RWKV: raise informative exception when attempting to manipulate `past_key_values` (#28600)

src/transformers/models/rwkv/modeling_rwkv.py

@@ -778,6 +778,24 @@ class RwkvForCausalLM(RwkvPreTrainedModel):
     def set_output_embeddings(self, new_embeddings):
         self.head = new_embeddings
 
+    def generate(self, *args, **kwargs):
+        # Thin wrapper to raise exceptions when trying to generate with methods that manipulate `past_key_values`.
+        # RWKV is one of the few models that don't have it (it has `state` instead, which has different properties and
+        # usage).
+        try:
+            gen_output = super().generate(*args, **kwargs)
+        except AttributeError as exc:
+            # Expected exception: "AttributeError: '(object name)' object has no attribute 'past_key_values'"
+            if "past_key_values" in str(exc):
+                raise AttributeError(
+                    "You tried to call `generate` with a decoding strategy that manipulates `past_key_values`. RWKV "
+                    "doesn't have that attribute, try another generation strategy instead. For the available "
+                    "generation strategies, check this doc: https://huggingface.co/docs/transformers/en/generation_strategies#decoding-strategies"
+                )
+            else:
+                raise exc
+        return gen_output
+
     def prepare_inputs_for_generation(self, input_ids, state=None, inputs_embeds=None, **kwargs):
         # only last token for inputs_ids if the state is passed along.
         if state is not None: