Implement pickling for ValidationError (#1119)

src/errors/validation_exception.rs

@@ -341,6 +341,20 @@ impl ValidationError {
     fn __str__(&self, py: Python) -> String {
         self.__repr__(py)
     }
+
+    fn __reduce__(slf: &PyCell<Self>) -> PyResult<(&PyAny, PyObject)> {
+        let py = slf.py();
+        let callable = slf.getattr("from_exception_data")?;
+        let borrow = slf.try_borrow()?;
+        let args = (
+            borrow.title.as_ref(py),
+            borrow.errors(py, include_url_env(py), true, true)?,
+            borrow.input_type.into_py(py),
+            borrow.hide_input,
+        )
+            .into_py(slf.py());
+        Ok((callable, args))
+    }
 }
 
 // TODO: is_utf8_char_boundary, floor_char_boundary and ceil_char_boundary

tests/test_errors.py

@@ -1,4 +1,5 @@
 import enum
+import pickle
 import re
 import sys
 from decimal import Decimal
@@ -1074,3 +1075,17 @@ def test_hide_input_in_json() -> None:
 
     for error in exc_info.value.errors(include_input=False):
         assert 'input' not in error
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 9) and sys.implementation.name == 'pypy',
+    reason='PyPy before 3.9 cannot pickle this correctly',
+)
+def test_validation_error_pickle() -> None:
+    s = SchemaValidator({'type': 'int'})
+    with pytest.raises(ValidationError) as exc_info:
+        s.validate_python('definitely not an int')
+
+    original = exc_info.value
+    roundtripped = pickle.loads(pickle.dumps(original))
+    assert original.errors() == roundtripped.errors()