Throw error when inferencing longer than max_popsition_embeddings (#1236)

* Throw error when inferencing longer than max_popsition_embeddings without rope scaling

* Update llama.py

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Co-authored-by: Daniel Han <danielhanchen@gmail.com>

unsloth/models/llama.py

@@ -1376,6 +1376,15 @@ def _wrap_fast_inference(generate, device_type, dtype, model):
     @torch.inference_mode
     def _fast_generate(*args, **kwargs):
 
+        if hasattr(model, "config") and hasattr(model.config, "max_position_embeddings"):
+            if "input_ids" in kwargs and kwargs["input_ids"] is not None and "max_new_tokens" in kwargs:
+                if kwargs["input_ids"].shape[-1] + kwargs["max_new_tokens"] > model.config.max_position_embeddings:
+                    raise ValueError(
+                        f'Unsloth: input length {kwargs["input_ids"].shape[-1]} + max_new_tokens {kwargs["max_new_tokens"]} exceeds the maximum sequence length of {model.config.max_position_embeddings}!\n'\
+                        'You will need to do long context extension by increasing the `max_seq_length` in `FastLanguageModel.from_pretrained`.'
+                    )
+        pass
+
         # Set a flag for generation!
         internal_model = model
         while hasattr(internal_model, "model"):