Custom data type validation does not support custom error generation

[weshouman]

Brief

Generating a custom error requires the field to be known, however defining a custom datatype only captures the value, and not the field.

Current Behaviour

The following works

    def _validate_type_ymd_date(self, value):
        """ Define custom validator for date format YYYY-MM-DD """
        try:
            datetime.strptime(value, '%Y-%m-%d')
            return True
        except ValueError:
            # self._error(field, f"Date '{value}' is not in YYYY-MM-DD format")
            return False

But adding a field argument to propagate an error is not supported

    def _validate_type_ymd_date(self, field, value):
        """ Define custom validator for date format YYYY-MM-DD """
        try:
            datetime.strptime(value, '%Y-%m-%d')
            return True
        except ValueError:
            self._error(field, f"Date '{value}' is not in YYYY-MM-DD format")
            return False

Showing the error

Traceback (most recent call last):
  File "/path/to/project/tests/test_validator.py", line 29, in test_ymd_date_valid
    self.assertTrue(self.validator.validate(document))
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/project/venv/lib/python3.11/site-packages/cerberus/validator.py", line 1040, in validate
    self.__validate_definitions(definitions, field)
  File "/path/to/project/venv/lib/python3.11/site-packages/cerberus/validator.py", line 1110, in __validate_definitions
    result = validate_rule(rule)
             ^^^^^^^^^^^^^^^^^^^
  File "/path/to/project/venv/lib/python3.11/site-packages/cerberus/validator.py", line 1085, in validate_rule
    return validator(definitions.get(rule, None), field, value)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/path/to/project/venv/lib/python3.11/site-packages/cerberus/validator.py", line 1548, in _validate_type
    matched = type_handler(value)
              ^^^^^^^^^^^^^^^^^^^
TypeError: MyValidator._validate_type_ymd_date() missing 1 required positional argument: 'value'

Expected Behaviour

Support the field argument for the type validators, for example

    def _validate_type_ymd_date(self, field, value):

beside

    def _validate_type_ymd_date(self, value):

Test Case

class TestYMDDate(unittest.TestCase):
    def setUp(self):
        self.validator = MyValidator({'start_date': {'type': 'ymd_date'}})

    def test_ymd_date_valid(self):
        document = {'start_date': '2023-01-01'}
        self.assertTrue(self.validator.validate(document))

Passes for 2 arg based validator but not for 3 arg based

Workaround

Stick to checking the default error generated when a type is not matched, in this case it would be must be of ymd_date type