Fixed #22915 -- Document backward incompatible changes in the ValidationError constructor.

This patch also fixes update_error_dict to better handle the use case described
in this ticket, previously the type of the provided container could be lost in
some conditions.

Thanks Russell Keith-Magee for the report and Tim Graham for review.

1 files changed, 47 insertions, 0 deletions

diff --git a/tests/forms_tests/tests/test_forms.py b/tests/forms_tests/tests/test_forms.py
index 985ff8e2e0..23de5024fb 100644
--- a/tests/forms_tests/tests/test_forms.py
+++ b/tests/forms_tests/tests/test_forms.py
@@ -740,6 +740,53 @@ class FormsTestCase(TestCase):
         with six.assertRaisesRegex(self, ValueError, "has no field named"):
             f.add_error('missing_field', 'Some error.')
 
+    def test_update_error_dict(self):
+        class CodeForm(Form):
+            code = CharField(max_length=10)
+
+            def clean(self):
+                try:
+                    raise ValidationError({'code': [ValidationError('Code error 1.')]})
+                except ValidationError as e:
+                    self._errors = e.update_error_dict(self._errors)
+
+                try:
+                    raise ValidationError({'code': [ValidationError('Code error 2.')]})
+                except ValidationError as e:
+                    self._errors = e.update_error_dict(self._errors)
+
+                try:
+                    raise ValidationError({'code': forms.ErrorList(['Code error 3.'])})
+                except ValidationError as e:
+                    self._errors = e.update_error_dict(self._errors)
+
+                try:
+                    raise ValidationError('Non-field error 1.')
+                except ValidationError as e:
+                    self._errors = e.update_error_dict(self._errors)
+
+                try:
+                    raise ValidationError([ValidationError('Non-field error 2.')])
+                except ValidationError as e:
+                    self._errors = e.update_error_dict(self._errors)
+
+                # Ensure that the newly added list of errors is an instance of ErrorList.
+                for field, error_list in self._errors.items():
+                    if not isinstance(error_list, self.error_class):
+                        self._errors[field] = self.error_class(error_list)
+
+        form = CodeForm({'code': 'hello'})
+        # Trigger validation.
+        self.assertFalse(form.is_valid())
+
+        # Check that update_error_dict didn't lose track of the ErrorDict type.
+        self.assertTrue(isinstance(form._errors, forms.ErrorDict))
+
+        self.assertEqual(dict(form.errors), {
+            'code': ['Code error 1.', 'Code error 2.', 'Code error 3.'],
+            NON_FIELD_ERRORS: ['Non-field error 1.', 'Non-field error 2.'],
+        })
+
     def test_has_error(self):
         class UserRegistration(Form):
             username = CharField(max_length=10)