attrs structure hook factory: generate one-argument hooks (#597)

Author: Tinche

docs/migrations.md

@@ -19,3 +19,9 @@ The old behavior can be restored by explicitly passing in the old hook fallback
 # Or
 >>> c = BaseConverter(structure_fallback_factory=lambda _: raise_error)
 ```
+
+### `cattrs.gen.MappingStructureFn` and `cattrs.gen.DictStructureFn` removal
+
+The internal `cattrs.gen.MappingStructureFn` and `cattrs.gen.DictStructureFn` types were replaced by a more general type, `cattrs.SimpleStructureHook[In, T]`.
+If you were using `MappingStructureFn`, use `SimpleStructureHook[Mapping[Any, Any], T]` instead.
+If you were using `DictStructureFn`, use `SimpleStructureHook[Mapping[str, Any], T]` instead.

src/cattrs/converters.py

@@ -1,15 +1,15 @@
 from __future__ import annotations
 
 from collections import Counter, deque
-from collections.abc import Iterable
+from collections.abc import Callable, Iterable
 from collections.abc import Mapping as AbcMapping
 from collections.abc import MutableMapping as AbcMutableMapping
 from dataclasses import Field
 from enum import Enum
 from inspect import Signature
 from inspect import signature as inspect_signature
 from pathlib import Path
-from typing import Any, Callable, Optional, Tuple, TypeVar, overload
+from typing import Any, Optional, Tuple, TypeVar, overload
 
 from attrs import Attribute, resolve_types
 from attrs import has as attrs_has
@@ -82,7 +82,6 @@
 from .fns import Predicate, identity, raise_error
 from .gen import (
     AttributeOverride,
-    DictStructureFn,
     HeteroTupleUnstructureFn,
     IterableUnstructureFn,
     MappingUnstructureFn,
@@ -641,7 +640,9 @@ def _unstructure_union(self, obj: Any) -> Any:
 
     # Python primitives to classes.
 
-    def _gen_structure_generic(self, cl: type[T]) -> DictStructureFn[T]:
+    def _gen_structure_generic(
+        self, cl: type[T]
+    ) -> SimpleStructureHook[Mapping[str, Any], T]:
         """Create and return a hook for structuring generics."""
         return make_dict_structure_fn(
             cl, self, _cattrs_prefer_attrib_converters=self._prefer_attrib_converters

src/cattrs/gen/__init__.py

@@ -1,8 +1,8 @@
 from __future__ import annotations
 
 import re
-from collections.abc import Iterable, Mapping
-from typing import TYPE_CHECKING, Any, Callable, Final, Literal, TypeVar
+from collections.abc import Callable, Iterable, Mapping
+from typing import TYPE_CHECKING, Any, Final, Literal, TypeVar
 
 from attrs import NOTHING, Attribute, Factory
 from typing_extensions import NoDefault
@@ -69,7 +69,7 @@ def override(
 
 def make_dict_unstructure_fn_from_attrs(
     attrs: list[Attribute],
-    cl: type,
+    cl: type[T],
     converter: BaseConverter,
     typevar_map: dict[str, Any] = {},
     _cattrs_omit_if_default: bool = False,
@@ -282,12 +282,9 @@ def make_dict_unstructure_fn(
             del already_generating.working_set
 
 
-DictStructureFn = Callable[[Mapping[str, Any], Any], T]
-
-
 def make_dict_structure_fn_from_attrs(
     attrs: list[Attribute],
-    cl: type,
+    cl: type[T],
     converter: BaseConverter,
     typevar_map: dict[str, Any] = {},
     _cattrs_forbid_extra_keys: bool | Literal["from_converter"] = "from_converter",
@@ -299,7 +296,7 @@ def make_dict_structure_fn_from_attrs(
     _cattrs_use_alias: bool = False,
     _cattrs_include_init_false: bool = False,
     **kwargs: AttributeOverride,
-) -> DictStructureFn[T]:
+) -> SimpleStructureHook[Mapping[str, Any], T]:
     """
     Generate a specialized dict structuring function for a list of attributes.
 
@@ -663,7 +660,7 @@ def make_dict_structure_fn_from_attrs(
         globs[k] = v
 
     total_lines = [
-        f"def {fn_name}(o, _, {internal_arg_line}):",
+        f"def {fn_name}(o, _=__cl, {internal_arg_line}):",
         *lines,
         *post_lines,
         *instantiation_lines,
@@ -695,7 +692,7 @@ def make_dict_structure_fn(
     _cattrs_use_alias: bool = False,
     _cattrs_include_init_false: bool = False,
     **kwargs: AttributeOverride,
-) -> DictStructureFn[T]:
+) -> SimpleStructureHook[Mapping[str, Any], T]:
     """
     Generate a specialized dict structuring function for an attrs class or
     dataclass.