support PeftMixedModel signature inspect (#28321)

* support PeftMixedModel signature inspect

* import PeftMixedModel only peft>=0.7.0

* Update src/transformers/trainer.py
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>

* Update src/transformers/trainer.py
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>

* Update src/transformers/trainer.py
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>

* Update src/transformers/trainer.py
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>

* Update src/transformers/trainer.py
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>

* Update src/transformers/trainer.py
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>

* fix styling

* Update src/transformers/trainer.py
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>

* Update src/transformers/trainer.py
Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>

* style fixup

* fix note

---------
Co-authored-by: Younes Belkada <49240599+younesbelkada@users.noreply.github.com>
Co-authored-by: Arthur <48595927+ArthurZucker@users.noreply.github.com>

src/transformers/trainer.py

@@ -185,7 +185,6 @@ else:
 if is_safetensors_available():
     import safetensors.torch
 
-
 if is_peft_available():
     from peft import PeftModel
 
@@ -213,7 +212,15 @@ if is_accelerate_available():
 
 
 def _is_peft_model(model):
-    return is_peft_available() and isinstance(model, PeftModel)
+    if is_peft_available():
+        classes_to_check = (PeftModel,) if is_peft_available() else ()
+        # Here we also check if the model is an instance of `PeftMixedModel` introduced in peft>=0.7.0: https://github.com/huggingface/transformers/pull/28321
+        if version.parse(importlib.metadata.version("peft")) >= version.parse("0.7.0"):
+            from peft import PeftMixedModel
+
+            classes_to_check = (*classes_to_check, PeftMixedModel)
+        return isinstance(model, classes_to_check)
+    return False
 
 
 if TYPE_CHECKING:
@@ -700,7 +707,11 @@ class Trainer:
             # Inspect model forward signature to keep only the arguments it accepts.
             model_to_inspect = self.model
             if _is_peft_model(self.model):
-                model_to_inspect = self.model.get_base_model()
+                if hasattr(self.model, "get_base_model"):
+                    model_to_inspect = self.model.get_base_model()
+                else:
+                    # PeftMixedModel do not provide a `get_base_model` method
+                    model_to_inspect = self.model.base_model.model
             signature = inspect.signature(model_to_inspect.forward)
             self._signature_columns = list(signature.parameters.keys())
             # Labels may be named label or label_ids, the default data collator handles that.