Use experimental TypeForm

This updates typing for events and PropertyKey to use TypeForm.
This is still experimental, but without it these interfaces either
don't work at all or don't work under some common cases.

Author: JordonPhillips

codegen/core/src/main/java/software/amazon/smithy/python/codegen/generators/SetupGenerator.java

@@ -183,6 +183,7 @@ private static void writePyproject(
                     reportUnusedVariable = false
                     reportUnnecessaryComparison = false
                     reportUnusedClass = false
+                    enableExperimentalFeatures = true
 
                     [tool.ruff]
                     target-version = "py312"

packages/smithy-core/pyproject.toml

@@ -9,6 +9,7 @@ dependencies = []
 [dependency-groups]
 dev = [
     "freezegun>=1.5.1",
+    "typing_extensions>=4.13.0"
 ]
 
 [build-system]

packages/smithy-core/src/smithy_core/aio/interfaces/__init__.py

@@ -11,6 +11,8 @@
 from .eventstream import EventPublisher, EventReceiver
 
 if TYPE_CHECKING:
+    from typing_extensions import TypeForm
+
     from ...deserializers import DeserializeableShape, ShapeDeserializer
     from ...schemas import APIOperation
     from ...serializers import SerializeableShape
@@ -162,7 +164,7 @@ def create_event_publisher[
         *,
         operation: "APIOperation[OperationInput, OperationOutput]",
         request: I,
-        event_type: type[Event],
+        event_type: "TypeForm[Event]",
         context: TypedProperties,
     ) -> EventPublisher[Event]:
         """Creates an event publisher for a protocol event stream.
@@ -184,7 +186,7 @@ def create_event_receiver[
         operation: "APIOperation[OperationInput, OperationOutput]",
         request: I,
         response: O,
-        event_type: type[Event],
+        event_type: "TypeForm[Event]",
         event_deserializer: Callable[["ShapeDeserializer"], Event],
         context: TypedProperties,
     ) -> EventReceiver[Event]:

packages/smithy-core/src/smithy_core/interfaces/__init__.py

@@ -2,13 +2,10 @@
 # SPDX-License-Identifier: Apache-2.0
 from asyncio import iscoroutinefunction
 from collections.abc import ItemsView, Iterator, KeysView, ValuesView
-from typing import (
-    Any,
-    Protocol,
-    TypeGuard,
-    overload,
-    runtime_checkable,
-)
+from typing import TYPE_CHECKING, Any, Protocol, TypeGuard, overload, runtime_checkable
+
+if TYPE_CHECKING:
+    from typing_extensions import TypeForm
 
 
 class URI(Protocol):
@@ -122,26 +119,18 @@ class PropertyKey[T](Protocol):
 
     For a concrete implementation, see :py:class:`smithy_core.types.PropertyKey`.
 
-    Note that unions and other special types cannot easily be used here due to being
-    incompatible with ``type[T]``. PEP747 proposes a fix to this case, but it has not
-    yet been accepted. In the meantime, there is a workaround. The PropertyKey must
-    be assigned to an explicitly typed variable, and the ``value_type`` parameter of
-    the constructor must have a ``# type: ignore`` comment, like so:
-
     .. code-block:: python
 
         UNION_PROPERTY: PropertyKey[str | int] = PropertyKey(
             key="union",
-            value_type=str | int,  # type: ignore
+            value_type=str | int,
         )
-
-    Type checkers will be able to use such a property as expected.
     """
 
     key: str
     """The string key used to access the value."""
 
-    value_type: type[T]
+    value_type: "TypeForm[T]"
     """The type of the associated value in the properties bag."""
 
     def __str__(self) -> str:

packages/smithy-core/src/smithy_core/types.py

@@ -9,7 +9,7 @@
 from datetime import datetime
 from email.utils import format_datetime, parsedate_to_datetime
 from enum import Enum
-from typing import Any, overload
+from typing import TYPE_CHECKING, Any, overload
 
 from .exceptions import ExpectationNotMetError
 from .interfaces import PropertyKey as _PropertyKey
@@ -22,6 +22,9 @@
     serialize_rfc3339,
 )
 
+if TYPE_CHECKING:
+    from typing_extensions import TypeForm
+
 _GREEDY_LABEL_RE = re.compile(r"\{(\w+)\+\}")
 
 type Document = (
@@ -163,29 +166,21 @@ def format(self, *args: object, **kwargs: str) -> str:
 class PropertyKey[T](_PropertyKey[T]):
     """A typed property key.
 
-    Note that unions and other special types cannot easily be used here due to being
-    incompatible with ``type[T]``. PEP747 proposes a fix to this case, but it has not
-    yet been accepted. In the meantime, there is a workaround. The PropertyKey must
-    be assigned to an explicitly typed variable, and the ``value_type`` parameter of
-    the constructor must have a ``# type: ignore`` comment, like so:
-
     .. code-block:: python
 
         UNION_PROPERTY: PropertyKey[str | int] = PropertyKey(
             key="union",
-            value_type=str | int,  # type: ignore
+            value_type=str | int,
         )
-
-    Type checkers will be able to use such a property as expected.
     """
 
     key: str
     """The string key used to access the value."""
 
-    value_type: type[T]
+    value_type: "TypeForm[T]"
     """The type of the associated value in the property bag."""
 
-    def __init__(self, *, key: str, value_type: type[T]) -> None:
+    def __init__(self, *, key: str, value_type: "TypeForm[T]") -> None:
         # Intern the key to speed up dict access
         object.__setattr__(self, "key", sys.intern(key))
         object.__setattr__(self, "value_type", value_type)

packages/smithy-core/tests/unit/test_types.py

@@ -3,7 +3,7 @@
 
 # pyright: reportPrivateUsage=false
 from datetime import UTC, datetime
-from typing import Any, assert_type, cast
+from typing import Any, assert_type
 
 import pytest
 from smithy_core.exceptions import ExpectationNotMetError
@@ -323,12 +323,9 @@ def test_properties_typed_pop() -> None:
 
 def test_union_property() -> None:
     properties = TypedProperties()
-    union = cast(
-        PropertyKey[str | int],
-        PropertyKey(
-            key="union",
-            value_type=str | int,  # type: ignore
-        ),
+    union = PropertyKey(
+        key="union",
+        value_type=str | int,
     )
 
     properties[union] = "foo"

pyproject.toml

@@ -34,6 +34,7 @@ aws_sdk_signers = {workspace = true }
 
 [tool.pyright]
 typeCheckingMode = "strict"
+enableExperimentalFeatures = true
 
 [tool.pytest.ini_options]
 asyncio_mode = "auto" # makes pytest run async tests without having to be marked with the @pytest.mark.asyncio decorator