Fix BaseConverter.register_{un,}structure_hook type signature (#582)

Fix `BaseConverter.register_{un,}structure_hook` type signature

Author: Tinche

HISTORY.md

@@ -9,6 +9,11 @@ The third number is for emergencies when we need to start branches for older rel
 
 Our backwards-compatibility policy can be found [here](https://github.com/python-attrs/cattrs/blob/main/.github/SECURITY.md).
 
+## 24.1.2 (UNRELEASED)
+
+- Fix {meth}`BaseConverter.register_structure_hook` and {meth}`BaseConverter.register_unstructure_hook` type hints.
+  ([#581](https://github.com/python-attrs/cattrs/issues/581) [#582](https://github.com/python-attrs/cattrs/pull/582))
+
 ## 24.1.1 (2024-09-11)
 
 - Fix {meth}`BaseConverter.register_structure_hook_factory` and {meth}`BaseConverter.register_unstructure_hook_factory` type hints.

src/cattrs/converters.py

@@ -133,6 +133,9 @@
     bound="HookFactory[StructureHook] | ExtendedStructureHookFactory[Converter]",
 )
 
+UnstructureHookT = TypeVar("UnstructureHookT", bound=UnstructureHook)
+StructureHookT = TypeVar("StructureHookT", bound=StructureHook)
+
 
 class UnstructureStrategy(Enum):
     """`attrs` classes unstructuring strategies."""
@@ -308,7 +311,7 @@ def unstruct_strat(self) -> UnstructureStrategy:
         )
 
     @overload
-    def register_unstructure_hook(self) -> Callable[[UnstructureHook], None]: ...
+    def register_unstructure_hook(self, cls: UnstructureHookT) -> UnstructureHookT: ...
 
     @overload
     def register_unstructure_hook(self, cls: Any, func: UnstructureHook) -> None: ...
@@ -335,7 +338,7 @@ def register_unstructure_hook(
             cls = next(iter(sig.parameters.values())).annotation
             self.register_unstructure_hook(cls, func)
 
-            return None
+            return func
 
         if attrs_has(cls):
             resolve_types(cls)
@@ -440,10 +443,10 @@ def get_unstructure_hook(
         )
 
     @overload
-    def register_structure_hook(self) -> Callable[[StructureHook], None]: ...
+    def register_structure_hook(self, cl: StructureHookT) -> StructureHookT: ...
 
     @overload
-    def register_structure_hook(self, cl: Any, func: StructuredValue) -> None: ...
+    def register_structure_hook(self, cl: Any, func: StructureHook) -> None: ...
 
     def register_structure_hook(
         self, cl: Any, func: StructureHook | None = None
@@ -469,7 +472,7 @@ def register_structure_hook(
             func = cl
             sig = signature(func)
             self.register_structure_hook(sig.return_annotation, func)
-            return
+            return func
 
         if attrs_has(cl):
             resolve_types(cl)
@@ -481,6 +484,7 @@ def register_structure_hook(
             self._structure_func.register_func_list([(lambda t: t is cl, func)])
         else:
             self._structure_func.register_cls_list([(cl, func)])
+        return None
 
     def register_structure_hook_func(
         self, check_func: Predicate, func: StructureHook