Meta Decorator

[deckar01]

Add an experimental decorator for declaring meta attributes that inherits by default.

Resolves #1879

[sloria]

the @overload usage seems a bit odd...does the approach with TypedDict and total=False not work? like what we do here?

marshmallow/src/marshmallow/fields.py

Lines 87 to 98 in f0c6afb

	class _BaseFieldKwargs(typing.TypedDict, total=False):
	load_default: typing.Any
	dump_default: typing.Any
	data_key: str | None
	attribute: str | None
	validate: types.Validator | typing.Iterable[types.Validator] | None
	required: bool
	allow_none: bool | None
	load_only: bool
	dump_only: bool
	error_messages: dict[str, str] | None
	metadata: typing.Mapping[str, typing.Any] | None

or perhaps

def meta(
    *bases: SchemaMeta,
    fields: tuple[str, ...] | list[str] | None,
    additional: tuple[str, ...] | list[str] | None,
    # ...
    **kwargs,
):
    def wrapper(schema):
        mro = bases if bases else (schema.Meta,)
        meta = type(schema.Meta.__name__, mro, {
            "fields": fields,
            "additional": additional,
             # ...
             **kwargs
        })
        return type(schema.__name__, (schema,), {"Meta": meta})

    return wrapper

[deckar01]

Unpack[TypedDict] does not allow accepting extra kwargs, but we allow custom Meta attributes.

Explicitly copying the args into a dictionary defines missing attributes as None, which breaks inheritance.

One @overloadis all that is needed (and is valid), but mypy requires a sacrificial overload.

[sloria]

Ah I see. In that case, maybe just add comments about why this approach is necessary. Could even include a link to that gh comment

[sloria]

Should this be

Suggested change

	*bases: SchemaMeta,
	*bases: Schema.Meta,

? Surprised mypy doesn't raise an error in the tests tho 🤔