Support for mutually exclusive groups of validations chained with OR

[adam-shamaa]

• I have looked at the documentation here first?
• I have looked at the examples provided that may showcase my question here?

Package version eg. v9, v10:

v10

Issue, Question or Enhancement:

I'd like to defined groups of validations from existing rules and chain them together with an OR clause. Something along the lines of

var req struct {
	Email string `validate:"(bakedin_tag1,bakedin_tag2)|bakedin_tag3"`
}

The syntax above of using parentheses/brackets isn't supported so I've tried defining an alias for the (bakedin_tag_1, bakedin_tag_2) clause:

validate.RegisterAlias("lcase_email", "email,lowercase")

However, there's a bug where aliases can't be used with an OR operator (existing issue for this #766)

Seem like the only route would be avoiding an alias and defining a custom validator function which validates the email and lowercase rule. But I want to avoid this as I'd be re-creating the baked-in validation methods isEmail and isLowerCase

validator/baked_in.go

Lines 1675 to 1678 in a947377

	// isEmail is the validation function for validating if the current field's value is a valid email address.
	func isEmail(fl FieldLevel) bool {
	return emailRegex().MatchString(fl.Field().String())
	}

validator/baked_in.go

Lines 2707 to 2719 in a947377

	// isLowercase is the validation function for validating if the current field's value is a lowercase string.
	func isLowercase(fl FieldLevel) bool {
	field := fl.Field()
	if field.Kind() == reflect.String {
	if field.String() == "" {
	return false
	}
	return field.String() == strings.ToLower(field.String())
	}
	panic(fmt.Sprintf("Bad field type %T", field.Interface()))
	}

As these methods are private to the validator package so I can't reference them.

Code sample, to showcase or reproduce:

package main

import (
	"github.com/go-playground/validator/v10"
)

type Example struct {
	Email string `validate:"lcase_email|empty_string"`
}

func main() {
	validate := validator.New()
	validate.RegisterAlias("lcase_email", "email,lowercase")
	validate.RegisterAlias("empty_string", "eq=")

	ex := &Example{
		Email: "badger.smith@gmail.com",
	}

	err := validate.Struct(ex)
	if err != nil {
		println(err.Error())
	}
}