Fix ModelHubMixin: save config only if doesn't exist (#2105)

* Fix ModelHubMixin: save config only if doesn't exist

* sutff

src/huggingface_hub/hub_mixin.py

@@ -248,13 +248,16 @@ def save_pretrained(
         # save model weights/files (framework-specific)
         self._save_pretrained(save_directory)
 
-        # save config (if provided)
+        # save config (if provided and if not serialized yet in `_save_pretrained`)
         if config is None:
             config = self.config
         if config is not None:
             if is_dataclass(config):
                 config = asdict(config)  # type: ignore[arg-type]
-            (save_directory / CONFIG_NAME).write_text(json.dumps(config, sort_keys=True, indent=2))
+            config_path = save_directory / CONFIG_NAME
+            if not config_path.exists():
+                config_str = json.dumps(config, sort_keys=True, indent=2)
+                config_path.write_text(config_str)
 
         # save model card
         model_card_path = save_directory / "README.md"

tests/test_hub_mixin.py

@@ -76,6 +76,15 @@ def __init__(self, **kwargs):
         pass
 
 
+class DummyModelSavingConfig(ModelHubMixin):
+    def _save_pretrained(self, save_directory: Path) -> None:
+        """Implementation that uses `config.json` to serialize the config.
+
+        This file must not be overwritten by the default config saved by `ModelHubMixin`.
+        """
+        (save_directory / "config.json").write_text(json.dumps({"custom_config": "custom_config"}))
+
+
 @pytest.mark.usefixtures("fx_cache_dir")
 class HubMixinTest(unittest.TestCase):
     cache_dir: Path
@@ -262,3 +271,11 @@ def test_push_to_hub(self):
 
         # Delete repo
         self._api.delete_repo(repo_id=repo_id)
+
+    def test_save_pretrained_do_not_overwrite_config(self):
+        """Regression test for https://github.com/huggingface/huggingface_hub/issues/2102."""
+        model = DummyModelSavingConfig()
+        model.save_pretrained(self.cache_dir)
+        # config.json is not overwritten
+        with open(self.cache_dir / "config.json") as f:
+            assert json.load(f) == {"custom_config": "custom_config"}

tests/test_hub_mixin_pytorch.py

@@ -290,6 +290,7 @@ def test_load_no_config(self):
         assert reloaded_with_default.state == "other"
         assert reloaded_with_default.config == {"num_classes": 50, "state": "other"}
 
+        config_file.unlink()  # Remove config file
         reloaded_with_default.save_pretrained(self.cache_dir)
         assert json.loads(config_file.read_text()) == {"num_classes": 50, "state": "other"}
 
@@ -307,6 +308,7 @@ def test_save_with_non_jsonable_config(self):
         assert "not_jsonable" not in model.config
 
         # If jsonable value passed by user, it's saved in the config
+        (self.cache_dir / "config.json").unlink()
         new_model = DummyModelNoConfig(not_jsonable=123)
         new_model.save_pretrained(self.cache_dir)
         assert new_model.config["not_jsonable"] == 123