Fix desert handling of metadata not being passed to fields

Author: isra17

src/desert/_make.py

@@ -220,8 +220,8 @@ def field_for_schema(
 
     if default is not marshmallow.missing:
         desert_metadata.setdefault("dump_default", default)
-        desert_metadata.setdefault("allow_none", True)
         desert_metadata.setdefault("load_default", default)
+        desert_metadata.setdefault("allow_none", True)
 
     field = None
 
@@ -235,9 +235,20 @@ def field_for_schema(
         field.metadata.update(metadata)
         return field
 
+    field_args = {
+        k: v
+        for k, v in desert_metadata.items()
+        if k
+        in [
+            "dump_default",
+            "load_default",
+            "allow_none",
+        ]
+    }
+
     # Base types
     if not field and typ in _native_to_marshmallow:
-        field = _native_to_marshmallow[typ](dump_default=default)
+        field = _native_to_marshmallow[typ](**field_args)
 
     # Generic types
     origin = typing_inspect.get_origin(typ)
@@ -253,16 +264,18 @@ def field_for_schema(
             collections.abc.Sequence,
             collections.abc.MutableSequence,
         ):
-            field = marshmallow.fields.List(field_for_schema(arguments[0]))
+            field = marshmallow.fields.List(
+                field_for_schema(arguments[0]), **field_args
+            )
 
         if origin in (tuple, t.Tuple) and Ellipsis not in arguments:
             field = marshmallow.fields.Tuple(  # type: ignore[no-untyped-call]
-                tuple(field_for_schema(arg) for arg in arguments)
+                tuple(field_for_schema(arg) for arg in arguments), **field_args
             )
         elif origin in (tuple, t.Tuple) and Ellipsis in arguments:
-
             field = VariadicTuple(
-                field_for_schema(only(arg for arg in arguments if arg != Ellipsis))
+                field_for_schema(only(arg for arg in arguments if arg != Ellipsis)),
+                **field_args,
             )
         elif origin in (
             dict,
@@ -275,47 +288,40 @@ def field_for_schema(
             field = marshmallow.fields.Dict(
                 keys=field_for_schema(arguments[0]),
                 values=field_for_schema(arguments[1]),
+                **field_args,
             )
         elif typing_inspect.is_optional_type(typ):
             [subtyp] = (t for t in arguments if t is not NoneType)
             # Treat optional types as types with a None default
-            metadata[_DESERT_SENTINEL]["dump_default"] = metadata.get(
-                "dump_default", None
-            )
-            metadata[_DESERT_SENTINEL]["load_default"] = metadata.get(
-                "load_default", None
-            )
-            metadata[_DESERT_SENTINEL]["required"] = False
-
-            field = field_for_schema(subtyp, metadata=metadata, default=None)
-            field.dump_default = None
-            field.load_default = None
-            field.allow_none = True
+            metadata[_DESERT_SENTINEL]["allow_none"] = True
+            if default is marshmallow.missing:
+                default = None
+            field = field_for_schema(subtyp, metadata=metadata, default=default)
 
         elif typing_inspect.is_union_type(typ):
             subfields = [field_for_schema(subtyp) for subtyp in arguments]
             import marshmallow_union
 
-            field = marshmallow_union.Union(subfields)
+            field = marshmallow_union.Union(subfields, **field_args)
 
     # t.NewType returns a function with a __supertype__ attribute
     newtype_supertype = getattr(typ, "__supertype__", None)
     if newtype_supertype and typing_inspect.is_new_type(typ):
         metadata.setdefault("description", typ.__name__)
-        field = field_for_schema(newtype_supertype, default=default)
+        field = field_for_schema(newtype_supertype, metadata=metadata, default=default)
 
     # enumerations
     if type(typ) is enum.EnumMeta:
         import marshmallow_enum
 
-        field = marshmallow_enum.EnumField(typ, metadata=metadata)
+        field = marshmallow_enum.EnumField(typ, metadata=metadata, **field_args)
 
     # Nested dataclasses
     forward_reference = getattr(typ, "__forward_arg__", None)
 
     if field is None:
         nested = forward_reference or class_schema(typ)
-        field = marshmallow.fields.Nested(nested)
+        field = marshmallow.fields.Nested(nested, **field_args)
 
     field.metadata.update(metadata)
 
@@ -350,11 +356,11 @@ def _get_field_default(
     if isinstance(field, dataclasses.Field):
         # misc: https://github.com/python/mypy/issues/10750
         # comparison-overlap: https://github.com/python/typeshed/pull/5900
-        if field.default_factory != dataclasses.MISSING:
-            return dataclasses.MISSING
-        if field.default is dataclasses.MISSING:
-            return marshmallow.missing
-        return field.default
+        if field.default_factory is not dataclasses.MISSING:
+            return field.default_factory
+        if field.default is not dataclasses.MISSING:
+            return field.default
+        return marshmallow.missing
     elif isinstance(field, attr.Attribute):
         if field.default == attr.NOTHING:
             return marshmallow.missing

tests/test_make.py

@@ -224,6 +224,17 @@ class A:
     assert data == A(None)  # type: ignore[call-arg]
 
 
+def test_optional_default(module: DataclassModule) -> None:
+    """Setting an optional type allows passing None."""
+
+    @module.dataclass
+    class A:
+        x: t.Optional[int] = 1
+
+    data = desert.schema_class(A)().load({})
+    assert data == A(1)  # type: ignore[call-arg]
+
+
 def test_custom_field(module: DataclassModule) -> None:
     @module.dataclass
     class A: