Support inject for default plan arguments again

When preparing the parameters for a plan, pydantic creates an instance
of the dynamically generated BaseModel, relying on the 'Reference' types
to convert from strings to instances of the devices. This includes
strings that are used as default field values (default parameters
created using the `inject` method).

We then convert the model back to a dictionary to pass as kwargs to the
plan. The previously used `model_fields_set` field on the model only
iterates over the fields set via the input JSON (the user supplied
arguments) and skips the fields populated via the default factories in
the base model. Using the `__pydantic_fields__` class variable, allows
all fields to be used including the defaults. This was previously
avoided as it generated warnings for unknown types but it is possible to
opt-out of these warnings.

src/blueapi/worker/task.py

@@ -22,7 +22,8 @@ class Task(BlueapiBaseModel):
 
     def prepare_params(self, ctx: BlueskyContext) -> Mapping[str, Any]:
         model = _lookup_params(ctx, self)
-        return _model_to_kwargs(model)
+        # Re-create dict manually to avoid nesting in model_dump output
+        return {field: getattr(model, field) for field in model.__pydantic_fields__}
 
     def do_task(self, ctx: BlueskyContext) -> None:
         LOGGER.info(f"Asked to run plan {self.name} with {self.params}")
@@ -49,22 +50,3 @@ def _lookup_params(ctx: BlueskyContext, task: Task) -> BaseModel:
     model = plan.model
     adapter = TypeAdapter(model)
     return adapter.validate_python(task.params)
-
-
-def _model_to_kwargs(model: BaseModel) -> Mapping[str, Any]:
-    """
-    Converts an instance of BaseModel back to a dictionary that
-    can be passed as **kwargs.
-    Used instead of BaseModel.model_dump() because we don't want
-    the dumping to be nested and because it fires UserWarnings
-    about data types it is unfamiliar with
-    (such as ophyd devices).
-
-    Args:
-        model: Pydantic model to convert to kwargs
-
-    Returns:
-        Mapping[str, Any]: Dictionary that can be passed as **kwargs
-    """
-
-    return {name: getattr(model, name) for name in model.model_fields_set}

tests/unit_tests/worker/test_task_worker.py

@@ -575,3 +575,26 @@ def test_begin_task_span_ok(
     task_id = worker.submit_task(_SIMPLE_TASK)
     with asserting_span_exporter(exporter, "begin_task", "task_id"):
         worker.begin_task(task_id)
+
+
+def test_injected_devices_are_found(
+    fake_device: FakeDevice,
+    context: BlueskyContext,
+):
+    def injected_device_plan(dev: FakeDevice = fake_device.name) -> MsgGenerator:  # type: ignore
+        yield from ()
+
+    context.register_plan(injected_device_plan)
+    params = Task(name="injected_device_plan").prepare_params(context)
+    assert params["dev"] == fake_device
+
+
+def test_missing_injected_devices_fail_early(
+    context: BlueskyContext,
+):
+    def missing_injection(dev: FakeDevice = "does_not_exist") -> MsgGenerator:  # type: ignore
+        yield from ()
+
+    context.register_plan(missing_injection)
+    with pytest.raises(ValueError):
+        Task(name="missing_injection").prepare_params(context)