Fix cog_app_command_error for groups

discord/app_commands/commands.py

@@ -1269,6 +1269,10 @@ class Group:
                 raise ValueError('groups can only be nested at most one level')
             parent.add_command(self)
 
+        self.__app_commands_error_handler__: Optional[
+            Callable[[Interaction, AppCommandError], Coroutine[Any, Any, None]]
+        ] = None
+
     def __set_name__(self, owner: Type[Any], name: str) -> None:
         self._attr = name
         self.module = owner.__module__

discord/ext/commands/cog.py

@@ -328,6 +328,13 @@ class Cog(metaclass=CogMeta):
                     if self.__cog_app_commands_group__:
                         children.append(app_command)
 
+        if Cog._get_overridden_method(self.cog_app_command_error) is not None:
+            error_handler = self.cog_app_command_error
+        else:
+            error_handler = None
+
+        self.__app_commands_error_handler__ = error_handler
+
         for command in cls.__cog_app_commands__:
             copy = command._copy_with(parent=self.__cog_app_commands_group__, binding=self)
 
@@ -335,6 +342,9 @@ class Cog(metaclass=CogMeta):
             if copy._attr:
                 setattr(self, copy._attr, copy)
 
+            if isinstance(copy, app_commands.Group):
+                copy.__app_commands_error_handler__ = error_handler
+
             children.append(copy)
 
         self.__cog_app_commands__ = children
@@ -346,11 +356,6 @@ class Cog(metaclass=CogMeta):
 
             self.__cog_app_commands_group__._children = mapping  # type: ignore  # Variance issue
 
-        if Cog._get_overridden_method(self.cog_app_command_error) is not None:
-            self.__app_commands_error_handler__ = self.cog_app_command_error
-        else:
-            self.__app_commands_error_handler__ = None
-
         return self
 
     def get_commands(self) -> List[Command[Self, ..., Any]]: