Restore frozensets when decoding typed JSON payloads

CHANGELOG.md

@@ -56,6 +56,9 @@ to include examples, links to docs, or any other relevant information.
 
 ### Fixed
 
+- Restore `frozenset` values when decoding JSON payloads with a `frozenset` type hint,
+  including nested frozen sets.
+
 - Ordinary absolute imports of already-loaded modules in sandboxed workflows no longer go through
   importlib's module locks, fixing intermittent `Failed validating workflow` errors on Python 3.10
   caused by a `KeyError` in `importlib._bootstrap._ModuleLock.acquire` when a garbage-collection

temporalio/converter/_payload_converter.py

@@ -1086,11 +1086,13 @@ def value_to_type(
                     ret_list.append(value_to_type(arg_type, item, custom_converters))
                 except Exception as err:
                     raise TypeError(f"Failed converting {hint} index {i}") from err
-        # If tuple, set, or deque convert back to that type
+        # If tuple, set, frozenset, or deque convert back to that type
         if origin is tuple:
             return tuple(ret_list)
         elif origin is set:
             return set(ret_list)
+        elif origin is frozenset:
+            return frozenset(ret_list)
         elif origin is collections.deque:
             return collections.deque(ret_list)
         return ret_list

tests/test_converter.py

@@ -351,6 +351,28 @@ class MyPydanticClass(pydantic.BaseModel):  # type: ignore[reportUnreachable]
         baz: UUID | None = None
 
 
+@pytest.mark.parametrize(
+    "hint",
+    [frozenset, frozenset[int], typing_extensions.FrozenSet[int]],  # type:ignore[reportDeprecated]
+)
+@pytest.mark.parametrize("value", [frozenset(), frozenset({1, 2})])
+def test_json_frozenset_round_trip(hint: Any, value: frozenset[int]):
+    converter = JSONPlainPayloadConverter()
+    payload = converter.to_payload(value)
+    assert payload is not None
+    converted = converter.from_payload(payload, hint)
+    assert isinstance(converted, frozenset)
+    assert converted == value
+
+
+def test_json_nested_frozenset_round_trip():
+    converter = JSONPlainPayloadConverter()
+    value = {frozenset({1, 2}), frozenset({3})}
+    payload = converter.to_payload(value)
+    assert payload is not None
+    assert converter.from_payload(payload, set[frozenset[int]]) == value
+
+
 def test_json_type_hints():
     converter = JSONPlainPayloadConverter()
 
@@ -439,6 +461,7 @@ def fail(hint: Any, value: Any) -> None:
     ok(deque[int], deque([5, 6]))
     ok(Sequence[int], [5, 6])
     fail(list[int], [1, 2, "3"])
+    fail(frozenset[int], [1, 2, "3"])
 
     # Dict-like
     ok(dict[str, MyDataClass], {"foo": MyDataClass("foo", 5, SerializableEnum.FOO)})