Drop support for using marshmallow_dataclas.dataclass directly

`marshmallow_dataclass.dataclass` is intended to be used only when using
`my_dataclass.Schema` to get the schema. But using this is not very
convenient when using type hints as they are not well supported by
`marshmallow`, as the `load()` function can't have hints.

This is actually why `load_config()` exists in the first place, so we
are using `class_schema()` instead, so we don't really need that our
types are decorated with `marshmallow_dataclass`, we can use the
built-in `dataclass` instead, we just need to add the appropriate
metadata if we want more complex validation.

Using `class_shema()` is also necessary to be able to pass a
`base_schema`, which we'll need when we want to use schemas with
custom fields, like the ones provided by `frequenz.quantities`.

Because of this, we just drop support for
`marshmallow_dataclass.dataclass` and we'll require that built-in
dataclasses are used in the future.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

RELEASE_NOTES.md

@@ -6,7 +6,7 @@
 
 ## Upgrading
 
-<!-- Here goes notes on how to upgrade from previous versions, including deprecations and what they should be replaced with -->
+- `frequenz.sdk.config.load_config()` doesn't accept classes decorated with `marshmallow_dataclass.dataclass` anymore. You should use the built-in `dataclasses.dataclass` directly instead, no other changes should be needed, the metadata in the `dataclass` fields will still be used.
 
 ## New Features
 

tests/config/test_util.py

@@ -7,7 +7,6 @@
 from typing import Any
 
 import marshmallow
-import marshmallow_dataclass
 import pytest
 from pytest_mock import MockerFixture
 
@@ -18,14 +17,6 @@
 class SimpleConfig:
     """A simple configuration class for testing."""
 
-    name: str
-    value: int
-
-
-@marshmallow_dataclass.dataclass
-class MmSimpleConfig:
-    """A simple configuration class for testing."""
-
     name: str = dataclasses.field(metadata={"validate": lambda s: s.startswith("test")})
     value: int
 
@@ -37,20 +28,9 @@ def test_load_config_dataclass() -> None:
     loaded_config = load_config(SimpleConfig, config)
     assert loaded_config == SimpleConfig(name="test", value=42)
 
-    config["name"] = "not test"
-    loaded_config = load_config(SimpleConfig, config)
-    assert loaded_config == SimpleConfig(name="not test", value=42)
-
-
-def test_load_config_marshmallow_dataclass() -> None:
-    """Test that load_config loads a configuration into a configuration class."""
-    config: dict[str, Any] = {"name": "test", "value": 42}
-    loaded_config = load_config(MmSimpleConfig, config)
-    assert loaded_config == MmSimpleConfig(name="test", value=42)
-
     config["name"] = "not test"
     with pytest.raises(marshmallow.ValidationError):
-        _ = load_config(MmSimpleConfig, config)
+        _ = load_config(SimpleConfig, config)
 
 
 def test_load_config_load_None() -> None:
@@ -70,7 +50,7 @@ def test_load_config_type_hints(mocker: MockerFixture) -> None:
     config: dict[str, Any] = {}
 
     # We add the type hint to test that the return type (hint) is correct
-    _: MmSimpleConfig = load_config(MmSimpleConfig, config, marshmallow_arg=1)
+    _: SimpleConfig = load_config(SimpleConfig, config, marshmallow_arg=1)
     mock_class_schema.return_value.load.assert_called_once_with(
         config, marshmallow_arg=1
     )