Allow self references

[james-rabbit]

Describe the problem you are trying to fix (provide as much context as possible)

I use a success boolean key in message responses, and the structure of the message often depends on if it is true or false. I use Joi.alternatives to match on true or false but the syntax is pretty awkward and confusing for new readers (especially unknown()):

responseSchema: Joi.object({
	messageId: Joi.number(),
    success: Joi.boolean(),
).when(Joi.object({ success: true }).unknown(), {
	then: Joi.object({
		responseObject: Joi.object(),
		otherData: Joi.string(),
		isDataNew: Joi.boolean(),
	}),
	otherwise: Joi.object({
		reason: Joi.string().valid(Object.values(Constants.FailureReasons)),
		description: Joi.string().optional(),
	}),
}),

The line I think is strange is this one:

).when(Joi.object({ success: true }).unknown(), {

Which API (or modification of the current API) do you suggest to solve that problem ?

I would prefer a syntax that supported this case more easily and clearly.
I am not sure what the ideal solution would be, but maybe something like this would work:

responseSchema: Joi.object({
	messageId: Joi.number(),
    success: Joi.boolean().case({
        true: Joi.object({
		    responseObject: Joi.object(),
		    otherData: Joi.string(),
		    isDataNew: Joi.boolean(),
	    }),
        false: Joi.object({
		    reason: Joi.string().valid(Object.values(Constants.FailureReasons)),
		    description: Joi.string().optional(),
	    }),
    }),
),

Are you ready to work on a pull request if your suggestion is accepted ?

Honestly I am not sure I have the depth of understanding required to contribute to this project yet, I am just getting into it.

[Marsup]

This syntax would only work for strings though, and how do you define the default case ?

[james-rabbit]

I was only thinking of defining it for booleans really. The schema definition is powerful and I wouldn't want to define a whole parallel syntax to it.

I think the main thing that makes me feel like it's not already simple is the unknown(). If it was allowing unknown values for the when match by default then it could just be
).when({ success: true }, {
which is clear and has all the power of the schema.

Could this be solved by a validate-level option, something like allowUnknownInAlternatives?

[hueniverse]

responseSchema: Joi.object({
    messageId: Joi.number(),
    success: Joi.boolean(),
)
    .when('.success', {
        is: true,
        then: {
            responseObject: Joi.object(),
            otherData: Joi.string(),
            isDataNew: Joi.boolean()
        },
        otherwise: {
            reason: Joi.string().valid(Object.values(Constants.FailureReasons)),
            description: Joi.string().optional()
        }
    });

[james-rabbit]

I like the new self reference syntax, thank you @hueniverse!