Add an experimental meta decorator

Author: deckar01

src/marshmallow/experimental/meta.py

@@ -0,0 +1,69 @@
+from __future__ import annotations
+
+import typing
+
+from marshmallow.fields import Field
+from marshmallow.schema import SchemaMeta
+from marshmallow.types import UnknownOption
+
+
+@typing.overload
+def meta(
+    *bases: SchemaMeta,
+    fields: tuple[str, ...] | list[str] | None,
+    additional: tuple[str, ...] | list[str] | None,
+    include: dict[str, Field] | None,
+    exclude: tuple[str, ...] | list[str] | None,
+    many: bool | None,
+    dateformat: str | None,
+    datetimeformat: str | None,
+    timeformat: str | None,
+    render_module: typing.Any | None,
+    index_errors: bool | None,
+    load_only: tuple[str, ...] | list[str] | None,
+    dump_only: tuple[str, ...] | list[str] | None,
+    unknown: UnknownOption | None,
+    register: bool | None,
+    **kwargs,
+):
+    """
+    :param *bases: The meta classes to inherit from. Inherits from the decorated schema's
+        Meta class by default. Pass `None` to prevent inheritance.
+    :param fields: Fields to include in the (de)serialized result
+    :param additional: Fields to include in addition to the explicitly declared fields.
+        `additional <marshmallow.Schema.Meta.additional>` and `fields <marshmallow.Schema.Meta.fields>`
+        are mutually-exclusive options.
+    :param include: Dictionary of additional fields to include in the schema. It is
+        usually better to define fields as class variables, but you may need to
+        use this option, e.g., if your fields are Python keywords.
+    :param exclude: Fields to exclude in the serialized result.
+        Nested fields can be represented with dot delimiters.
+    :param many: Whether data should be (de)serialized as a collection by default.
+    :param dateformat: Default format for `Date <marshmallow.fields.Date>` fields.
+    :param datetimeformat: Default format for `DateTime <marshmallow.fields.DateTime>` fields.
+    :param timeformat: Default format for `Time <marshmallow.fields.Time>` fields.
+    :param render_module:  Module to use for `loads <marshmallow.Schema.loads>` and `dumps <marshmallow.Schema.dumps>`.
+        Defaults to `json` from the standard library.
+    :param index_errors: If `True`, errors dictionaries will include the index of invalid items in a collection.
+    :param load_only: Fields to exclude from serialized results
+    :param dump_only: Fields to exclude from serialized results
+    :param unknown: Whether to exclude, include, or raise an error for unknown fields in the data.
+        Use `EXCLUDE`, `INCLUDE` or `RAISE`.
+    :param register: Whether to register the `Schema <marshmallow.Schema>` with marshmallow's internal
+        class registry. Must be `True` if you intend to refer to this `Schema <marshmallow.Schema>`
+        by class name in `Nested` fields. Only set this to `False` when memory
+        usage is critical. Defaults to `True`.
+    """
+
+
+@typing.overload
+def meta(*bases, **kwargs): ...
+
+
+def meta(*bases, **kwargs):
+    def wrapper(schema):
+        mro = bases if bases else (schema.Meta,)
+        meta = type(schema.Meta.__name__, mro, kwargs)
+        return type(schema.__name__, (schema,), {"Meta": meta})
+
+    return wrapper

tests/test_meta.py

@@ -0,0 +1,37 @@
+from marshmallow import Schema
+from marshmallow.experimental.meta import meta
+
+
+class Base(Schema):
+    class Meta:
+        foo = True
+
+
+class TestMeta:
+    def test_default_inheritance(self):
+        @meta(bar=True)
+        class Test(Base):
+            pass
+
+        assert getattr(Test.Meta, "foo", None)
+        assert getattr(Test.Meta, "bar", None)
+
+    def test_explicit_inheritance(self):
+        class Parent(Schema):
+            class Meta:
+                bar = True
+
+        @meta(Base.Meta, Parent.Meta, baz=True)
+        class Test(Schema):
+            pass
+
+        assert getattr(Test.Meta, "foo", None)
+        assert getattr(Test.Meta, "bar", None)
+        assert getattr(Test.Meta, "baz", None)
+
+    def test_clear_inheritance(self):
+        @meta(Schema.Meta, bar=True)
+        class Test(Base):
+            pass
+
+        assert not hasattr(Test.Meta, "foo")