     create_mirror_user_if_needed, check_send_message, do_update_message, \
     extract_recipients, truncate_body, render_incoming_message, do_delete_message, \
-    do_mark_all_as_read, do_mark_stream_messages_as_read
+    do_mark_all_as_read, do_mark_stream_messages_as_read, get_user_info_for_message_updates
 from zerver.lib.queue import queue_json_publish
 from zerver.lib.cache import (
     generic_bulk_cached_fetch,
@@ -1094,17 +1094,7 @@ def update_message_backend(request, user_profile,
             content = "(deleted)"
         content = truncate_body(content)
 
-        # 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,
-        # mentions and similar rendering features.  This may be a
-        # decision we change in the future.
-        query = UserMessage.objects.filter(
-            message=message.id,
-            flags=~UserMessage.flags.historical
-        )
-
-        message_user_ids = set(query.values_list('user_profile_id', flat=True))
+        user_info = get_user_info_for_message_updates(message.id)
 
         # We render the message using the current user's realm; since
         # the cross-realm bots never edit messages, this should be
@@ -1112,7 +1102,7 @@ def update_message_backend(request, user_profile,
         # Note: If rendering fails, the called code will raise a JsonableError.
         rendered_content = render_incoming_message(message,
                                                    content,
-                                                   message_user_ids,
+                                                   user_info['message_user_ids'],
                                                    user_profile.realm)
         links_for_embed |= message.links_for_preview