Add support of the composed metadata into schema and field

src/kat_transform/__init__.py

@@ -6,9 +6,9 @@
 from .field import FieldSpec, I, O
 from .exceptions import FieldResolveError
 from .markers import ValueGetter, FieldValue
-from .metadata import SchemaMetadata, FieldMetadata
 from .resolve_fields import resolve_fields, resolve_getter
 from .util import get_item_type, is_typed_mapping, is_typed_sequence
+from .metadata import CombinedMetadata, SchemaMetadata, FieldMetadata
 
 __all__ = [
     "field",
@@ -31,7 +31,7 @@ def field(
     name: str,
     transform: typing.Callable[[I], O] | None = None,
     getter: str | collections.abc.Sequence[str] | typing.Callable[..., I | O] | None = None,
-    meta: FieldMetadata | None = None,
+    meta: FieldMetadata | CombinedMetadata[FieldMetadata] | None = None,
 ) -> FieldSpec[I, O]:
     """
     Shorthand for FieldSpec creation
@@ -40,7 +40,9 @@ def field(
 
 
 def schema(
-    name: str, *fields: FieldSpec[typing.Any, typing.Any], meta: SchemaMetadata | None = None
+    name: str,
+    *fields: FieldSpec[typing.Any, typing.Any],
+    meta: SchemaMetadata | CombinedMetadata[SchemaMetadata] | None = None,
 ) -> SchemaSpec:
     """
     Shorthand for SchemaSpec creation

src/kat_transform/field.py

@@ -1,12 +1,11 @@
 import typing
 import collections.abc
-from functools import cache
-from dataclasses import dataclass, field
+from dataclasses import dataclass
 
 
 from .util import get_by_name
 from .markers import ValueGetter
-from .metadata import FieldMetadata
+from .metadata import CombinedMetadata, FieldMetadata
 
 if typing.TYPE_CHECKING:
     from .schema import SchemaSpec
@@ -34,7 +33,7 @@ class FieldSpec(typing.Generic[I, O]):
     Define name, list of names or callable that will be used to get input value for this field
     """
 
-    metadata: FieldMetadata | None = None
+    metadata: FieldMetadata | CombinedMetadata[FieldMetadata] | None = None
     """
     Define metadata for this field
     """

src/kat_transform/metadata.py

@@ -1,11 +1,13 @@
 import typing
 
 T = typing.TypeVar("T", bound="Metadata")
+T_co = typing.TypeVar("T_co", bound="Metadata", covariant=True)
 
 
 class Metadata:
-    def __init__(self) -> None:
-        self.entries: tuple[Metadata, ...] = (self,)
+    @property
+    def entries(self: T_co) -> tuple[T_co, ...]:
+        return (self,)
 
     def get_metadata(self, metadata_type: type[T], exact: bool = False) -> T | None:
         for entry in self.entries:
@@ -17,14 +19,17 @@ def get_metadata(self, metadata_type: type[T], exact: bool = False) -> T | None:
 
         return None
 
-    def __or__(self, other: "Metadata") -> "CombinedMetadata":
-        return CombinedMetadata(*self.entries, *other.entries)
+    def __or__(self: T_co, other: T_co) -> "CombinedMetadata[T_co]":
+        return CombinedMetadata[T_co](*self.entries, *other.entries)
 
 
-class CombinedMetadata(Metadata):
-    def __init__(self, *entries: Metadata):
-        super().__init__()
-        self.entries: tuple[Metadata, ...] = entries
+class CombinedMetadata(Metadata, typing.Generic[T_co]):
+    def __init__(self, *entries: T_co):
+        self._entries: tuple[T_co, ...] = entries
+
+    @property
+    def entries(self) -> tuple[T_co, ...]:
+        return self._entries
 
 
 class FieldMetadata(Metadata):

src/kat_transform/schema.py

@@ -5,7 +5,7 @@
 
 from .field import FieldSpec
 from .markers import FieldValue
-from .metadata import SchemaMetadata
+from .metadata import CombinedMetadata, SchemaMetadata
 from .util import get_item_type, is_typed_mapping, is_typed_sequence
 
 
@@ -37,7 +37,7 @@ class SchemaSpec:
 
     name: str
     fields: collections.abc.Sequence[FieldSpec[typing.Any, typing.Any]]
-    metadata: SchemaMetadata | None = None
+    metadata: SchemaMetadata | CombinedMetadata[SchemaMetadata] | None = None
 
     def get(self, from_: typing.Any) -> frozenset[FieldValue]:
         """