Explicitly annotate the possibility of GenericAlias

Despite describing the type of values, `GenericAlias` is not actually
a subclass of `type`.

Author: mthuurne

src/dataclass_binder/_impl.py

@@ -24,7 +24,7 @@
 from inspect import cleandoc, get_annotations, getmodule, getsource, isabstract
 from pathlib import Path
 from textwrap import dedent
-from types import MappingProxyType, ModuleType, NoneType, UnionType
+from types import GenericAlias, MappingProxyType, ModuleType, NoneType, UnionType
 from typing import TYPE_CHECKING, Any, BinaryIO, ClassVar, Generic, TypeVar, Union, cast, get_args, get_origin, overload
 from weakref import WeakKeyDictionary
 
@@ -37,7 +37,7 @@
 # Note: Actually 'field_type' can either be a type of a typing special form,
 #       but there is no way yet to annotate typing special forms.
 #       This is the source of a lot of the casts and suppressions in this function.
-def _collect_type(field_type: type, context: str) -> type | Binder[Any]:
+def _collect_type(field_type: type, context: str) -> type | GenericAlias | Binder[Any]:
     """
     Verify and streamline a type annotation.
 
@@ -215,7 +215,7 @@ class _ClassInfo(Generic[T]):
     _cache: ClassVar[MutableMapping[type[Any], _ClassInfo[Any]]] = WeakKeyDictionary()
 
     dataclass: type[T]
-    field_types: Mapping[str, type | Binder[Any]]
+    field_types: Mapping[str, type | GenericAlias | Binder[Any]]
     _field_docstrings: Mapping[str, str] | None = None
 
     @classmethod
@@ -225,7 +225,7 @@ def get(cls, dataclass: type[T]) -> _ClassInfo[T]:
         except KeyError:
             # Populate field_types *after* adding new instance to the cache to make sure
             # _collect_type() will find the given dataclass if it's accessed recursively.
-            field_types: dict[str, type | Binder[Any]] = {}
+            field_types: dict[str, type | GenericAlias | Binder[Any]] = {}
             info = cls(dataclass, field_types)
             cls._cache[dataclass] = info
             for field, field_type in _get_fields(dataclass):
@@ -371,7 +371,9 @@ def _bind_to_single_type(self, value: object, field_type: type, context: str) ->
 
         raise TypeError(f"Value for '{context}' has type '{type(value).__name__}', expected '{field_type.__name__}'")
 
-    def _bind_to_field(self, value: object, field_type: type | Binder[Any], instance: T | None, context: str) -> object:
+    def _bind_to_field(
+        self, value: object, field_type: type | GenericAlias | Binder[Any], instance: T | None, context: str
+    ) -> object:
         """
         Convert a TOML value to a field type which is possibly a union type.
 
@@ -884,7 +886,7 @@ def format_template(class_or_instance: Any) -> Iterator[str]:
     yield from Binder(class_or_instance).format_toml_template()
 
 
-def _format_value_for_type(field_type: type[Any]) -> str:
+def _format_value_for_type(field_type: GenericAlias | type[Any]) -> str:
     origin = get_origin(field_type)
     if origin is None:
         if field_type is str: