Add test for type resolution using generics and forward references

Author: AdrianSosic

tests/forwardrefs.py

@@ -0,0 +1,14 @@
+"""Class definitions using forward references."""
+
+from __future__ import annotations
+
+from typing import Generic, TypeVar
+
+from attrs import define
+
+T = TypeVar("T")
+
+
+@define
+class GenericClass(Generic[T]):
+    t: T

tests/test_generics.py

@@ -4,13 +4,15 @@
 import pytest
 from attrs import asdict, define
 
+import cattrs
 from cattrs import BaseConverter, Converter
 from cattrs._compat import Protocol
 from cattrs._generics import deep_copy_with
 from cattrs.errors import StructureHandlerNotFoundError
 from cattrs.gen._generics import generate_mapping
 
 from ._compat import Dict_origin, List_origin, is_py310_plus, is_py311_plus
+from .forwardrefs import GenericClass
 
 T = TypeVar("T")
 T2 = TypeVar("T2")
@@ -161,7 +163,7 @@ class TClass2(Generic[T]):
 
 
 def test_raises_if_no_generic_params_supplied(
-    converter: Union[Converter, BaseConverter]
+    converter: Union[Converter, BaseConverter],
 ):
     data = TClass(1, "a")
 
@@ -358,3 +360,9 @@ class GenericEntity(GenericProtocol[int]):
     assert generate_mapping(GenericEntity) == {"T": int}
 
     assert converter.structure({"a": 1}, GenericEntity) == GenericEntity(1)
+
+
+def test_generics_with_forward_refs():
+    """Type resolution works with forward references."""
+    converter = cattrs.Converter()
+    converter.unstructure(GenericClass(42), unstructure_as=GenericClass[int])