First cut

pep-0681.rst

@@ -203,6 +203,7 @@ customization of default behaviors:
       eq_default: bool = True,
       order_default: bool = False,
       kw_only_default: bool = False,
+      transform_descriptor_types: bool = False,
       field_descriptors: tuple[type | Callable[..., Any], ...] = (),
   ) -> Callable[[_T], _T]: ...
 
@@ -218,6 +219,10 @@ customization of default behaviors:
   assumed to be True or False if it is omitted by the caller. If not
   specified, ``kw_only_default`` will default to False (the default
   assumption for dataclass).
+* ``transform_descriptor_types`` indicates whether, for fields whose
+  annotated types are descriptors, the corresponding parameter in the
+  synthesized ``__init__`` method should be the descriptor's setter
+  parameter type. If False, the descriptor type will be used.
 * ``field_descriptors`` specifies a static list of supported classes
   that describe fields. Some libraries also supply functions to
   allocate instances of field descriptors, and those functions may
@@ -326,6 +331,31 @@ Metaclass example
       id: int
       name: str
 
+``transform_descriptor_types`` example
+``````````````````````````````````````
+
+Because ``transform_descriptor_types`` is set to ``True``, the
+``target`` parameter on the synthesized ``__init__`` method will be of
+type ``float`` instead of ``Descriptor``.
+
+.. code-block:: python
+
+  class Descriptor:
+      def __get__(self, instance: object, owner: Any) -> int:
+            ...
+
+      # The setter and getter can have different types (asymmetric).
+      # The setter's value type is used for the __init__ parameter.
+      # The getter's return type is ignored.
+      def __set__(self, instance: object, value: float):
+          ...
+
+  class CustomerModel(
+      ModelBase,
+      transform_descriptor_types=True
+  ):
+      target: Descriptor
+
 
 Field descriptors
 -----------------
@@ -449,6 +479,7 @@ For example:
     "eq_default": True,
     "order_default": False,
     "kw_only_default": False,
+    "transform_descriptor_types": False,
     "field_descriptors": ()
   }
 
@@ -556,6 +587,7 @@ following declaration within their type stubs or source files:
       eq_default: bool = True,
       order_default: bool = False,
       kw_only_default: bool = False,
+      transform_descriptor_types: bool = False,
       field_descriptors: tuple[type | Callable[..., Any], ...] = (),
   ) -> Callable[[_T], _T]:
       # If used within a stub file, the following implementation can
@@ -676,6 +708,18 @@ users of Django would need to explicitly declare the ``id`` field.
 This limitation may make it impractical to use the
 ``dataclass_transform`` mechanism with Django.
 
+Class-wide default values
+-------------------------
+
+SQLAlchemy requested that we expose a way to specify that the default
+value of all fields in the transformed class is None. It is typical
+that all of their fields are optional and None indicates that the
+field is not set.
+
+We chose not to support this feature, since it is specific to
+SQLAlchemy. Users can manually set ``default=None`` on these fields
+instead.
+
 Open Issues
 ===========