Fix ForwardRef issue in Python 3.9.8 (#280)

apischema/typing.py

@@ -7,12 +7,12 @@
     Any,
     Callable,
     Collection,
+    Dict,
     Generic,
     Set,
     Tuple,
     Type,
     TypeVar,
-    _eval_type,
 )
 
 
@@ -152,44 +152,32 @@ def generic_mro(tp):
     return tuple(result.get(sub_cls, sub_cls) for sub_cls in cls.__mro__)
 
 
-def _class_annotations(cls, globalns, localns):
-    hints = {}
-    if globalns is None:
-        base_globals = sys.modules[cls.__module__].__dict__
-    else:
-        base_globals = globalns
-    for name, value in cls.__dict__.get("__annotations__", {}).items():
-        if value is None:
-            value = type(None)
-        if isinstance(value, str):
-            value = ForwardRef(value, is_argument=False)
-        hints[name] = _eval_type(value, base_globals, localns)
-    return hints
-
+def resolve_type_hints(obj: Any) -> Dict[str, Any]:
+    """Wrap get_type_hints to resolve type vars in case of generic inheritance.
 
-def get_type_hints2(obj, globalns=None, localns=None):  # type: ignore
-    if isinstance(obj, type) or isinstance(get_origin(obj), type):
-        hints = {}
+    `obj` can also be a parametrized generic class."""
+    origin_or_obj = get_origin(obj) or obj
+    hints = get_type_hints(origin_or_obj, include_extras=True)
+    if isinstance(origin_or_obj, type):
         for base in reversed(generic_mro(obj)):
-            origin = get_origin(base)
-            if hasattr(origin, "__orig_bases__"):
-                parameters = _collect_type_vars(origin.__orig_bases__)
-                substitution = dict(zip(parameters, get_args(base)))
-                annotations = _class_annotations(get_origin(base), globalns, localns)
-                for name, tp in annotations.items():
-                    if isinstance(tp, TypeVar):
-                        hints[name] = substitution.get(tp, tp)
-                    elif getattr(tp, "__parameters__", ()):
-                        hints[name] = tp[
-                            tuple(substitution.get(p, p) for p in tp.__parameters__)
+            base_origin = get_origin(base)
+            if base_origin is not None and getattr(base_origin, "__parameters__", ()):  # type: ignore
+                substitution = dict(zip(base_origin.__parameters__, get_args(base)))
+                base_annotations = getattr(base_origin, "__dict__", {}).get(
+                    "__annotations__", {}
+                )
+                for name, hint in get_type_hints(base_origin).items():
+                    if name not in base_annotations:
+                        continue
+                    if isinstance(hint, TypeVar):
+                        hints[name] = substitution.get(hint, hint)
+                    elif getattr(hint, "__parameters__", ()):
+                        hints[name] = hint[
+                            tuple(substitution.get(p, p) for p in hint.__parameters__)
                         ]
                     else:
-                        hints[name] = tp
-            else:
-                hints.update(_class_annotations(base, globalns, localns))
-        return hints
-    else:
-        return get_type_hints(obj, globalns, localns, include_extras=True)
+                        hints[name] = hint
+    return hints
 
 
 _T = TypeVar("_T")

apischema/visitor.py

@@ -31,31 +31,27 @@
     get_args,
     get_origin,
     get_type_hints,
-    get_type_hints2,
     is_annotated,
     is_literal,
     is_named_tuple,
     is_type_var,
     is_typed_dict,
     required_keys,
+    resolve_type_hints,
 )
 from apischema.utils import PREFIX, get_origin_or_type, has_type_vars, is_dataclass
 
 TUPLE_TYPE = get_origin(Tuple[Any])
 
 
-def type_hints_cache(obj) -> Mapping[str, AnyType]:
-    return get_type_hints2(obj)
-
-
 def dataclass_types_and_fields(
     tp: AnyType,
 ) -> Tuple[Mapping[str, AnyType], Sequence[Field], Sequence[Field]]:
     from apischema.metadata.keys import INIT_VAR_METADATA
 
     cls = get_origin_or_type(tp)
     assert is_dataclass(cls)
-    types = get_type_hints2(tp)
+    types = resolve_type_hints(tp)
     fields, init_fields = [], []
     for field in getattr(cls, _FIELDS).values():
         assert isinstance(field, Field)
@@ -188,7 +184,7 @@ def visit(self, tp: AnyType) -> Result:
             # NamedTuple
             if is_named_tuple(origin):
                 if hasattr(origin, "__annotations__"):
-                    types = type_hints_cache(origin)
+                    types = resolve_type_hints(origin)
                 elif hasattr(origin, "__field_types"):  # pragma: no cover
                     types = origin.__field_types  # type: ignore
                 else:  # pragma: no cover
@@ -200,7 +196,7 @@ def visit(self, tp: AnyType) -> Result:
             return self.literal(origin.__values__)  # type: ignore
         if is_typed_dict(origin):
             return self.typed_dict(
-                origin, type_hints_cache(origin), required_keys(origin)
+                origin, resolve_type_hints(origin), required_keys(origin)
             )
         if is_type_var(origin):
             if origin.__constraints__:

tests/test_typing.py

@@ -3,7 +3,12 @@
 
 from pytest import mark
 
-from apischema.typing import _TypedDictMeta, generic_mro, get_type_hints2, required_keys
+from apischema.typing import (
+    _TypedDictMeta,
+    generic_mro,
+    required_keys,
+    resolve_type_hints,
+)
 
 T = TypeVar("T")
 U = TypeVar("U")
@@ -44,8 +49,8 @@ def test_generic_mro(tp, result, _):
 
 
 @mark.parametrize("tp, _, result", test_cases)
-def test_get_type_hints2(tp, _, result):
-    assert get_type_hints2(tp) == result
+def test_resolve_type_hints(tp, _, result):
+    assert resolve_type_hints(tp) == result
 
 
 def test_required_keys():