Add support for validating against uuid values that are structs which implement the Stringer interface.

[JoshGlazebrook]

Fixes Or Enhances

This adds the ability to validate UUIDs that have an underlying struct value but also implement the Stringer interface. This should cover most UUID implementations (google's uuid, etc).

Implements: #900, specifically #900 (comment).

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• Tests exist or have been written that cover this particular change.

@go-playground/validator-maintainers

[coveralls]

coverage: 73.857% (+0.008%) from 73.849% when pulling fc09467 on JoshGlazebrook:uuid-stringer into 94a637a on go-playground:master.

[deankarn]

@JoshGlazebrook this PR is close :)

But I think it will fail for alias types that an implement fmt.Stringer. The type needs to be checked to see if the kind is already a string before attempting the cast. eg.

type uuidAlias string

func (u uuidAlias) String() string {
	return "This is a UUID " + string(u)
}

I think the new helper can be changed like so to avoid this and maintain 100% backward compatibility:

func fieldMatchesRegexByStringerValOrString(regex *regexp.Regexp, fl FieldLevel) bool {
	switch fl.Field().Kind() {
	case reflect.String:
		return regex.MatchString(fl.Field().String())
	default:
		if stringer, ok := fl.Field().Interface().(fmt.Stringer); ok {
			return regex.MatchString(stringer.String())
		} else {
			return regex.MatchString(fl.Field().String())
		}
	}
}

[deankarn]

I will merge and then make these changes.

[JoshGlazebrook]

Thank you!