mark_unread: Add support for empty topic name.

This commit is a part of the work to support empty string
as a topic name.

Previously, empty string was not a valid topic name.

Now, mark unread operation supports empty topic name.

Adds backward compatibility for:
- `topic` field in the `update_message_flags` event type
   when removing `read` flag

api_docs/changelog.md

@@ -43,6 +43,7 @@ format used by the Zulip server that they are interacting with.
     * `orig_subject` and `subject` fields in the `update_message` event type
     * `topic_name` field in the `user_topic` event type
     * `topic` field in the `typing` event type
+    * `topic` field in the `update_message_flags` event type when removing `read` flag
 
 * [`GET /messages`](/api/get-messages),
   [`GET /messages/{message_id}`](/api/get-message): Added `allow_empty_topic_name`

zerver/openapi/zulip.yaml

@@ -3129,6 +3129,17 @@ paths:
                                           Present only if `type` is `"stream"`.
 
                                           Name of the topic where the message was sent.
+
+                                          For clients that don't support the `empty_topic_name` [client capability][client-capabilities],
+                                          if the actual topic name is empty string, this field's value will instead
+                                          be the value of `realm_empty_topic_display_name` found in the
+                                          [`POST /register`](/api/register-queue) response.
+
+                                          **Changes**: Before 10.0 (feature level 334), `empty_topic_name`
+                                          client capability didn't exist and empty string as the topic name for
+                                          channel messages wasn't allowed.
+
+                                          [client-capabilities]: /api/register-queue#parameter-client_capabilities
                                       unmuted_stream_msg:
                                         type: boolean
                                         deprecated: true

zerver/tests/test_message_topics.py

@@ -377,7 +377,14 @@ class EmptyTopicNameTest(ZulipTestCase):
             apply_markdown=True,
             client_type_name="website",
             empty_topic_name=True,
-            event_types=["message", "update_message", "delete_message", "user_topic", "typing"],
+            event_types=[
+                "message",
+                "update_message",
+                "delete_message",
+                "user_topic",
+                "typing",
+                "update_message_flags",
+            ],
             last_connection_time=time.time(),
             queue_timeout=600,
             realm_id=hamlet.realm.id,
@@ -425,10 +432,10 @@ class EmptyTopicNameTest(ZulipTestCase):
         self.assertEqual(events[5]["topic"], "")
 
         # reset
-        self.send_stream_message(
+        message_id = self.send_stream_message(
             iago, "Denmark", topic_name="", skip_capture_on_commit_callbacks=True
         )
-        self.send_stream_message(
+        message_id_2 = self.send_stream_message(
             iago,
             "Verona",
             topic_name=Message.EMPTY_TOPIC_FALLBACK_NAME,
@@ -473,6 +480,25 @@ class EmptyTopicNameTest(ZulipTestCase):
         self.assertEqual(events[8]["topic"], "")
         self.assertEqual(events[9]["topic"], "")
 
+        # Prep to mark it as read before marking it as unread.
+        params = {
+            "messages": orjson.dumps([message_id, message_id_2]).decode(),
+            "op": "add",
+            "flag": "read",
+        }
+        self.client_post("/json/messages/flags", params)
+
+        with self.captureOnCommitCallbacks(execute=True):
+            params = {
+                "messages": orjson.dumps([message_id, message_id_2]).decode(),
+                "op": "remove",
+                "flag": "read",
+            }
+            self.client_post("/json/messages/flags", params)
+        events = client.event_queue.contents()
+        self.assertEqual(events[10]["message_details"][str(message_id)]["topic"], "")
+        self.assertEqual(events[10]["message_details"][str(message_id_2)]["topic"], "")
+
     def test_client_not_supports_empty_topic_name(self) -> None:
         iago = self.example_user("iago")
         hamlet = self.example_user("hamlet")
@@ -481,7 +507,14 @@ class EmptyTopicNameTest(ZulipTestCase):
             apply_markdown=True,
             client_type_name="zulip-mobile",
             empty_topic_name=False,
-            event_types=["message", "update_message", "delete_message", "user_topic", "typing"],
+            event_types=[
+                "message",
+                "update_message",
+                "delete_message",
+                "user_topic",
+                "typing",
+                "update_message_flags",
+            ],
             last_connection_time=time.time(),
             queue_timeout=600,
             realm_id=hamlet.realm.id,
@@ -529,10 +562,10 @@ class EmptyTopicNameTest(ZulipTestCase):
         self.assertEqual(events[5]["topic"], Message.EMPTY_TOPIC_FALLBACK_NAME)
 
         # reset
-        self.send_stream_message(
+        message_id = self.send_stream_message(
             iago, "Denmark", topic_name="", skip_capture_on_commit_callbacks=True
         )
-        self.send_stream_message(
+        message_id_2 = self.send_stream_message(
             iago,
             "Verona",
             topic_name=Message.EMPTY_TOPIC_FALLBACK_NAME,
@@ -577,6 +610,31 @@ class EmptyTopicNameTest(ZulipTestCase):
         self.assertEqual(events[8]["topic"], Message.EMPTY_TOPIC_FALLBACK_NAME)
         self.assertEqual(events[9]["topic"], Message.EMPTY_TOPIC_FALLBACK_NAME)
 
+        # Prep to mark it as read before marking it as unread.
+        params = {
+            "messages": orjson.dumps([message_id, message_id_2]).decode(),
+            "op": "add",
+            "flag": "read",
+        }
+        self.client_post("/json/messages/flags", params)
+
+        with self.captureOnCommitCallbacks(execute=True):
+            params = {
+                "messages": orjson.dumps([message_id, message_id_2]).decode(),
+                "op": "remove",
+                "flag": "read",
+            }
+            self.client_post("/json/messages/flags", params)
+        events = client.event_queue.contents()
+        self.assertEqual(
+            events[10]["message_details"][str(message_id)]["topic"],
+            Message.EMPTY_TOPIC_FALLBACK_NAME,
+        )
+        self.assertEqual(
+            events[10]["message_details"][str(message_id_2)]["topic"],
+            Message.EMPTY_TOPIC_FALLBACK_NAME,
+        )
+
     def test_fetch_messages(self) -> None:
         hamlet = self.example_user("hamlet")
         self.login_user(hamlet)

zerver/tornado/event_queue.py

@@ -1663,6 +1663,25 @@ def process_stream_typing_notification_event(
                 client.add_event(empty_topic_name_fallback_event)
 
 
+def process_mark_message_unread_event(event: Mapping[str, Any], users: Iterable[int]) -> None:
+    empty_topic_name_fallback_event = copy.deepcopy(dict(event))
+    for message_id, message_detail in empty_topic_name_fallback_event["message_details"].items():
+        if message_detail["type"] == "stream" and message_detail.get("topic") == "":
+            empty_topic_name_fallback_event["message_details"][message_id]["topic"] = (
+                Message.EMPTY_TOPIC_FALLBACK_NAME
+            )
+
+    for user_profile_id in users:
+        for client in get_client_descriptors_for_user(user_profile_id):
+            if not client.accepts_event(event):
+                continue
+
+            if client.empty_topic_name:
+                client.add_event(event)
+            else:
+                client.add_event(empty_topic_name_fallback_event)
+
+
 def process_notification(notice: Mapping[str, Any]) -> None:
     event: Mapping[str, Any] = notice["event"]
     users: list[int] | list[Mapping[str, Any]] = notice["users"]
@@ -1695,6 +1714,12 @@ def process_notification(notice: Mapping[str, Any]) -> None:
         process_user_topic_event(event, cast(list[int], users))
     elif event["type"] == "typing" and event["message_type"] == "stream":
         process_stream_typing_notification_event(event, cast(list[int], users))
+    elif (
+        event["type"] == "update_message_flags"
+        and event["op"] == "remove"
+        and event["flag"] == "read"
+    ):
+        process_mark_message_unread_event(event, cast(list[int], users))
     elif event["type"] == "cleanup_queue":
         # cleanup_event_queue may generate this event to forward cleanup
         # requests to the right shard.