Make validation notes pickable.

Certain test runners that pickle the exceptions raised to accumulate
them from multiple processes. For exceptions with `AttributeValidationNote`
and/or `IterableValidationNote`, because we have overriden __new__ on
these classes, pickle is not able to correctly unpickle them with the required
arguments. This implements __getnewargs__ to fix this problem.

Signed-off-by: Zixuan James Li <p359101898@gmail.com>

HISTORY.md

@@ -26,6 +26,8 @@
   ([#398](https://github.com/python-attrs/cattrs/issues/398) [#399](https://github.com/python-attrs/cattrs/pull/399))
 - Broaden loads' type definition for the preconf orjson converter.
   ([#400](https://github.com/python-attrs/cattrs/pull/400))
+- `AttributeValidationNote` and `IterableValidationNote` are now pickable.
+  ([#408](https://github.com/python-attrs/cattrs/pull/408))
 
 ## 23.1.2 (2023-06-02)
 

src/cattrs/errors.py

@@ -40,6 +40,9 @@ def __new__(
         instance.type = type
         return instance
 
+    def __getnewargs__(self) -> Tuple[str, Union[int, str], Any]:
+        return (str(self), self.index, self.type)
+
 
 class IterableValidationError(BaseValidationError):
     """Raised when structuring an iterable."""
@@ -76,6 +79,9 @@ def __new__(cls, string: str, name: str, type: Any) -> "AttributeValidationNote"
         instance.type = type
         return instance
 
+    def __getnewargs__(self) -> Tuple[str, str, Any]:
+        return (str(self), self.name, self.type)
+
 
 class ClassValidationError(BaseValidationError):
     """Raised when validating a class if any attributes are invalid."""

tests/test_validation.py

@@ -2,13 +2,19 @@
 from typing import Dict, FrozenSet, List, Set, Tuple
 
 import pytest
+import pickle
 from attrs import define, field
 from attrs.validators import in_
 from hypothesis import given
 
 from cattrs import Converter
 from cattrs._compat import Counter
-from cattrs.errors import ClassValidationError, IterableValidationError
+from cattrs.errors import (
+    AttributeValidationNote,
+    ClassValidationError,
+    IterableValidationError,
+    IterableValidationNote,
+)
 
 
 def test_class_validation():
@@ -178,3 +184,20 @@ def test_hetero_tuple_validation():
     assert exc.value.exceptions[0].__notes__ == [
         "Structuring typing.Tuple[int, int, int] @ index 2"
     ]
+
+
+def test_notes_pickling():
+    """Validation notes should be picklable"""
+    note = pickle.loads(  # noqa: S301
+        pickle.dumps(IterableValidationNote("foo", "key", str))
+    )
+    assert note == "foo"
+    assert note.index == "key"
+    assert note.type is str
+
+    note = pickle.loads(  # noqa: S301
+        pickle.dumps(AttributeValidationNote("foo", "name", int))
+    )
+    assert note == "foo"
+    assert note.name == "name"
+    assert note.type is int