Fix serialization of dataclass inheriting from abc.ABC and using __slots__

Author: ijl

src/serialize/serializer.rs

@@ -257,7 +257,10 @@ impl<'p> Serialize for PyObjectSerializer {
                     err!(RECURSION_LIMIT_REACHED)
                 }
                 let dict = ffi!(PyObject_GetAttr(self.ptr, DICT_STR));
-                if unlikely!(dict.is_null()) {
+                let ob_type = ob_type!(self.ptr);
+                if unlikely!(
+                    dict.is_null() || ffi!(PyDict_Contains((*ob_type).tp_dict, SLOTS_STR)) == 1
+                ) {
                     unsafe { pyo3::ffi::PyErr_Clear() };
                     DataclassFallbackSerializer::new(
                         self.ptr,

src/typeref.rs

@@ -53,6 +53,7 @@ pub static mut EMPTY_UNICODE: *mut PyObject = 0 as *mut PyObject;
 pub static mut DST_STR: *mut PyObject = 0 as *mut PyObject;
 pub static mut DICT_STR: *mut PyObject = 0 as *mut PyObject;
 pub static mut DATACLASS_FIELDS_STR: *mut PyObject = 0 as *mut PyObject;
+pub static mut SLOTS_STR: *mut PyObject = 0 as *mut PyObject;
 pub static mut FIELD_TYPE_STR: *mut PyObject = 0 as *mut PyObject;
 pub static mut ARRAY_STRUCT_STR: *mut PyObject = 0 as *mut PyObject;
 pub static mut DTYPE_STR: *mut PyObject = 0 as *mut PyObject;
@@ -122,6 +123,7 @@ pub fn init_typerefs() {
         DICT_STR = PyUnicode_InternFromString("__dict__\0".as_ptr() as *const c_char);
         DATACLASS_FIELDS_STR =
             PyUnicode_InternFromString("__dataclass_fields__\0".as_ptr() as *const c_char);
+        SLOTS_STR = PyUnicode_InternFromString("__slots__\0".as_ptr() as *const c_char);
         FIELD_TYPE_STR = PyUnicode_InternFromString("_field_type\0".as_ptr() as *const c_char);
         ARRAY_STRUCT_STR =
             pyo3::ffi::PyUnicode_InternFromString("__array_struct__\0".as_ptr() as *const c_char);

test/test_dataclass.py

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
+import abc
 import unittest
 import uuid
 from dataclasses import InitVar, asdict, dataclass, field
@@ -95,6 +96,23 @@ def __post_init__(self, a: str, b: str):
         self.ab = f"{a} {b}"
 
 
+class AbstractBase(abc.ABC):
+    @abc.abstractmethod
+    def key(self):
+        raise NotImplementedError
+
+
+@dataclass(frozen=True)
+class ConcreteAbc(AbstractBase):
+
+    __slots__ = ("attr",)
+
+    attr: float
+
+    def key(self):
+        return "dkjf"
+
+
 class DataclassTests(unittest.TestCase):
     def test_dataclass(self):
         """
@@ -291,3 +309,9 @@ def default(obj):
             orjson.dumps(obj, option=orjson.OPT_PASSTHROUGH_DATACLASS, default=default),
             b'{"name":"a","number":1}',
         )
+
+
+class AbstractDataclassTests(unittest.TestCase):
+    def test_dataclass_abc(self):
+        obj = ConcreteAbc(1.0)
+        self.assertEqual(orjson.dumps(obj), b'{"attr":1.0}')