Fix bug with repeated use of the sane generic dataclass

See lovasoa#172 (comment)

Author: dairiki

marshmallow_dataclass/__init__.py

@@ -46,6 +46,8 @@ class User:
     Any,
     Callable,
     Dict,
+    Generic,
+    Hashable,
     List,
     Mapping,
     NewType as typing_NewType,
@@ -367,6 +369,43 @@ def _dataclass_fields(clazz: type) -> Tuple[dataclasses.Field, ...]:
     return dataclasses.fields(clazz)
 
 
+class InvalidStateError(Exception):
+    """Raised when an operation is performed on a future that is not
+    allowed in the current state.
+    """
+
+
+class _Future(Generic[_U]):
+    """The _Future class allows deferred access to a result that is not
+    yet available.
+    """
+
+    _done: bool
+    _result: _U
+
+    def __init__(self) -> None:
+        self._done = False
+
+    def done(self) -> bool:
+        """Return ``True`` if the value is available"""
+        return self._done
+
+    def result(self) -> _U:
+        """Return the deferred value.
+
+        Raises ``InvalidStateError`` if the value has not been set.
+        """
+        if self.done():
+            return self._result
+        raise InvalidStateError("result has not been set")
+
+    def set_result(self, result: _U) -> None:
+        if self.done():
+            raise InvalidStateError("result has already been set")
+        self._result = result
+        self._done = True
+
+
 @lru_cache(maxsize=MAX_CLASS_SCHEMA_CACHE_SIZE)
 def _internal_class_schema(
     clazz: type,
@@ -377,7 +416,8 @@ def _internal_class_schema(
     # generic aliases do not have a __name__ prior python 3.10
     _name = getattr(clazz, "__name__", repr(clazz))
 
-    _RECURSION_GUARD.seen_classes[clazz] = _name
+    future: _Future[Type[marshmallow.Schema]] = _Future()
+    _RECURSION_GUARD.seen_classes[clazz] = future
     try:
         fields = _dataclass_fields(clazz)
     except TypeError:  # Not a dataclass
@@ -430,8 +470,11 @@ def _internal_class_schema(
         if field.init
     )
 
-    schema_class = type(_name, (_base_schema(clazz, base_schema),), attributes)
-    return cast(Type[marshmallow.Schema], schema_class)
+    schema_class: Type[marshmallow.Schema] = type(
+        _name, (_base_schema(clazz, base_schema),), attributes
+    )
+    future.set_result(schema_class)
+    return schema_class
 
 
 def _field_by_type(
@@ -769,17 +812,18 @@ def field_for_schema(
 
     # Nested marshmallow dataclass
     # it would be just a class name instead of actual schema util the schema is not ready yet
-    nested_schema = getattr(typ, "Schema", None)
-
-    # Nested dataclasses
-    forward_reference = getattr(typ, "__forward_arg__", None)
-
-    nested = (
-        nested_schema
-        or forward_reference
-        or _RECURSION_GUARD.seen_classes.get(typ)
-        or _internal_class_schema(typ, base_schema, typ_frame, generic_params_to_args)
-    )
+    if typ in _RECURSION_GUARD.seen_classes:
+        nested = _RECURSION_GUARD.seen_classes[typ].result
+    elif hasattr(typ, "Schema"):
+        nested = typ.Schema
+    elif hasattr(typ, "__forward_arg__"):
+        # FIXME: is this still used?
+        nested = typ.__forward_arg__
+    else:
+        assert isinstance(typ, Hashable)
+        nested = _internal_class_schema(
+            typ, base_schema, typ_frame, generic_params_to_args
+        )
 
     return marshmallow.fields.Nested(nested, **metadata)
 

tests/test_class_schema.py

@@ -462,11 +462,11 @@ class BB(typing.Generic[T]):
 
         @dataclasses.dataclass
         class Nested:
+            y: BB[AA]
             x: BB[float]
             z: BB[float]
             # if y is the first field in this class, deserialisation will fail.
             # see https://github.com/lovasoa/marshmallow_dataclass/pull/172#issuecomment-1334024027
-            y: BB[AA]
 
         schema_nested = class_schema(Nested)()
         self.assertEqual(