Fix explicit position_ids generation on Transformers 4

modeling_ricursive.py

@@ -858,6 +858,25 @@ class RicursiveForCausalLM(RicursivePreTrainedModel, GenerationMixin):
             attentions=outputs.attentions,
         )
 
+    def _update_model_kwargs_for_generation(
+        self, outputs, model_kwargs, is_encoder_decoder=False, num_new_tokens=1
+    ):
+        """Advance explicit positions when the generation backend leaves them unchanged."""
+        position_ids = model_kwargs.get("position_ids")
+        model_kwargs = super()._update_model_kwargs_for_generation(
+            outputs, model_kwargs, is_encoder_decoder=is_encoder_decoder,
+            num_new_tokens=num_new_tokens,
+        )
+        # Transformers 4 leaves positions unchanged; Transformers 5 already extends them.
+        if position_ids is not None and model_kwargs.get("position_ids") is position_ids:
+            offsets = torch.arange(
+                1, num_new_tokens + 1, device=position_ids.device, dtype=position_ids.dtype
+            )
+            model_kwargs["position_ids"] = torch.cat(
+                [position_ids, position_ids[:, -1:] + offsets], dim=-1
+            )
+        return model_kwargs
+
     def prepare_inputs_for_generation(
         self,
         input_ids: torch.LongTensor,