fix #1494

Former-commit-id: 07c8d734529f03e47ef638a1bda222e8824d3d38

src/llmtuner/hparams/data_args.py

@@ -52,6 +52,10 @@ class DataArguments:
         default=1024,
         metadata={"help": "The maximum length of the model inputs after tokenization."}
     )
+    reserved_label_len: Optional[int] = field(
+        default=1,
+        metadata={"help": "The maximum length reserved for label after tokenization."}
+    )
     train_on_prompt: Optional[bool] = field(
         default=False,
         metadata={"help": "Whether to disable the mask on the prompt or not."}
@@ -110,6 +114,9 @@ class DataArguments:
     )
 
     def __post_init__(self):
+        if self.reserved_label_len >= self.cutoff_len:
+            raise ValueError("`reserved_label_len` must be smaller than `cutoff_len`.")
+
         if self.streaming and self.val_size > 1e-6 and self.val_size < 1:
             raise ValueError("Streaming mode should have an integer val size.")