Config: lower save_pretrained exception to warning (huggingface#33906)

* lower to warning

* msg

* make fixup

* rm extra comma

Author: gante

src/transformers/configuration_utils.py

@@ -380,11 +380,14 @@ def save_pretrained(self, save_directory: Union[str, os.PathLike], push_to_hub:
 
         non_default_generation_parameters = self._get_non_default_generation_parameters()
         if len(non_default_generation_parameters) > 0:
-            raise ValueError(
+            # TODO (joao): this should be an exception if the user has modified the loaded config. See #33886
+            warnings.warn(
                 "Some non-default generation parameters are set in the model config. These should go into either a) "
                 "`model.generation_config` (as opposed to `model.config`); OR b) a GenerationConfig file "
-                "(https://huggingface.co/docs/transformers/generation_strategies#save-a-custom-decoding-strategy-with-your-model) "
-                f"\nNon-default generation parameters: {str(non_default_generation_parameters)}"
+                "(https://huggingface.co/docs/transformers/generation_strategies#save-a-custom-decoding-strategy-with-your-model)."
+                "This warning will become an exception in the future."
+                f"\nNon-default generation parameters: {str(non_default_generation_parameters)}",
+                UserWarning,
             )
 
         os.makedirs(save_directory, exist_ok=True)

tests/utils/test_configuration_utils.py

@@ -313,11 +313,12 @@ def test_repo_versioning_before(self):
         old_configuration = old_transformers.models.auto.AutoConfig.from_pretrained(repo)
         self.assertEqual(old_configuration.hidden_size, 768)
 
-    def test_saving_config_with_custom_generation_kwargs_raises_exception(self):
+    def test_saving_config_with_custom_generation_kwargs_raises_warning(self):
         config = BertConfig(min_length=3)  # `min_length = 3` is a non-default generation kwarg
         with tempfile.TemporaryDirectory() as tmp_dir:
-            with self.assertRaises(ValueError):
+            with self.assertWarns(UserWarning) as cm:
                 config.save_pretrained(tmp_dir)
+            self.assertIn("min_length", str(cm.warning))
 
     def test_get_non_default_generation_parameters(self):
         config = BertConfig()