Add support for attrs factories taking self.

Author: desert

src/desert/_make.py

@@ -319,16 +319,16 @@ def _get_field_default(field: t.Union[dataclasses.Field, attr.Attribute]):
     """
     if isinstance(field, dataclasses.Field):
         if field.default_factory != dataclasses.MISSING:
-            return field.default_factory
-        elif field.default is dataclasses.MISSING:
+            return dataclasses.MISSING
+        if field.default is dataclasses.MISSING:
             return marshmallow.missing
         return field.default
     elif isinstance(field, attr.Attribute):
         if field.default == attr.NOTHING:
             return marshmallow.missing
         if isinstance(field.default, attr.Factory):
             if field.default.takes_self:
-                raise NotImplementedError("Takes self not implemented")
+                return attr.NOTHING
             return field.default.factory
         return field.default
     else:

tests/test_make.py

@@ -414,3 +414,19 @@ def test_only_raises():
 
     with pytest.raises(ValueError):
         desert._make.only([1, 2])
+
+
+def test_takes_self():
+    """Attrs default factories are constructed after instance creation."""
+
+    @attr.s
+    class C:
+        x: int = attr.ib()
+        y: int = attr.ib()
+
+        @y.default
+        def _(self):
+            return self.x + 1
+
+    schema = desert.schema(C)
+    assert schema.load({"x": 1}) == C(x=1, y=2)