don't show Undefined in default factory error

Author: davidhewitt

src/errors/validation_exception.rs

@@ -528,7 +528,8 @@ impl PyLineError {
         };
         write!(output, "  {message} [type={}", self.error_type.type_string())?;
 
-        if !hide_input {
+        // special case: don't show input for DefaultFactoryNotCalled errors - there is no valid input
+        if !hide_input && !matches!(self.error_type, ErrorType::DefaultFactoryNotCalled { .. }) {
             let input_value = self.input_value.bind(py);
             let input_str = safe_repr(input_value);
             write!(output, ", input_value=")?;

tests/validators/test_with_default.py

@@ -873,6 +873,6 @@ def __init__(self, a: int, b: int):
   Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='not_an_int', input_type=str]
     For further information visit https://errors.pydantic.dev/{pydantic_version}/v/int_parsing
 b
-  The default factory uses validated data, but at least one validation error occurred [type=default_factory_not_called, input_value=PydanticUndefined, input_type=PydanticUndefinedType]
+  The default factory uses validated data, but at least one validation error occurred [type=default_factory_not_called]
     For further information visit https://errors.pydantic.dev/{pydantic_version}/v/default_factory_not_called"""
     )