Converters: copy() returns Self (#644)

Author: Tinche

HISTORY.md

@@ -28,6 +28,8 @@ Our backwards-compatibility policy can be found [here](https://github.com/python
   ([#519](https://github.com/python-attrs/cattrs/issues/519) [#588](https://github.com/python-attrs/cattrs/pull/588))
 - Generic PEP 695 type aliases are now supported.
   ([#611](https://github.com/python-attrs/cattrs/issues/611) [#618](https://github.com/python-attrs/cattrs/pull/618))
+- {meth}`Converter.copy` and {meth}`BaseConverter.copy` are correctly annotated as returning `Self`.
+  ([#644](https://github.com/python-attrs/cattrs/pull/644))
 - Many preconf converters (_bson_, stdlib JSON, _cbor2_, _msgpack_, _msgspec_, _orjson_, _ujson_) skip unstructuring `int` and `str` enums,
   leaving them to the underlying libraries to handle with greater efficiency.
   ([#598](https://github.com/python-attrs/cattrs/pull/598))

src/cattrs/converters.py

@@ -13,6 +13,7 @@
 
 from attrs import Attribute, resolve_types
 from attrs import has as attrs_has
+from typing_extensions import Self
 
 from ._compat import (
     ANIES,
@@ -981,7 +982,7 @@ def copy(
         unstruct_strat: UnstructureStrategy | None = None,
         prefer_attrib_converters: bool | None = None,
         detailed_validation: bool | None = None,
-    ) -> BaseConverter:
+    ) -> Self:
         """Create a copy of the converter, keeping all existing custom hooks.
 
         :param detailed_validation: Whether to use a slightly slower mode for detailed
@@ -1367,7 +1368,7 @@ def copy(
         unstruct_collection_overrides: Mapping[type, UnstructureHook] | None = None,
         prefer_attrib_converters: bool | None = None,
         detailed_validation: bool | None = None,
-    ) -> Converter:
+    ) -> Self:
         """Create a copy of the converter, keeping all existing custom hooks.
 
         :param detailed_validation: Whether to use a slightly slower mode for detailed