Config: warning when saving generation kwargs in the model config (#28514)

tests/generation/test_framework_agnostic.py

@@ -529,7 +529,7 @@ class GenerationIntegrationTestsMixin:
 
         pixel_values = floats_tensor((2, 3, 30, 30))
         model = model_cls.from_pretrained("hf-internal-testing/tiny-random-VisionEncoderDecoderModel-vit-gpt2")
-        model.config.decoder.eos_token_id = None
+        model.generation_config.eos_token_id = None
         if is_pt:
             pixel_values = pixel_values.to(torch_device)
             model = model.to(torch_device)

tests/test_configuration_utils.py

@@ -296,3 +296,19 @@ class ConfigTestUtils(unittest.TestCase):
         old_transformers.configuration_utils.__version__ = "v3.0.0"
         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_warning(self):
+        config = BertConfig(min_length=3)  # `min_length = 3` is a non-default generation kwarg
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            with self.assertLogs("transformers.configuration_utils", level="WARNING") as logs:
+                config.save_pretrained(tmp_dir)
+            self.assertEqual(len(logs.output), 1)
+            self.assertIn("min_length", logs.output[0])
+
+    def test_has_non_default_generation_parameters(self):
+        config = BertConfig()
+        self.assertFalse(config._has_non_default_generation_parameters())
+        config = BertConfig(min_length=3)
+        self.assertTrue(config._has_non_default_generation_parameters())
+        config = BertConfig(min_length=0)  # `min_length = 0` is a default generation kwarg
+        self.assertFalse(config._has_non_default_generation_parameters())

tests/test_modeling_utils.py

@@ -1230,6 +1230,15 @@ class ModelUtilsTest(TestCasePlus):
         for p1, p2 in zip(model.parameters(), new_model.parameters()):
             self.assertTrue(torch.equal(p1, p2))
 
+    def test_modifying_model_config_causes_warning_saving_generation_config(self):
+        model = AutoModelForCausalLM.from_pretrained("gpt2")
+        model.config.top_k = 1
+        with tempfile.TemporaryDirectory() as tmp_dir:
+            with self.assertLogs("transformers.modeling_utils", level="WARNING") as logs:
+                model.save_pretrained(tmp_dir)
+            self.assertEqual(len(logs.output), 1)
+            self.assertIn("Your generation config was originally created from the model config", logs.output[0])
+
 
 @slow
 @require_torch