GenConverter: fix issue with unstructuring attrs classes with generic…

… fields

HISTORY.rst

@@ -4,6 +4,8 @@ History
 
 1.5.0 (UNRELEASED)
 ------------------
+* Fix an issue with ``GenConverter`` unstructuring ``attrs`` classes and dataclasses with generic fields.
+  (`#65 </~https://github.com/Tinche/cattrs/issues/65>`_)
 
 1.4.0 (2021-03-21)
 ------------------

src/cattr/_compat.py

@@ -48,6 +48,11 @@ def has(cls):
     )
 
 
+def has_with_generic(cls):
+    """Test whether the class if a normal or generic attrs or dataclass."""
+    return has(cls) or has(get_origin(cls))
+
+
 def fields(type):
     try:
         return type.__attrs_attrs__

src/cattr/converters.py

@@ -17,6 +17,7 @@
     is_annotated,
     has,
     fields,
+    has_with_generic,
 )
 from .disambiguators import create_uniq_field_dis_func
 from .dispatch import MultiStrategyDispatch
@@ -490,7 +491,7 @@ def __init__(
             self._unstructure_func.register_func_list(
                 [
                     (
-                        has,
+                        has_with_generic,
                         self.gen_unstructure_attrs_fromdict,
                         True,
                     ),
@@ -541,6 +542,9 @@ def gen_structure_annotated(self, type):
         return h
 
     def gen_unstructure_attrs_fromdict(self, cl: Type[T]) -> Dict[str, Any]:
+        origin = get_origin(cl)
+        if origin is not None:
+            cl = origin
         attribs = fields(cl)
         if any(isinstance(a.type, str) for a in attribs):
             # PEP 563 annotations - need to be resolved.

tests/test_generics.py

@@ -3,7 +3,7 @@
 import pytest
 from attr import asdict, attrs
 
-from cattr import Converter
+from cattr import Converter, GenConverter
 
 T = TypeVar("T")
 T2 = TypeVar("T2")
@@ -83,3 +83,29 @@ def test_raises_if_no_generic_params_supplied(converter):
         match="Unsupported type: ~T. Register a structure hook for it.",
     ):
         converter.structure(asdict(data), TClass)
+
+
+def test_unstructure_generic_attrs():
+    c = GenConverter()
+
+    @attrs(auto_attribs=True)
+    class Inner(Generic[T]):
+        a: T
+
+    @attrs(auto_attribs=True)
+    class Outer:
+        inner: Inner[int]
+
+    initial = Outer(Inner(1))
+    raw = c.unstructure(initial)
+
+    assert raw == {"inner": {"a": 1}}
+
+    new = c.structure(raw, Outer)
+    assert initial == new
+
+    @attrs(auto_attribs=True)
+    class OuterStr:
+        inner: Inner[str]
+
+    assert c.structure(raw, OuterStr) == OuterStr(Inner("1"))