Tweak set customization

HISTORY.rst

@@ -13,6 +13,8 @@ History
 * PyPy support (and tests, using a minimal Hypothesis profile) restored.
   (`#253 <https://github.com/python-attrs/cattrs/issues/253>`_)
 * Fix propagating the `detailed_validation` flag to mapping and counter structuring generators.
+* Fix ``typing.Set`` applying too broadly when used with the ``GenConverter.unstruct_collection_overrides`` parameter on Python versions below 3.9. Switch to ``typing.AbstractSet`` on those versions to restore the old behavior.
+  (`#264 <https://github.com/python-attrs/cattrs/issues/264>`_)
 
 22.1.0 (2022-04-03)
 -------------------

docs/customizing.rst

@@ -5,7 +5,7 @@ Customizing class un/structuring
 This section deals with customizing the unstructuring and structuring processes in `cattrs`.
 
 Using ``cattr.Converter``
-********************************
+*************************
 
 The default ``Converter``, upon first encountering an ``attrs`` class, will use
 the generation functions mentioned here to generate the specialized hooks for it,
@@ -20,7 +20,7 @@ them for types using :py:attr:`Converter.register_structure_hook <cattrs.Convert
 flexible but also requires the most amount of boilerplate.
 
 Using ``cattrs.gen`` generators
-******************************
+*******************************
 
 `cattrs` includes a module, :mod:`cattrs.gen`, which allows for generating and
 compiling specialized functions for unstructuring ``attrs`` classes.

src/cattrs/_compat.py

@@ -1,8 +1,11 @@
 import builtins
 import sys
+from collections.abc import MutableSet as AbcMutableSet
+from collections.abc import Set as AbcSet
 from dataclasses import MISSING
 from dataclasses import fields as dataclass_fields
 from dataclasses import is_dataclass
+from typing import AbstractSet as TypingAbstractSet
 from typing import Any, Dict, FrozenSet, List
 from typing import Mapping as TypingMapping
 from typing import MutableMapping as TypingMutableMapping
@@ -109,9 +112,14 @@ def is_protocol(type: Any) -> bool:
     return issubclass(type, Protocol) and getattr(type, "_is_protocol", False)
 
 
+OriginAbstractSet = AbcSet
+OriginMutableSet = AbcMutableSet
+
 if is_py37 or is_py38:
     Set = TypingSet
+    AbstractSet = TypingAbstractSet
     MutableSet = TypingMutableSet
+
     Sequence = TypingSequence
     MutableSequence = TypingMutableSequence
     MutableMapping = TypingMutableMapping
@@ -241,6 +249,7 @@ def is_literal(_) -> bool:
             return False
 
     Set = AbcSet
+    AbstractSet = AbcSet
     MutableSet = AbcMutableSet
     Sequence = AbcSequence
     MutableSequence = AbcMutableSequence

src/cattrs/converters.py

@@ -16,9 +16,9 @@
     Mapping,
     MutableMapping,
     MutableSequence,
-    MutableSet,
+    OriginAbstractSet,
+    OriginMutableSet,
     Sequence,
-    Set,
     fields,
     get_newtype_base,
     get_origin,
@@ -647,23 +647,27 @@ def __init__(
         self.forbid_extra_keys = forbid_extra_keys
         self.type_overrides = dict(type_overrides)
 
+        unstruct_collection_overrides = {
+            get_origin(k) or k: v for k, v in unstruct_collection_overrides.items()
+        }
+
         self._unstruct_collection_overrides = unstruct_collection_overrides
 
         # Do a little post-processing magic to make things easier for users.
         co = unstruct_collection_overrides
 
         # abc.Set overrides, if defined, apply to abc.MutableSets and sets
-        if Set in co:
-            if MutableSet not in co:
-                co[MutableSet] = co[Set]
-                co[AbcMutableSet] = co[Set]  # For 3.7/3.8 compatibility.
+        if OriginAbstractSet in co:
+            if OriginMutableSet not in co:
+                co[OriginMutableSet] = co[OriginAbstractSet]
+                co[AbcMutableSet] = co[OriginAbstractSet]  # For 3.7/3.8 compatibility.
             if FrozenSetSubscriptable not in co:
-                co[FrozenSetSubscriptable] = co[Set]
+                co[FrozenSetSubscriptable] = co[OriginAbstractSet]
 
         # abc.MutableSet overrrides, if defined, apply to sets
-        if MutableSet in co:
+        if OriginMutableSet in co:
             if set not in co:
-                co[set] = co[MutableSet]
+                co[set] = co[OriginMutableSet]
 
         if FrozenSetSubscriptable in co:
             co[frozenset] = co[FrozenSetSubscriptable]  # For 3.7/3.8 compatibility.

src/cattrs/preconf/bson.py

@@ -5,7 +5,7 @@
 
 from bson import DEFAULT_CODEC_OPTIONS, CodecOptions, ObjectId, decode, encode
 
-from cattrs._compat import Set, is_mapping
+from cattrs._compat import AbstractSet, is_mapping
 from cattrs.gen import make_mapping_structure_fn
 
 from ..converters import BaseConverter, Converter
@@ -89,7 +89,7 @@ def gen_structure_mapping(cl: Any):
 def make_converter(*args, **kwargs) -> BsonConverter:
     kwargs["unstruct_collection_overrides"] = {
         **kwargs.get("unstruct_collection_overrides", {}),
-        Set: list,
+        AbstractSet: list,
     }
     res = BsonConverter(*args, **kwargs)
     configure_converter(res)

src/cattrs/preconf/json.py

@@ -4,7 +4,7 @@
 from json import dumps, loads
 from typing import Any, Type, TypeVar, Union
 
-from cattrs._compat import Counter, Set
+from cattrs._compat import AbstractSet, Counter
 
 from ..converters import BaseConverter, Converter
 
@@ -39,7 +39,7 @@ def configure_converter(converter: BaseConverter):
 def make_converter(*args, **kwargs) -> JsonConverter:
     kwargs["unstruct_collection_overrides"] = {
         **kwargs.get("unstruct_collection_overrides", {}),
-        Set: list,
+        AbstractSet: list,
         Counter: dict,
     }
     res = JsonConverter(*args, **kwargs)

src/cattrs/preconf/msgpack.py

@@ -4,7 +4,7 @@
 
 from msgpack import dumps, loads
 
-from cattrs._compat import Set
+from cattrs._compat import AbstractSet
 
 from ..converters import BaseConverter, Converter
 
@@ -35,7 +35,7 @@ def configure_converter(converter: BaseConverter):
 def make_converter(*args, **kwargs) -> MsgpackConverter:
     kwargs["unstruct_collection_overrides"] = {
         **kwargs.get("unstruct_collection_overrides", {}),
-        Set: list,
+        AbstractSet: list,
     }
     res = MsgpackConverter(*args, **kwargs)
     configure_converter(res)

src/cattrs/preconf/orjson.py

@@ -6,7 +6,7 @@
 
 from orjson import dumps, loads
 
-from cattrs._compat import Set, is_mapping
+from cattrs._compat import AbstractSet, is_mapping
 
 from ..converters import BaseConverter, Converter
 
@@ -69,7 +69,7 @@ def key_handler(v):
 def make_converter(*args, **kwargs) -> OrjsonConverter:
     kwargs["unstruct_collection_overrides"] = {
         **kwargs.get("unstruct_collection_overrides", {}),
-        Set: list,
+        AbstractSet: list,
     }
     res = OrjsonConverter(*args, **kwargs)
     configure_converter(res)

src/cattrs/preconf/tomlkit.py

@@ -5,7 +5,7 @@
 
 from tomlkit import dumps, loads
 
-from cattrs._compat import Set, is_mapping
+from cattrs._compat import AbstractSet, is_mapping
 
 from ..converters import BaseConverter, Converter
 from . import validate_datetime
@@ -59,7 +59,7 @@ def key_handler(k: bytes):
 def make_converter(*args, **kwargs) -> TomlkitConverter:
     kwargs["unstruct_collection_overrides"] = {
         **kwargs.get("unstruct_collection_overrides", {}),
-        Set: list,
+        AbstractSet: list,
         tuple: list,
     }
     res = TomlkitConverter(*args, **kwargs)

src/cattrs/preconf/ujson.py

@@ -5,7 +5,7 @@
 
 from ujson import dumps, loads
 
-from cattrs._compat import Set
+from cattrs._compat import AbstractSet
 
 from ..converters import BaseConverter, Converter
 
@@ -40,7 +40,7 @@ def configure_converter(converter: BaseConverter):
 def make_converter(*args, **kwargs) -> UjsonConverter:
     kwargs["unstruct_collection_overrides"] = {
         **kwargs.get("unstruct_collection_overrides", {}),
-        Set: list,
+        AbstractSet: list,
     }
     res = UjsonConverter(*args, **kwargs)
     configure_converter(res)

tests/test_unstructure_collections.py

@@ -59,6 +59,48 @@ def test_collection_unstructure_override_set():
     assert c.unstructure({1, 2, 3}) == [1, 2, 3]
 
 
+@pytest.mark.skipif(is_py39_plus, reason="Requires Python 3.8 or lower")
+def test_collection_unstructure_override_set_38():
+    """Test overriding unstructuring sets."""
+    from typing import AbstractSet, MutableSet, Set
+
+    # First approach, predicate hook with is_mutable_set
+    c = Converter()
+
+    c._unstructure_func.register_func_list(
+        [
+            (
+                is_mutable_set,
+                partial(c.gen_unstructure_iterable, unstructure_to=list),
+                True,
+            )
+        ]
+    )
+
+    assert c.unstructure({1, 2, 3}, unstructure_as=Set[int]) == [1, 2, 3]
+
+    # Second approach, using __builtins__.set
+    c = Converter(unstruct_collection_overrides={set: list})
+
+    assert c.unstructure({1, 2, 3}, unstructure_as=Set[int]) == [1, 2, 3]
+    assert c.unstructure({1, 2, 3}, unstructure_as=MutableSet[int]) == {1, 2, 3}
+    assert c.unstructure({1, 2, 3}) == [1, 2, 3]
+
+    # Second approach, using typing.MutableSet
+    c = Converter(unstruct_collection_overrides={MutableSet: list})
+
+    assert c.unstructure({1, 2, 3}, unstructure_as=Set[int]) == [1, 2, 3]
+    assert c.unstructure({1, 2, 3}, unstructure_as=MutableSet[int]) == [1, 2, 3]
+    assert c.unstructure({1, 2, 3}) == [1, 2, 3]
+
+    # Second approach, using typing.AbstractSet
+    c = Converter(unstruct_collection_overrides={AbstractSet: list})
+
+    assert c.unstructure({1, 2, 3}, unstructure_as=Set[int]) == [1, 2, 3]
+    assert c.unstructure({1, 2, 3}, unstructure_as=MutableSet[int]) == [1, 2, 3]
+    assert c.unstructure({1, 2, 3}) == [1, 2, 3]
+
+
 @pytest.mark.skipif(not is_py39_plus, reason="Requires Python 3.9+")
 def test_collection_unstructure_override_seq():
     """Test overriding unstructuring seq."""