fix: Serialize plan results to JSON compatible types earlier (#1464)

When a plan returns a value that is serializable but contains a nested
value that is not (eg a list of an unserializable type), the check for
whether it could be serialized was too lenient and the unserializable
type would be stored only to fail later when it was sent to the message
bus.

Converting the result to a json compatible type (using mode='json')
earlier allows any issues with nested fields to be caught and handled
appropriately.

Fixes #1447

Author: tpoliaw

src/blueapi/worker/event.py

@@ -4,6 +4,7 @@
 
 from bluesky.run_engine import RunEngineStateMachine
 from pydantic import Field, PydanticSchemaGenerationError, TypeAdapter
+from pydantic_core import PydanticSerializationError
 from super_state_machine.extras import PropertyMachine, ProxyString
 
 from blueapi.utils import BlueapiBaseModel
@@ -73,8 +74,8 @@ class TaskResult(BlueapiBaseModel):
     def from_result(cls, result: Any) -> Self:
         type_str = type(result).__name__
         try:
-            value = TypeAdapter(type(result)).dump_python(result)
-        except PydanticSchemaGenerationError:
+            value = TypeAdapter(type(result)).dump_python(result, mode="json")
+        except (PydanticSchemaGenerationError, PydanticSerializationError):
             value = None
         return cls(result=value, type=type_str)
 

tests/unit_tests/worker/test_task_worker.py

@@ -893,3 +893,22 @@ def test_plan_module_with_composite_devices_can_be_loaded_before_device_module(
     params = Task(name="injected_device_plan").prepare_params(context_without_devices)
     assert params["composite"].fake_device == fake_device
     assert params["composite"].second_fake_device == second_fake_device
+
+
+@pytest.mark.parametrize(
+    "plan_result,task_result,type_name",
+    (
+        (Unreturnable(foo=1, bar=[]), None, "Unreturnable"),
+        ((Unreturnable(foo=2, bar=[]),), None, "tuple"),
+        (ComplexReturn(foo=3, bar=["a"]), {"foo": 3, "bar": ["a"]}, "ComplexReturn"),
+        ((ComplexReturn(foo=4, bar=["b"]),), [{"foo": 4, "bar": ["b"]}], "tuple"),
+        (ModelReturn(foo=5, bar=["c"]), {"foo": 5, "bar": ["c"]}, "ModelReturn"),
+        ((ModelReturn(foo=6, bar=["d"]),), [{"foo": 6, "bar": ["d"]}], "tuple"),
+        (42, 42, "int"),
+        ((1, 2), [1, 2], "tuple"),
+    ),
+)
+def test_task_result_serialization(plan_result, task_result, type_name):
+    res = TaskResult.from_result(plan_result)
+    assert res.result == task_result
+    assert res.type == type_name