Fix typing.get_type_hints call on a ModelHubMixin (#2729)

* Add DataclassInstance for runtime type_checking

* Add suggestion from code review

* Fix type annotation

* Add test

* Actually fix type annotation (3.8)

---------

Co-authored-by: Celina Hanouti <hanouticelina@gmail.com>

src/huggingface_hub/hub_mixin.py

@@ -1,9 +1,9 @@
 import inspect
 import json
 import os
-from dataclasses import asdict, dataclass, is_dataclass
+from dataclasses import Field, asdict, dataclass, is_dataclass
 from pathlib import Path
-from typing import TYPE_CHECKING, Any, Callable, Dict, List, Optional, Tuple, Type, TypeVar, Union
+from typing import Any, Callable, ClassVar, Dict, List, Optional, Protocol, Tuple, Type, TypeVar, Union
 
 import packaging.version
 
@@ -24,9 +24,6 @@
 )
 
 
-if TYPE_CHECKING:
-    from _typeshed import DataclassInstance
-
 if is_torch_available():
     import torch  # type: ignore
 
@@ -38,6 +35,12 @@
 
 logger = logging.get_logger(__name__)
 
+
+# Type alias for dataclass instances, copied from https://github.com/python/typeshed/blob/9f28171658b9ca6c32a7cb93fbb99fc92b17858b/stdlib/_typeshed/__init__.pyi#L349
+class DataclassInstance(Protocol):
+    __dataclass_fields__: ClassVar[Dict[str, Field]]
+
+
 # Generic variable that is either ModelHubMixin or a subclass thereof
 T = TypeVar("T", bound="ModelHubMixin")
 # Generic variable to represent an args type
@@ -175,7 +178,7 @@ class ModelHubMixin:
     ```
     """
 
-    _hub_mixin_config: Optional[Union[dict, "DataclassInstance"]] = None
+    _hub_mixin_config: Optional[Union[dict, DataclassInstance]] = None
     # ^ optional config attribute automatically set in `from_pretrained`
     _hub_mixin_info: MixinInfo
     # ^ information about the library integrating ModelHubMixin (used to generate model card)
@@ -366,7 +369,7 @@ def save_pretrained(
         self,
         save_directory: Union[str, Path],
         *,
-        config: Optional[Union[dict, "DataclassInstance"]] = None,
+        config: Optional[Union[dict, DataclassInstance]] = None,
         repo_id: Optional[str] = None,
         push_to_hub: bool = False,
         model_card_kwargs: Optional[Dict[str, Any]] = None,
@@ -618,7 +621,7 @@ def push_to_hub(
         self,
         repo_id: str,
         *,
-        config: Optional[Union[dict, "DataclassInstance"]] = None,
+        config: Optional[Union[dict, DataclassInstance]] = None,
         commit_message: str = "Push model using huggingface_hub.",
         private: Optional[bool] = None,
         token: Optional[str] = None,
@@ -825,7 +828,7 @@ def _load_as_safetensor(cls, model: T, model_file: str, map_location: str, stric
         return model
 
 
-def _load_dataclass(datacls: Type["DataclassInstance"], data: dict) -> "DataclassInstance":
+def _load_dataclass(datacls: Type[DataclassInstance], data: dict) -> DataclassInstance:
     """Load a dataclass instance from a dictionary.
 
     Fields not expected by the dataclass are ignored.

tests/test_hub_mixin.py

@@ -4,7 +4,7 @@
 import unittest
 from dataclasses import dataclass
 from pathlib import Path
-from typing import Dict, Optional, Union
+from typing import Dict, Optional, Union, get_type_hints
 from unittest.mock import Mock, patch
 
 import jedi
@@ -474,3 +474,24 @@ def dummy_example_for_test(self, x: str) -> str:
         source_lines = source.split("\n")
         completions = script.complete(len(source_lines), len(source_lines[-1]))
         assert any(completion.name == "dummy_example_for_test" for completion in completions)
+
+    def test_get_type_hints_works_as_expected(self):
+        """
+        Ensure that `typing.get_type_hints` works as expected when inheriting from `ModelHubMixin`.
+
+        See https://github.com/huggingface/huggingface_hub/issues/2727.
+        """
+
+        class ModelWithHints(ModelHubMixin):
+            def method_with_hints(self, x: int) -> str:
+                return str(x)
+
+        assert get_type_hints(ModelWithHints) != {}
+
+        # Test method type hints on class
+        hints = get_type_hints(ModelWithHints.method_with_hints)
+        assert hints == {"x": int, "return": str}
+
+        # Test method type hints on instance
+        model = ModelWithHints()
+        assert get_type_hints(model.method_with_hints) == {"x": int, "return": str}