message_delete: Update "first_message_id" on message deletion.

We now "first_message_id" of the stream on the deletion of the first
message that was sent to it. This results in 1 extra query when any
stream message is deleted and 3 extra queries when the first message
sent to any stream is deleted.

Fixes #28877.

api_docs/changelog.md

@@ -20,6 +20,11 @@ format used by the Zulip server that they are interacting with.
 
 ## Changes in Zulip 9.0
 
+**Feature level 256**
+
+* [`GET /events`](/api/get-events): Stream update events with a new
+  `first_message_id` may now be sent when messages are deleted.
+
 **Feature level 255**
 
 * "Stream" was renamed to "Channel" across strings in the Zulip API

version.py

@@ -33,7 +33,7 @@ DESKTOP_WARNING_VERSION = "5.9.3"
 # Changes should be accompanied by documentation explaining what the
 # new level means in api_docs/changelog.md, as well as "**Changes**"
 # entries in the endpoint's documentation in `zulip.yaml`.
-API_FEATURE_LEVEL = 255
+API_FEATURE_LEVEL = 256
 
 # Bump the minor PROVISION_VERSION to indicate that folks should provision
 # only when going from an old version of the code to a newer version. Bump

zerver/actions/message_delete.py

@@ -3,7 +3,7 @@ from typing import Iterable, List, TypedDict
 from zerver.lib import retention
 from zerver.lib.retention import move_messages_to_archive
 from zerver.lib.stream_subscription import get_active_subscriptions_for_stream_id
-from zerver.models import Message, Realm, UserMessage, UserProfile
+from zerver.models import Message, Realm, Stream, UserMessage, UserProfile
 from zerver.tornado.django_api import send_event_on_commit
 
 
@@ -15,6 +15,34 @@ class DeleteMessagesEvent(TypedDict, total=False):
     stream_id: int
 
 
+def check_update_first_message_id(
+    realm: Realm, stream: Stream, message_ids: List[int], users_to_notify: Iterable[int]
+) -> None:
+    # This will not update the `first_message_id` of streams where the
+    # first message was deleted prior to the implementation of this function.
+    assert stream.recipient_id is not None
+    if stream.first_message_id not in message_ids:
+        return
+    current_first_message_id = (
+        Message.objects.filter(realm_id=realm.id, recipient_id=stream.recipient_id)
+        .values_list("id", flat=True)
+        .order_by("id")
+        .first()
+    )
+
+    stream.first_message_id = current_first_message_id
+    stream.save(update_fields=["first_message_id"])
+
+    stream_event = dict(
+        type="stream",
+        op="update",
+        property="first_message_id",
+        value=stream.first_message_id,
+        stream_id=stream.id,
+    )
+    send_event_on_commit(realm, stream_event, users_to_notify)
+
+
 def do_delete_messages(realm: Realm, messages: Iterable[Message]) -> None:
     # messages in delete_message event belong to the same topic
     # or is a single direct message, as any other behaviour is not possible with
@@ -52,6 +80,9 @@ def do_delete_messages(realm: Realm, messages: Iterable[Message]) -> None:
         archiving_chunk_size = retention.STREAM_MESSAGE_BATCH_SIZE
 
     move_messages_to_archive(message_ids, realm=realm, chunk_size=archiving_chunk_size)
+    if message_type == "stream":
+        stream = Stream.objects.get(id=sample_message.recipient.type_id)
+        check_update_first_message_id(realm, stream, message_ids, users_to_notify)
 
     event["message_type"] = message_type
     send_event_on_commit(realm, event, users_to_notify)

zerver/openapi/zulip.yaml

@@ -18080,7 +18080,11 @@ paths:
         response. If all messages in the topic were deleted, then the success
         response will return `"complete": true`.
 
-        **Changes**: Before Zulip 8.0 (feature level 211), if the server's
+        **Changes**: Before Zulip 9.0 (feature level 256), the server never sent
+        events updating the `first_message_id` for a stream when the oldest
+        message that had been sent to it changed.
+
+        Before Zulip 8.0 (feature level 211), if the server's
         processing was interrupted by a timeout, but some messages in the topic
         were deleted, then it would return `"result": "partially_completed"`,
         along with a `code` field for an error string, in the success response

zerver/tests/test_message_delete.py

@@ -11,6 +11,7 @@ from zerver.actions.realm_settings import do_set_realm_property
 from zerver.lib.test_classes import ZulipTestCase
 from zerver.models import Message, Realm, UserProfile
 from zerver.models.realms import get_realm
+from zerver.models.streams import get_stream
 
 if TYPE_CHECKING:
     from django.test.client import _MonkeyPatchedWSGIResponse as TestHttpResponse
@@ -321,3 +322,28 @@ class DeleteMessageTest(ZulipTestCase):
         result = self.client_delete(f"/json/messages/{msg_id}")
         self.assert_json_success(result)
         self.assertFalse(Message.objects.filter(id=msg_id).exists())
+
+    def test_update_first_message_id_on_stream_message_deletion(self) -> None:
+        realm = get_realm("zulip")
+        stream_name = "test"
+        cordelia = self.example_user("cordelia")
+        self.make_stream(stream_name)
+        self.subscribe(cordelia, stream_name)
+        message_ids = [self.send_stream_message(cordelia, stream_name) for _ in range(5)]
+        first_message_id = message_ids[0]
+
+        message = Message.objects.get(id=message_ids[3])
+        do_delete_messages(realm, [message])
+        stream = get_stream(stream_name, realm)
+        self.assertEqual(stream.first_message_id, first_message_id)
+
+        first_message = Message.objects.get(id=first_message_id)
+        do_delete_messages(realm, [first_message])
+        stream = get_stream(stream_name, realm)
+        self.assertEqual(stream.first_message_id, message_ids[1])
+
+        all_messages = Message.objects.filter(id__in=message_ids)
+        with self.assert_database_query_count(23):
+            do_delete_messages(realm, all_messages)
+        stream = get_stream(stream_name, realm)
+        self.assertEqual(stream.first_message_id, None)

zerver/tests/test_retention.py

@@ -1138,7 +1138,7 @@ class TestDoDeleteMessages(ZulipTestCase):
         message_ids = [self.send_stream_message(cordelia, "Verona", str(i)) for i in range(10)]
         messages = Message.objects.filter(id__in=message_ids)
 
-        with self.assert_database_query_count(20):
+        with self.assert_database_query_count(21):
             do_delete_messages(realm, messages)
         self.assertFalse(Message.objects.filter(id__in=message_ids).exists())