edit_history: 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.

Adds `allow_empty_topic_name` boolean parameter to
`GET /messages/{message_id}/history` endpoint to decide whether
the topic names in the fetched messages can be empty strings.

If False, the topic names in the fetched response will have the
value of `realm_empty_topic_display_name` field in `POST /register`
response replacing "" for channel messages.

api_docs/changelog.md

@@ -49,6 +49,10 @@ format used by the Zulip server that they are interacting with.
   boolean parameter to decide whether the topic names in the fetched messages
   can be empty strings.
 
+* [`GET /messages/{message_id}/history`](/api/get-message-history):
+  Added `allow_empty_topic_name` boolean parameter to decide whether the
+  topic names in the fetched message history objects can be empty strings.
+
 **Feature level 333**
 
 * [Message formatting](/api/message-formatting): System groups can now

zerver/lib/topic.py

@@ -327,3 +327,11 @@ def maybe_rename_general_chat_to_empty_topic(topic_name: str) -> str:
     if topic_name == Message.EMPTY_TOPIC_FALLBACK_NAME:
         topic_name = ""
     return topic_name
+
+
+def maybe_rename_empty_topic_to_general_chat(
+    topic_name: str, is_channel_message: bool, allow_empty_topic_name: bool
+) -> str:
+    if is_channel_message and topic_name == "" and not allow_empty_topic_name:
+        return Message.EMPTY_TOPIC_FALLBACK_NAME
+    return topic_name

zerver/openapi/zulip.yaml

@@ -7310,6 +7310,21 @@ paths:
         [edit-settings]: /help/view-a-messages-edit-history
       parameters:
         - $ref: "#/components/parameters/MessageId"
+        - name: allow_empty_topic_name
+          in: query
+          description: |
+            Whether the topic names i.e. `topic` and `prev_topic` fields in
+            the `message_history` objects returned can be empty string.
+
+            If `false`, the value of `realm_empty_topic_display_name`
+            found in the [`POST /register`](/api/register-queue) response is
+            returned replacing the empty string as the topic name.
+
+            **Changes**: New in Zulip 10.0 (feature level 334).
+          schema:
+            type: boolean
+            default: false
+          example: true
       x-response-description: |
         Please note that the original message's snapshot only contains the fields
         `topic`, `content`, `rendered_content`, `timestamp` and `user_id`. This

zerver/tests/test_message_topics.py

@@ -686,3 +686,44 @@ class EmptyTopicNameTest(ZulipTestCase):
         )
         data = self.assert_json_success(result)
         self.assertEqual(data["message"]["edit_history"][0]["topic"], "")
+
+    def test_get_message_edit_history(self) -> None:
+        hamlet = self.example_user("hamlet")
+        self.login_user(hamlet)
+
+        message_id = self.send_stream_message(hamlet, "Denmark", topic_name="")
+        message_id_2 = self.send_stream_message(
+            hamlet, "Denmark", topic_name=Message.EMPTY_TOPIC_FALLBACK_NAME
+        )
+
+        params = {"topic": "new topic name"}
+        result = self.client_patch(f"/json/messages/{message_id}", params)
+        self.assert_json_success(result)
+        result = self.client_patch(f"/json/messages/{message_id_2}", params)
+        self.assert_json_success(result)
+
+        params = {"allow_empty_topic_name": "false"}
+        result = self.client_get(f"/json/messages/{message_id}/history", params)
+        data = self.assert_json_success(result)
+        self.assertEqual(data["message_history"][0]["topic"], Message.EMPTY_TOPIC_FALLBACK_NAME)
+        self.assertEqual(
+            data["message_history"][1]["prev_topic"], Message.EMPTY_TOPIC_FALLBACK_NAME
+        )
+
+        result = self.client_get(f"/json/messages/{message_id_2}/history", params)
+        data = self.assert_json_success(result)
+        self.assertEqual(data["message_history"][0]["topic"], Message.EMPTY_TOPIC_FALLBACK_NAME)
+        self.assertEqual(
+            data["message_history"][1]["prev_topic"], Message.EMPTY_TOPIC_FALLBACK_NAME
+        )
+
+        params = {"allow_empty_topic_name": "true"}
+        result = self.client_get(f"/json/messages/{message_id}/history", params)
+        data = self.assert_json_success(result)
+        self.assertEqual(data["message_history"][0]["topic"], "")
+        self.assertEqual(data["message_history"][1]["prev_topic"], "")
+
+        result = self.client_get(f"/json/messages/{message_id_2}/history", params)
+        data = self.assert_json_success(result)
+        self.assertEqual(data["message_history"][0]["topic"], "")
+        self.assertEqual(data["message_history"][1]["prev_topic"], "")

zerver/views/message_edit.py

@@ -23,13 +23,16 @@ from zerver.lib.message import (
 from zerver.lib.request import RequestNotes
 from zerver.lib.response import json_success
 from zerver.lib.timestamp import datetime_to_timestamp
+from zerver.lib.topic import maybe_rename_empty_topic_to_general_chat
 from zerver.lib.typed_endpoint import OptionalTopic, PathOnly, typed_endpoint
 from zerver.lib.types import EditHistoryEvent, FormattedEditHistoryEvent
 from zerver.models import Message, UserProfile
 
 
 def fill_edit_history_entries(
-    raw_edit_history: list[EditHistoryEvent], message: Message
+    raw_edit_history: list[EditHistoryEvent],
+    message: Message,
+    allow_empty_topic_name: bool,
 ) -> list[FormattedEditHistoryEvent]:
     """
     This fills out the message edit history entries from the database
@@ -39,7 +42,10 @@ def fill_edit_history_entries(
     """
     prev_content = message.content
     prev_rendered_content = message.rendered_content
-    prev_topic_name = message.topic_name()
+    is_channel_message = message.is_stream_message()
+    prev_topic_name = maybe_rename_empty_topic_to_general_chat(
+        message.topic_name(), is_channel_message, allow_empty_topic_name
+    )
 
     # Make sure that the latest entry in the history corresponds to the
     # message's last edit time
@@ -58,7 +64,9 @@ def fill_edit_history_entries(
         }
 
         if "prev_topic" in edit_history_event:
-            prev_topic_name = edit_history_event["prev_topic"]
+            prev_topic_name = maybe_rename_empty_topic_to_general_chat(
+                edit_history_event["prev_topic"], is_channel_message, allow_empty_topic_name
+            )
             formatted_entry["prev_topic"] = prev_topic_name
 
         # Fill current values for content/rendered_content.
@@ -99,6 +107,7 @@ def get_message_edit_history(
     user_profile: UserProfile,
     *,
     message_id: PathOnly[NonNegativeInt],
+    allow_empty_topic_name: Json[bool] = False,
 ) -> HttpResponse:
     if not user_profile.realm.allow_edit_history:
         raise JsonableError(_("Message edit history is disabled in this organization"))
@@ -111,7 +120,9 @@ def get_message_edit_history(
         raw_edit_history = []
 
     # Fill in all the extra data that will make it usable
-    message_edit_history = fill_edit_history_entries(raw_edit_history, message)
+    message_edit_history = fill_edit_history_entries(
+        raw_edit_history, message, allow_empty_topic_name
+    )
     return json_success(request, data={"message_history": list(reversed(message_edit_history))})