message_edit: Topic and stream editing do not depend on allow_message_editing.

We change the topic and stream edit permssions to not depend on
allow_message_editing setting in the API and are allowed even
if allow_message_editing is set to False based on other settings
like edit_topic_policy and can_move_message_between_streams.

Fixes a part of #21739.

templates/zerver/api/changelog.md

@@ -28,6 +28,8 @@ format used by the Zulip server that they are interacting with.
 * [`POST /register`](/api/register-queue), [`GET /events`](/api/get-events),
   `PATCH /realm`: Nobody added as an option for the realm setting
   `move_messages_between_streams_policy`.
+* [`PATCH /messages/{message_id}`](/api/update-message): Permission to edit stream
+  and topic of messages do not depend on `allow_message_editing` setting now.
 
 Feature levels 157-158 are reserved for future use in 6.x maintenance
 releases.

zerver/actions/message_edit.py

@@ -918,7 +918,7 @@ def check_update_message(
     """
     message, ignored_user_message = access_message(user_profile, message_id)
 
-    if not user_profile.realm.allow_message_editing:
+    if content is not None and not user_profile.realm.allow_message_editing:
         raise JsonableError(_("Your organization has turned off message editing"))
 
     # The zerver/views/message_edit.py call point already strips this

zerver/openapi/zulip.yaml

@@ -6460,6 +6460,11 @@ paths:
         **Note**: See [configuring message editing][config-message-editing]
         for detailed documentation on when users are allowed to edit topics.
 
+        **Changes**: Before Zulip 7.0 (feature level 159), editing
+        streams and topics of messages was forbidden if
+        `allow_message_editing` was `false`, regardless of the
+        `edit_topic_policy` or `move_messages_between_streams_policy`.
+
         [config-message-editing]: /help/configure-message-editing-and-deletion
       x-curl-examples-parameters:
         oneOf:

zerver/tests/test_message_edit.py

@@ -1043,19 +1043,18 @@ class EditMessageTest(EditMessageTestCase):
         set_message_editing_params(True, "unlimited", Realm.POLICY_ADMINS_ONLY)
         do_edit_message_assert_success(id_, "D")
 
-        # without allow_message_editing, nothing is allowed
+        # without allow_message_editing, editing content is not allowed but
+        # editing topic is allowed if topic-edit time limit has not passed
+        # irrespective of content-edit time limit.
         set_message_editing_params(False, 240, Realm.POLICY_ADMINS_ONLY)
-        do_edit_message_assert_error(
+        do_edit_message_assert_success(id_, "B", True)
-            id_, "E", "Your organization has turned off message editing", True
+
-        )
+        set_message_editing_params(False, 240, Realm.POLICY_ADMINS_ONLY)
+        do_edit_message_assert_success(id_, "E", True)
         set_message_editing_params(False, 120, Realm.POLICY_ADMINS_ONLY)
-        do_edit_message_assert_error(
+        do_edit_message_assert_success(id_, "F", True)
-            id_, "F", "Your organization has turned off message editing", True
-        )
         set_message_editing_params(False, "unlimited", Realm.POLICY_ADMINS_ONLY)
-        do_edit_message_assert_error(
+        do_edit_message_assert_success(id_, "G", True)
-            id_, "G", "Your organization has turned off message editing", True
-        )
 
     def test_edit_topic_policy(self) -> None:
         def set_message_editing_params(
@@ -1162,11 +1161,9 @@ class EditMessageTest(EditMessageTestCase):
             id_, "H", "You don't have permission to edit this message", "iago"
         )
 
-        # users cannot edit topics if allow_message_editing is False
+        # users can edit topics even if allow_message_editing is False
         set_message_editing_params(False, "unlimited", Realm.POLICY_EVERYONE)
-        do_edit_message_assert_error(
+        do_edit_message_assert_success(id_, "D", "cordelia")
-            id_, "D", "Your organization has turned off message editing", "cordelia"
-        )
 
         # non-admin users cannot edit topics sent > 72 hrs ago
         message.date_sent = message.date_sent - datetime.timedelta(seconds=290000)