feat: add TopFieldError interface to expose parent struct reflection

[VDHewei]

feat: add TopFieldError interface exposing parent struct reflection

Description:
This PR introduces a new TopFieldError interface extending FieldError with:

• Top() reflect.Value method to access parent struct reflection
• Enables future tag inspection on ancestor structs
• Backward-compatible via interface assertion
• Lays foundation for advanced validation scenarios

Key Changes:

1. New interface in errors.go
2. Parent ref storage in fieldError
3. Validation context propagation
4. Tests for hierarchical field access

Use Case:

if topErr, ok := err.(validator.TopFieldError); ok {
    parentTags := topErr.Top().Type().Field(0).Tag // Access parent metadata
}

Rationale: Maintains validator flexibility while enabling deeper struct inspection capabilities.
(Let me know if you'd like to emphasize any specific technical aspect further.)

@go-playground/validator-maintainers

[VDHewei]

example:

MyStruct Struct {
  Data1 string `json:"data1" validate:"required" msg:"{jsonTag} must be required"`
}

func WarpValidatorError(err error) error {
	if err != nil {
		var (
			errMsg           []string
			validationErrors validator.ValidationErrors
		)
		if errors.As(err, &validationErrors) {
			for _, fieldErr := range validationErrors {
				if customMsg := getCustomTagMsg(fieldErr); customMsg != "" {
					errMsg = append(errMsg, customMsg)
				} else {
					errMsg = append(errMsg, fieldErr.Error())
				}
			}
		}
		if len(errMsg) > 0 {
			return fiber.NewError(fiber.StatusBadRequest, fmt.Sprintf("Parameter verification failed,%s", strings.Join(errMsg, ";")))
		}
		return err
	}
	return nil
}

func getCustomTagMsg(e error) string {
	var x validator.TopFieldError
	if !errors.As(e, &x) {
		return e.Error()
	} else {
		var (
			msg string
			t   = x.Top().Type()
		)
		// pointer type
		if t.Kind() == reflect.Ptr {
			t = t.Elem()
		}
		// slice type
		if t.Kind() == reflect.Slice || t.Kind() == reflect.Array {
			t = t.Elem()
		}
		name := x.Field()
		field, found := t.FieldByName(name)
		if !found {
			fmt.Printf("Field `%s` not found, param=%s,ns=%s\n", name, x.Param(), x.StructNamespace())
			return ""
		}
		if msg = field.Tag.Get("msg"); msg == "" {
			return msg
		}
		msg = strings.ReplaceAll(msg, "{fieldTag}", x.Field())
		msg = strings.ReplaceAll(msg, "{jsonTag}", splitAndGetFirst(field.Tag.Get("json"), ","))
		return msg
	}
}

func splitAndGetFirst(value, sep string) string {
	if value == "" {
		return ""
	}
	values := strings.Split(value, sep)
	if len(values) >= 1 {
		return values[0]
	}
	return ""
}