Fix AttributeError in CommandSyncFailure due to APPLICATION_COMMAND_TOO_LARGE

discord/app_commands/errors.py

@@ -530,6 +530,16 @@ class CommandSyncFailure(AppCommandError, HTTPException):
         messages = [f'Failed to upload commands to Discord (HTTP status {self.status}, error code {self.code})']
 
         if self._errors:
+            # Handle case where the errors dict has no actual chain such as APPLICATION_COMMAND_TOO_LARGE
+            if len(self._errors) == 1 and '_errors' in self._errors:
+                errors = self._errors['_errors']
+                if len(errors) == 1:
+                    extra = errors[0].get('message')
+                    if extra:
+                        messages[0] += f': {extra}'
+                else:
+                    messages.extend(f'Error {e.get("code", "")}: {e.get("message", "")}' for e in errors)
+            else:
                 for index, inner in self._errors.items():
                     _get_command_error(index, inner, commands, messages)