streams: Add notifications for description changes.

This is a part of #20289.

zerver/lib/actions.py

@@ -5116,7 +5116,39 @@ def do_rename_stream(stream: Stream, new_name: str, user_profile: UserProfile) -
     return {"email_address": new_email}
 
 
-def do_change_stream_description(stream: Stream, new_description: str) -> None:
+def send_change_stream_description_notification(
+    stream: Stream, *, old_description: str, new_description: str, acting_user: UserProfile
+) -> None:
+    sender = get_system_bot(settings.NOTIFICATION_BOT, acting_user.realm_id)
+    user_mention = silent_mention_syntax_for_user(acting_user)
+
+    with override_language(stream.realm.default_language):
+        notification_string = _(
+            "{user} changed the description for this stream.\n"
+            "Old description:\n"
+            "``` quote\n"
+            "{old_description}\n"
+            "```\n"
+            "New description:\n"
+            "``` quote\n"
+            "{new_description}\n"
+            "```"
+        )
+        notification_string = notification_string.format(
+            user=user_mention,
+            old_description=old_description,
+            new_description=new_description,
+        )
+
+        internal_send_stream_message(
+            sender, stream, Realm.STREAM_EVENTS_NOTIFICATION_TOPIC, notification_string
+        )
+
+
+def do_change_stream_description(
+    stream: Stream, new_description: str, *, acting_user: UserProfile
+) -> None:
+    old_description = stream.description
     stream.description = new_description
     stream.rendered_description = render_stream_description(new_description)
     stream.save(update_fields=["description", "rendered_description"])
@@ -5132,6 +5164,13 @@ def do_change_stream_description(stream: Stream, new_description: str) -> None:
     )
     send_event(stream.realm, event, can_access_stream_user_ids(stream))
 
+    send_change_stream_description_notification(
+        stream,
+        old_description=old_description,
+        new_description=new_description,
+        acting_user=acting_user,
+    )
+
 
 def send_change_stream_message_retention_days_notification(
     user_profile: UserProfile, stream: Stream, old_value: Optional[int], new_value: Optional[int]

zerver/tests/test_events.py

@@ -2532,9 +2532,12 @@ class SubscribeActionTest(BaseAction):
         )
         check_subscription_add("events[0]", events[0])
 
-        action = lambda: do_change_stream_description(stream, "new description")
-        events = self.verify_action(action, include_subscribers=include_subscribers)
+        action = lambda: do_change_stream_description(
+            stream, "new description", acting_user=self.example_user("hamlet")
+        )
+        events = self.verify_action(action, include_subscribers=include_subscribers, num_events=2)
         check_stream_update("events[0]", events[0])
+        check_message("events[1]", events[1])
 
         # Update stream privacy - make stream web public
         action = lambda: do_change_stream_permission(

zerver/tests/test_subs.py

@@ -879,7 +879,7 @@ class StreamAdminTest(ZulipTestCase):
         self.subscribe(self.example_user("cordelia"), "private_stream")
 
         events: List[Mapping[str, Any]] = []
-        with self.tornado_redirected_to_list(events, expected_num_events=1):
+        with self.tornado_redirected_to_list(events, expected_num_events=2):
             stream_id = get_stream("private_stream", user_profile.realm).id
             result = self.client_patch(
                 f"/json/streams/{stream_id}",
@@ -890,7 +890,7 @@ class StreamAdminTest(ZulipTestCase):
         cordelia = self.example_user("cordelia")
         prospero = self.example_user("prospero")
 
-        notified_user_ids = set(events[-1]["users"])
+        notified_user_ids = set(events[0]["users"])
         self.assertIn(user_profile.id, notified_user_ids)
         self.assertIn(cordelia.id, notified_user_ids)
         self.assertNotIn(prospero.id, notified_user_ids)
@@ -1158,7 +1158,7 @@ class StreamAdminTest(ZulipTestCase):
         self.subscribe(user_profile, "stream_name1")
 
         events: List[Mapping[str, Any]] = []
-        with self.tornado_redirected_to_list(events, expected_num_events=1):
+        with self.tornado_redirected_to_list(events, expected_num_events=2):
             stream_id = get_stream("stream_name1", realm).id
             result = self.client_patch(
                 f"/json/streams/{stream_id}",
@@ -1186,7 +1186,6 @@ class StreamAdminTest(ZulipTestCase):
         self.assertIn(user_profile.id, notified_user_ids)
         self.assertIn(self.example_user("prospero").id, notified_user_ids)
         self.assertNotIn(self.example_user("polonius").id, notified_user_ids)
-
         self.assertEqual("Test description", stream.description)
 
         result = self.client_patch(f"/json/streams/{stream_id}", {"description": "a" * 1025})
@@ -1203,6 +1202,20 @@ class StreamAdminTest(ZulipTestCase):
         stream = get_stream("stream_name1", realm)
         self.assertEqual(stream.description, "a multi line description")
 
+        messages = get_topic_messages(user_profile, stream, "stream events")
+        expected_notification = (
+            f"@_**{user_profile.full_name}|{user_profile.id}** changed the description for this stream.\n"
+            "Old description:\n"
+            "``` quote\n"
+            "Test description\n"
+            "```\n"
+            "New description:\n"
+            "``` quote\n"
+            "a multi line description\n"
+            "```"
+        )
+        self.assertEqual(messages[-1].content, expected_notification)
+
         # Verify that we don't render inline URL previews in this code path.
         with self.settings(INLINE_URL_EMBED_PREVIEW=True):
             result = self.client_patch(
@@ -1228,7 +1241,6 @@ class StreamAdminTest(ZulipTestCase):
             acting_user=None,
         )
 
-        with self.tornado_redirected_to_list(events, expected_num_events=1):
         stream_id = get_stream("stream_name1", realm).id
         result = self.client_patch(
             f"/json/streams/{stream_id}",
@@ -1238,6 +1250,20 @@ class StreamAdminTest(ZulipTestCase):
         stream = get_stream("stream_name1", realm)
         self.assertEqual(stream.description, "Test description")
 
+        messages = get_topic_messages(user_profile, stream, "stream events")
+        expected_notification = (
+            f"@_**{user_profile.full_name}|{user_profile.id}** changed the description for this stream.\n"
+            "Old description:\n"
+            "``` quote\n"
+            "See https://zulip.com/team\n"
+            "```\n"
+            "New description:\n"
+            "``` quote\n"
+            "Test description\n"
+            "```"
+        )
+        self.assertEqual(messages[-1].content, expected_notification)
+
     def test_change_stream_description_requires_admin(self) -> None:
         user_profile = self.example_user("hamlet")
         self.login_user(user_profile)

zerver/views/streams.py

@@ -284,7 +284,7 @@ def update_stream_backend(
         if "\n" in description:
             # We don't allow newline characters in stream descriptions.
             description = description.replace("\n", " ")
-        do_change_stream_description(stream, description)
+        do_change_stream_description(stream, description, acting_user=user_profile)
     if new_name is not None:
         new_name = new_name.strip()
         if stream.name == new_name: