Fix #66: dataclass from Generic now serializes

.changelog/_unreleased.toml

@@ -1,3 +1,9 @@
+[[entries]]
+id = "693674ea-b2b2-4733-bce6-4d5bae59b164"
+type = "fix"
+description = "Fix #66: dataclasses inheriting from uninstantiated Generic did not get all their fields serialized"
+author = "@rhaps0dy"
+
 [[entries]]
 id = "ab7f2766-e6f5-4236-946d-bddedcd73433"
 type = "fix"

databind/src/databind/core/schema.py

@@ -199,6 +199,7 @@ class A(Generic[T]):
 
     # Collect the members from the dataclass and its base classes.
     queue = [hint]
+    seen: t.Set[type] = set()
     fields: t.Dict[str, Field] = {}
     while queue:
         hint = queue.pop(0)
@@ -244,11 +245,16 @@ class A(Generic[T]):
             # are overwritten by other fields.
             pass
 
-        # Continue with the base classes.
-        for base in hint.bases or hint.type.__bases__:
+        # Continue with the base classes. We iterate both hint.bases (which provides
+        # parameterized generic type info from __orig_bases__) and hint.type.__bases__
+        # (the actual base classes). This is necessary because when a class inherits from
+        # a Generic without parameterizing it (e.g. `class B(A)` where A is Generic[T]),
+        # hint.bases only contains Generic[T] and misses the actual parent dataclass A.
+        for base in (*hint.bases, *hint.type.__bases__):
             base_hint = TypeHint(base, source=hint.type).evaluate().parameterize(parameter_map)
             assert isinstance(base_hint, ClassTypeHint), f"nani? {base_hint}"
-            if dataclasses.is_dataclass(base_hint.type):
+            if dataclasses.is_dataclass(base_hint.type) and base_hint.type not in seen:
+                seen.add(base_hint.type)
                 queue.append(base_hint)
 
     return Schema(fields, t.cast("Constructor", dataclass_type), dataclass_type)

databind/src/databind/core/tests/schema_test.py

@@ -456,3 +456,27 @@ def test_parse_dataclass_with_forward_ref() -> None:
         ClassWithForwardRef,
         ClassWithForwardRef,
     )
+
+
+UnboundTypeVar = t.TypeVar("UnboundTypeVar")
+
+
+@dataclasses.dataclass
+class GenericClass(t.Generic[UnboundTypeVar]):
+    a_field: int
+
+
+@dataclasses.dataclass
+class InheritGeneric(GenericClass):  # type: ignore[type-arg]
+    b_field: str
+
+
+def test_schema_generic_dataclass() -> None:
+    """Regression test for #66: dataclasses inheriting from Generic with an uninstantiated TypeVar don't get their
+    parents' fields.
+    """
+    assert convert_dataclass_to_schema(InheritGeneric) == Schema(
+        {"a_field": Field(TypeHint(int), True), "b_field": Field(TypeHint(str), True)},
+        InheritGeneric,
+        InheritGeneric,
+    )

databind/src/databind/json/tests/converters_test.py

@@ -719,6 +719,34 @@ def of(cls, v: str) -> "MyCls":
     assert mapper.deserialize("MyCls", MyCls) == MyCls()
 
 
+UnboundTypeVar = t.TypeVar("UnboundTypeVar")
+
+
+@dataclasses.dataclass
+class GenericClass(t.Generic[UnboundTypeVar]):
+    a_field: int
+
+
+@dataclasses.dataclass
+class InheritGeneric(GenericClass):  # type: ignore[type-arg]
+    b_field: str
+
+
+@pytest.mark.parametrize("direction", (Direction.SERIALIZE, Direction.DESERIALIZE))
+def test_convert_generic_dataclass(direction: Direction) -> None:
+    """Regression test for #66: dataclasses inheriting from Generic with an uninstantiated TypeVar don't get their
+    parents' fields.
+    """
+    mapper = make_mapper([SchemaConverter(), PlainDatatypeConverter()])
+
+    if direction == Direction.SERIALIZE:
+        obj = InheritGeneric(2, "hi")
+        assert mapper.convert(direction, obj, InheritGeneric) == {"a_field": obj.a_field, "b_field": obj.b_field}
+    else:
+        obj = InheritGeneric(4, "something")
+        assert mapper.convert(direction, {"a_field": obj.a_field, "b_field": obj.b_field}, InheritGeneric) == obj
+
+
 def test_extra_keys_on_subclass_creates_own_settings() -> None:
     """Regression test: ExtraKeys() applied to a subclass must create its own __databind_settings__,
     not append to the parent's list via MRO traversal."""