Disallow extra nonexistent fields (#290)

* Do not allow extra nonexistent fields

* Add test case

* Raise a RuntimeError instead of AssertionError

---------

Co-authored-by: Fabrice Normandin <fabrice.normandin@gmail.com>

simple_parsing/wrappers/dataclass_wrapper.py

@@ -295,17 +295,23 @@ def set_default(self, value: DataclassT | dict | None):
         self._default = value
         if field_default_values is None:
             return
+        unknown_names = set(field_default_values)
         for field_wrapper in self.fields:
             if field_wrapper.name not in field_default_values:
                 continue
             # Manually set the default value for this argument.
             field_default_value = field_default_values[field_wrapper.name]
             field_wrapper.set_default(field_default_value)
+            unknown_names.remove(field_wrapper.name)
         for nested_dataclass_wrapper in self._children:
             if nested_dataclass_wrapper.name not in field_default_values:
                 continue
             field_default_value = field_default_values[nested_dataclass_wrapper.name]
             nested_dataclass_wrapper.set_default(field_default_value)
+            unknown_names.remove(nested_dataclass_wrapper.name)
+        unknown_names.discard("_type_")
+        if unknown_names:
+            raise RuntimeError(f"{sorted(unknown_names)} are not fields of {self.dataclass} at path {self.dest!r}!")
 
     @property
     def title(self) -> str:

test/test_set_defaults.py

@@ -40,6 +40,26 @@ def test_set_defaults_from_file(tmp_path: Path):
     assert args.foo == saved_config
 
 
+def test_set_broken_defaults_from_file(tmp_path: Path):
+    parser = ArgumentParser()
+    parser.add_arguments(Foo, dest="foo")
+
+    saved_config = Foo(a=456, b="HOLA")
+    config_path = tmp_path / "broken_foo.yaml"
+    broken_yaml = to_dict(saved_config)
+    broken_yaml["i_do_not_exist"] = 3
+    with open(config_path, "w") as f:
+        yaml.dump({"foo": broken_yaml}, f)
+
+    with pytest.raises(
+        RuntimeError,
+        match=(
+            r"\['i_do_not_exist'\] are not fields of <class 'test.test_set_defaults.Foo'> at path 'foo'!"
+        ),
+    ):
+        parser.set_defaults(config_path)
+
+
 def test_set_defaults_from_file_without_root(tmp_path: Path):
     """test that set_defaults accepts the fields of the dataclass directly, when the parser has
     nested_mode=NestedMode.WITHOUT_ROOT.