Add type_hint to TransferTypeConverter.from_transfer_type

temporalio/converter/_payload_converter.py

@@ -81,9 +81,14 @@ def to_transfer_type(self, value: ValueT) -> TransferTypeT:
         raise NotImplementedError
 
     @abstractmethod
-    def from_transfer_type(self, value: TransferTypeT) -> ValueT:
+    def from_transfer_type(
+        self, value: TransferTypeT, type_hint: type[ValueT]
+    ) -> ValueT:
         """Convert a transfer type value to its user-facing value.
 
+        ``type_hint`` is the requested user-facing type, including concrete
+        generic arguments.
+
         .. warning::
             This API is experimental and subject to change.
         """
@@ -638,8 +643,10 @@ def from_payloads(
             payloads, typing.cast("list[type]", inner_type_hints)
         )
         return [
-            converter.from_transfer_type(value) if converter is not None else value
-            for value, converter in zip(values, converters)
+            converter.from_transfer_type(value, type_hint)
+            if converter is not None
+            else value
+            for value, converter, type_hint in zip(values, converters, type_hints)
         ]
 
     def with_context(self, context: SerializationContext) -> Self:

tests/test_converter.py

@@ -6,6 +6,7 @@
 import logging
 import sys
 import traceback
+import typing
 from collections import deque
 from collections.abc import Iterable, Mapping, MutableMapping, Sequence
 from dataclasses import dataclass
@@ -14,8 +15,11 @@
 from typing import (
     Any,
     Dict,  # type:ignore[reportDeprecated]
+    Generic,
     Literal,
     NewType,
+    TypeVar,
+    cast,
     get_args,
     get_type_hints,
 )
@@ -278,6 +282,7 @@ def to_transfer_type(
     def from_transfer_type(
         self,
         value: temporalio.api.common.v1.WorkflowExecution,
+        type_hint: type[TemporalTransferTypeValue],
     ) -> TemporalTransferTypeValue:
         return TemporalTransferTypeValue(value=value.workflow_id)
 
@@ -305,6 +310,7 @@ def to_transfer_type(
     def from_transfer_type(
         self,
         value: temporalio.api.common.v1.WorkflowExecution,
+        type_hint: type[TemporalTransferTypeValueWithoutHint],
     ) -> TemporalTransferTypeValueWithoutHint:
         return TemporalTransferTypeValueWithoutHint(value=value.workflow_id)
 
@@ -315,6 +321,47 @@ class TemporalTransferTypeValueWithoutHint:
     value: str
 
 
+T = TypeVar("T")
+
+
+@dataclass
+class TemporalTransferTypeGenericValue(Generic[T]):
+    value: T
+
+
+class TemporalTransferTypeGenericValueConverter(
+    TransferTypeConverter[
+        TemporalTransferTypeGenericValue[T],
+        temporalio.api.common.v1.WorkflowExecution,
+    ]
+):
+    transfer_type = temporalio.api.common.v1.WorkflowExecution
+
+    def to_transfer_type(
+        self, value: TemporalTransferTypeGenericValue[T]
+    ) -> temporalio.api.common.v1.WorkflowExecution:
+        return temporalio.api.common.v1.WorkflowExecution(
+            workflow_id=str(value.value),
+            run_id="run-id",
+        )
+
+    def from_transfer_type(
+        self,
+        value: temporalio.api.common.v1.WorkflowExecution,
+        type_hint: type[TemporalTransferTypeGenericValue[T]],
+    ) -> TemporalTransferTypeGenericValue[T]:
+        converted_value: str | int = value.workflow_id
+        if typing.get_args(type_hint)[0] is int:
+            converted_value = int(converted_value)
+        return TemporalTransferTypeGenericValue(value=cast(T, converted_value))
+
+
+# Register after both classes are defined so the generic type can be resolved.
+transfer_type_convertible(TemporalTransferTypeGenericValueConverter)(
+    TemporalTransferTypeGenericValue
+)
+
+
 class CustomDefaultPayloadConverter(DefaultPayloadConverter):
     pass
 
@@ -358,6 +405,30 @@ def test_temporal_transfer_type_payload_converter_without_transfer_type_hint():
     )
 
 
+@pytest.mark.parametrize(
+    ("value", "type_hint"),
+    [
+        (
+            TemporalTransferTypeGenericValue("workflow-id"),
+            TemporalTransferTypeGenericValue[str],
+        ),
+        (
+            TemporalTransferTypeGenericValue(123),
+            TemporalTransferTypeGenericValue[int],
+        ),
+    ],
+)
+def test_temporal_transfer_type_payload_converter_with_generic_value(
+    value: TemporalTransferTypeGenericValue[T],
+    type_hint: type[TemporalTransferTypeGenericValue[T]],
+):
+    converter = DataConverter.default.payload_converter
+
+    payload = converter.to_payload(value)
+
+    assert converter.from_payload(payload, type_hint) == value
+
+
 def test_transfer_type_convertible_rejects_existing_converter():
     with pytest.raises(TypeError, match="already has a transfer type converter"):
         transfer_type_convertible(TemporalTransferTypeValueConverter)(