fix: reconstruct dataclasses with derived fields

CHANGELOG.md

@@ -9,6 +9,14 @@ adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 FIXED
 
+- Dataclasses with `init=False` fields now reconstruct as their declared type
+instead of falling back to a raw dictionary when their generated constructor
+cannot accept those fields. Handwritten constructors continue to receive
+serialized non-init fields they accept as keywords, including through
+`**kwargs`. Other non-init fields use defaults, default factories, or
+`__post_init__` and may reset previously recorded values. Reconstruction must
+be deterministic for replay; use an explicit `from_json()` hook to preserve
+recorded state that the constructor cannot accept.
 - Single-instance `purge_orchestration()` requests now explicitly target
 orchestrations rather than entities in both synchronous and asynchronous clients.
 - Timer callbacks no longer schedule additional long-timer chunks, retry

durabletask/serialization.py

@@ -144,6 +144,16 @@ class JsonDataConverter(DataConverter):
     keeps the core SDK permissive; a stricter, validating converter can be
     supplied for callers who want coercion failures to surface as errors.
 
+    Dataclass fields marked ``init=False`` are passed to a handwritten
+    initializer when it accepts them as keywords, including through
+    ``**kwargs``. Otherwise they are omitted: generated initializers use
+    defaults and default factories, and ``__post_init__`` can recompute derived
+    values. Previously recorded non-init values may therefore be reset, or
+    remain unset if the class initializes them externally. Constructors,
+    default factories, and ``__post_init__`` must behave deterministically for
+    replay. Define an explicit ``from_json()`` hook to preserve recorded
+    non-init state that the initializer cannot accept.
+
     > [!NOTE]
     > Type-directed reconstruction recurses through dataclass fields,
     > ``list``/``Sequence``, ``dict``/``Mapping`` values, ``tuple`` elements,
@@ -494,6 +504,32 @@ def _coerce_generic(value: Any, expected_type: Any, origin: Any,
     return value
 
 
+@functools.lru_cache(maxsize=256)
+def _dataclass_init_keywords(initializer: Any) -> tuple[frozenset[str] | None, str | None]:
+    """Return keyword names and a potentially reserved receiver name.
+
+    A None keyword set represents **kwargs or an unavailable signature.
+    The caller accounts for receiver binding when using the reserved name.
+    """
+    try:
+        parameters = list(inspect.signature(initializer, follow_wrapped=False).parameters.values())
+    except (TypeError, ValueError):
+        # Preserve the legacy keyword-passing behavior when inspection fails.
+        return None, None
+    receiver = None
+    # Positional-only receiver names remain available as keys in **kwargs.
+    if parameters and parameters[0].kind is inspect.Parameter.POSITIONAL_OR_KEYWORD:
+        receiver = parameters[0].name
+    if any(p.kind is inspect.Parameter.VAR_KEYWORD for p in parameters):
+        return None, receiver
+    keywords = frozenset(
+        p.name for p in parameters
+        if p.kind in (inspect.Parameter.POSITIONAL_OR_KEYWORD,
+                      inspect.Parameter.KEYWORD_ONLY)
+    )
+    return keywords, receiver
+
+
 def _build_dataclass(cls: Any, data: dict[str, Any],
                      converter: DataConverter | None = None) -> Any:
     """Construct a dataclass from its dict payload, recursing into typed fields."""
@@ -506,6 +542,22 @@ def _build_dataclass(cls: Any, data: dict[str, Any],
     for field in dataclasses.fields(cls):
         if field.name not in data:
             continue
+        if not field.init:
+            initializer = cls.__init__
+            try:
+                init_keywords, receiver = _dataclass_init_keywords(initializer)
+            except TypeError:
+                # Unhashable initializer callables cannot use the cache.
+                init_keywords, receiver = None, None
+            if init_keywords is not None and field.name not in init_keywords:
+                continue
+            if (field.name == receiver
+                    and (inspect.isfunction(initializer) or inspect.ismethoddescriptor(initializer))
+                    and not isinstance(inspect.getattr_static(cls, "__init__"), staticmethod)):
+                # Normal instance initializers already receive this argument.
+                # Bound classmethods omit it from their inspected signature;
+                # staticmethods have no implicit receiver.
+                continue
         # ``get_type_hints`` on Python 3.10 does not deep-resolve forward
         # references nested inside container args (e.g. the ``"TreeNode"`` in
         # ``list["TreeNode"]`` on a self-referential dataclass), leaving a bare

tests/durabletask/test_data_converter.py

@@ -3,11 +3,17 @@
 
 """Tests for the DataConverter abstraction and the default JsonDataConverter."""
 
+import inspect
 import json
 import logging
-from dataclasses import dataclass
+from dataclasses import dataclass, field
+from functools import wraps
 from typing import Any
+from unittest.mock import patch
 
+import pytest
+
+from durabletask.internal.entity_state_shim import StateShim
 from durabletask.serialization import (
     DEFAULT_DATA_CONVERTER,
     DataConverter,
@@ -21,6 +27,284 @@ class Order:
     quantity: int
 
 
+@dataclass(frozen=True)
+class PricedOrder:
+    quantity: int
+    unit_price: int
+    total: int = field(init=False)
+
+    def __post_init__(self):
+        object.__setattr__(self, "total", self.quantity * self.unit_price)
+
+
+@dataclass
+class Shipment:
+    order: PricedOrder
+
+
+def test_round_trip_dataclass_with_derived_field():
+    converter = JsonDataConverter()
+    order = PricedOrder(3, 10)
+    encoded = converter.serialize(order)
+    assert json.loads(encoded) == {"quantity": 3, "unit_price": 10, "total": 30}
+    assert converter.deserialize(encoded, PricedOrder) == order
+
+
+def test_coerce_dataclass_recomputes_derived_field():
+    converter = JsonDataConverter()
+    result = converter.coerce({"quantity": 3, "unit_price": 10, "total": 999}, PricedOrder)
+    assert result == PricedOrder(3, 10)
+    assert result.total == 30
+
+
+def test_round_trip_nested_dataclass_with_derived_field():
+    converter = JsonDataConverter()
+    shipment = Shipment(PricedOrder(3, 10))
+    assert converter.deserialize(converter.serialize(shipment), Shipment) == shipment
+
+
+@dataclass
+class CounterState:
+    name: str
+    counter: int = field(init=False, default=0)
+
+    def __init__(self, name: str, counter: int = 0):
+        self.name = name
+        self.counter = counter
+
+
+@dataclass
+class KeywordCounterState:
+    name: str
+    counter: int = field(init=False, default=0)
+
+    def __init__(self, name: str, *, counter: int = 0):
+        self.name = name
+        self.counter = counter
+
+
+@dataclass
+class KwargsCounterState:
+    name: str
+    counter: int = field(init=False, default=0)
+
+    def __init__(self, name: str, **kwargs):
+        self.name = name
+        self.counter = kwargs.get("counter", 0)
+
+
+@pytest.mark.parametrize("state_type", [CounterState, KeywordCounterState, KwargsCounterState])
+def test_non_init_field_preserved_by_custom_constructor(state_type):
+    converter = JsonDataConverter()
+    original = state_type("persisted", counter=42)
+    encoded = converter.serialize(original)
+    restored = converter.deserialize(encoded, state_type)
+    assert restored == original
+    assert restored.counter == 42
+
+    state = StateShim(encoded, converter, is_serialized=True)
+    restored_state = state.get_state(state_type)
+    assert restored_state.counter == 42
+    state.set_state(restored_state)
+    assert json.loads(state.encode_state()) == {"name": "persisted", "counter": 42}
+
+
+@pytest.mark.parametrize("accept_kwargs", [False, True])
+def test_non_init_field_preserved_by_decorated_initializer(accept_kwargs):
+    @dataclass
+    class DecoratedCounterState:
+        name: str
+        counter: int = field(init=False, default=0)
+
+    generated_init = DecoratedCounterState.__init__
+    if accept_kwargs:
+        @wraps(generated_init)
+        def restore_counter(self, *args, **kwargs):
+            counter = kwargs.pop("counter", 0)
+            generated_init(self, *args, **kwargs)
+            self.counter = counter
+    else:
+        @wraps(generated_init)
+        def restore_counter(self, *args, counter=0, **kwargs):
+            generated_init(self, *args, **kwargs)
+            self.counter = counter
+    DecoratedCounterState.__init__ = restore_counter
+
+    converter = JsonDataConverter()
+    original = DecoratedCounterState("persisted", counter=42)
+    encoded = converter.serialize(original)
+    assert converter.deserialize(encoded, DecoratedCounterState).counter == 42
+
+    state = StateShim(encoded, converter, is_serialized=True)
+    restored = state.get_state(DecoratedCounterState)
+    assert restored.counter == 42
+    state.set_state(restored)
+    assert json.loads(state.encode_state()) == {"name": "persisted", "counter": 42}
+
+
+@pytest.mark.parametrize("accept_kwargs", [False, True])
+def test_non_init_custom_constructor_field_is_recursively_coerced(accept_kwargs):
+    @dataclass
+    class CustomShipment:
+        order: Order = field(init=False)
+
+    if accept_kwargs:
+        def initializer(self, **kwargs):
+            self.order = kwargs["order"]
+    else:
+        def initializer(self, *, order):
+            self.order = order
+    CustomShipment.__init__ = initializer
+
+    converter = JsonDataConverter()
+    restored = converter.deserialize('{"order": {"item": "book", "quantity": 42}}', CustomShipment)
+    assert isinstance(restored, CustomShipment)
+    assert restored.order == Order("book", 42)
+
+
+def test_non_init_positional_only_constructor_parameter_is_omitted():
+    @dataclass
+    class PositionalCounter:
+        counter: int = field(init=False)
+
+        def __init__(self, counter=0, /):
+            self.counter = counter
+
+    restored = JsonDataConverter().deserialize('{"counter": 42}', PositionalCounter)
+    assert isinstance(restored, PositionalCounter)
+    assert restored.counter == 0
+
+
+@pytest.mark.parametrize("method_type", [classmethod, staticmethod])
+def test_non_init_field_preserved_by_descriptor_initializer(method_type):
+    @dataclass
+    class DescriptorCounter:
+        counter: int = field(init=False, default=0)
+
+    if method_type is classmethod:
+        def initializer(cls, counter=0):
+            cls.counter = counter
+    else:
+        def initializer(counter=0):
+            DescriptorCounter.counter = counter
+    DescriptorCounter.__init__ = method_type(initializer)
+
+    converter = JsonDataConverter()
+    encoded = converter.serialize(DescriptorCounter(counter=42))
+    DescriptorCounter.counter = 0
+    restored = converter.deserialize(encoded, DescriptorCounter)
+    assert isinstance(restored, DescriptorCounter)
+    assert restored.counter == 42
+
+
+def test_non_init_field_matching_receiver_name_is_omitted():
+    @dataclass
+    class ReceiverCounter:
+        counter: int = field(init=False)
+
+        def __init__(counter):
+            counter.counter = 7
+
+    restored = JsonDataConverter().deserialize('{"counter": 42}', ReceiverCounter)
+    assert isinstance(restored, ReceiverCounter)
+    assert restored.counter == 7
+
+
+def test_positional_only_receiver_name_can_be_passed_through_kwargs():
+    @dataclass
+    class PositionalReceiver:
+        self: int = field(init=False, default=0)
+
+        def __init__(self, /, **kwargs):
+            self.self = kwargs.get("self", 0)
+
+    converter = JsonDataConverter()
+    encoded = converter.serialize(PositionalReceiver(**{"self": 42}))
+    restored = converter.deserialize(encoded, PositionalReceiver)
+    assert isinstance(restored, PositionalReceiver)
+    assert restored.self == 42
+
+
+@pytest.mark.parametrize("hashable", [True, False])
+def test_non_init_field_preserved_by_callable_initializer(hashable):
+    @dataclass
+    class CallableCounter:
+        counter: int = field(init=False, default=0)
+
+    class Initializer:
+        def __call__(self, counter=0):
+            CallableCounter.counter = counter
+
+    if not hashable:
+        Initializer.__hash__ = None
+    CallableCounter.__init__ = Initializer()
+
+    converter = JsonDataConverter()
+    encoded = converter.serialize(CallableCounter(counter=42))
+    CallableCounter.counter = 0
+    restored = converter.deserialize(encoded, CallableCounter)
+    assert isinstance(restored, CallableCounter)
+    assert restored.counter == 42
+
+
+@pytest.mark.parametrize("error_type", [TypeError, ValueError])
+def test_non_init_fields_retained_when_constructor_signature_unavailable(error_type):
+    @dataclass
+    class UninspectableCounter:
+        counter: int = field(init=False)
+
+        def __init__(self, counter=0):
+            self.counter = counter
+
+    with patch("durabletask.serialization.inspect.signature", side_effect=error_type):
+        restored = JsonDataConverter().deserialize('{"counter": 42}', UninspectableCounter)
+    assert isinstance(restored, UninspectableCounter)
+    assert restored.counter == 42
+
+
+def test_dataclass_constructor_typeerror_is_not_retried():
+    calls = []
+
+    @dataclass
+    class FailingCounter:
+        counter: int = field(init=False)
+
+        def __init__(self, counter=0):
+            calls.append(counter)
+            raise TypeError("failure inside user constructor")
+
+    restored = JsonDataConverter().deserialize('{"counter": 42}', FailingCounter)
+    assert restored == {"counter": 42}
+    assert calls == [42]
+
+
+def test_ordinary_dataclass_skips_constructor_signature_inspection():
+    with patch("durabletask.serialization.inspect.signature", side_effect=AssertionError("unexpected inspection")):
+        restored = JsonDataConverter().deserialize('{"item": "book", "quantity": 42}', Order)
+    assert restored == Order("book", 42)
+
+
+def test_constructor_signature_cached_by_initializer():
+    @dataclass
+    class SharedInitializer:
+        counter: int = field(init=False)
+
+        def __init__(self, counter=0):
+            self.counter = counter
+
+    @dataclass(init=False)
+    class InheritedInitializer(SharedInitializer):
+        pass
+
+    converter = JsonDataConverter()
+    with patch("durabletask.serialization.inspect.signature", wraps=inspect.signature) as signature:
+        for cls in (SharedInitializer, InheritedInitializer, SharedInitializer):
+            restored = converter.deserialize('{"counter": 42}', cls)
+            assert isinstance(restored, cls)
+            assert restored.counter == 42
+    signature.assert_called_once_with(SharedInitializer.__init__, follow_wrapped=False)
+
+
 # ----- JsonDataConverter -----