Fix bug handling default values for frozen & slotted dataclasses

Previously there was a bug where dataclasses or attrs classes with
`slots=True, frozen=True` wouldn't be able to properly use default
values for optional fields.

msgspec/_core.c

@@ -8049,7 +8049,7 @@ DataclassInfo_post_decode(DataclassInfo *self, PyObject *obj, PathNode *path) {
  default_value = CALL_NO_ARGS(default_value);
  if (default_value == NULL) return -1;
  }
- int status = PyObject_SetAttr(obj, name, default_value);
+ int status = PyObject_GenericSetAttr(obj, name, default_value);
  if (is_factory) {
  Py_DECREF(default_value);
  }

tests/test_common.py

@@ -2694,16 +2694,17 @@ class Example:
  ):
  dec.decode(proto.encode({"a": "bad"}))
 
+ @pytest.mark.parametrize("frozen", [False, True])
  @pytest.mark.parametrize("slots", [False, True])
- def test_decode_dataclass_defaults(self, proto, slots):
+ def test_decode_dataclass_defaults(self, proto, frozen, slots):
  if slots:
  if not PY310:
  pytest.skip(reason="Python 3.10+ required")
  kws = {"slots": True}
  else:
  kws = {}
 
- @dataclass(**kws)
+ @dataclass(frozen=frozen, **kws)
  class Example:
  a: int
  b: int
@@ -2904,9 +2905,10 @@ class Example:
  ):
  dec.decode(proto.encode({"a": "bad"}))
 
+ @pytest.mark.parametrize("frozen", [False, True])
  @pytest.mark.parametrize("slots", [False, True])
- def test_decode_attrs_defaults(self, proto, slots):
- @attrs.define(slots=slots)
+ def test_decode_attrs_defaults(self, proto, frozen, slots):
+ @attrs.define(frozen=frozen, slots=slots)
  class Example:
  a: int
  b: int
@@ -2916,9 +2918,10 @@ class Example:
 
  dec = proto.Decoder(Example)
  for args in [(1, 2), (1, 2, 3), (1, 2, 3, 4), (1, 2, 3, 4, 5)]:
- msg = Example(*args)
+ sol = Example(*args)
+ msg = dict(zip("abcde", args))
  res = dec.decode(proto.encode(msg))
- assert res == msg
+ assert res == sol
 
  # Missing fields error
  with pytest.raises(ValidationError, match="missing required field `a`"):

tests/test_convert.py

@@ -1388,17 +1388,18 @@ class Ex:
 
  assert convert(msg, Ex, from_attributes=True) == Ex(1)
 
+ @pytest.mark.parametrize("frozen", [False, True])
  @pytest.mark.parametrize("slots", [False, True])
  @mapcls_and_from_attributes
- def test_dataclass_defaults(self, slots, mapcls, from_attributes):
+ def test_dataclass_defaults(self, frozen, slots, mapcls, from_attributes):
  if slots:
  if not PY310:
  pytest.skip(reason="Python 3.10+ required")
  kws = {"slots": True}
  else:
  kws = {}
 
- @dataclass(**kws)
+ @dataclass(frozen=frozen, **kws)
  class Example:
  a: int
  b: int
@@ -1557,10 +1558,11 @@ class Ex:
 
  assert convert(msg, Ex, from_attributes=True) == Ex(1)
 
+ @pytest.mark.parametrize("frozen", [False, True])
  @pytest.mark.parametrize("slots", [False, True])
  @mapcls_and_from_attributes
- def test_attrs_defaults(self, slots, mapcls, from_attributes):
- @attrs.define(slots=slots)
+ def test_attrs_defaults(self, frozen, slots, mapcls, from_attributes):
+ @attrs.define(frozen=frozen, slots=slots)
  class Example:
  a: int
  b: int