Support x-nullable as an alternative to nullable behind an option

[mitchell-merry]

What is the problem this feature would solve?

In Swagger 2.0, there is no way to represent that a type is "nullable", i.e., that null is a valid value to pass to it (like nullable in Openapi 3.0.x).

External documents/projects?

No mention of nullable in the 2.0 spec: https://swagger.io/specification/v2/

nullable: true is how it is done in 3.0.x: https://swagger.io/docs/specification/data-models/data-types#null

(3.1.x uses an anyOf with null)

What is the feature you are proposing to solve the problem?

A common convention is to use x-nullable to represent this instead. I would like it if kubb supported this (specifically, for swagger-zod).

I recently implemented this in openapi-typescript: openapi-ts/openapi-typescript#1576, and need this feature to maintain feature parity (currently we cannot use these zod schemas as they miss this crucial feature). If approved, I would make the PR to support it here.

The core of the change would effectively be changing this:

const nullable = schema.nullable ?? false

to this (but exposed as an option):

const nullable = (schema.nullable || schema["x-nullable"]) ?? false

What alternatives have you considered?

Upgrading to 3.1.x... but that is impossible for a number of reasons right now 😅

[mitchell-merry]

I think to solve this, we would need to resolve this issue (kogosoftwarellc/open-api#768) in openapi-types first, though

Edit: I raised a PR; kogosoftwarellc/open-api#899, but also I think we need to bump the package in oas as well. That is, if it gets merged ever, I don't know how actively maintained it is 😄

To be clear, I think this needs this PR since otherwise it thinks that the schemas can't have x-* fields, so we can't check x-nullable without a ts-ignore comment.

[stijnvanhulle]

@mitchell-merry It would of course be nice if this could be fixed in oas but I will open a PR that will add the logic you suggested const nullable = (schema.nullable || schema["x-nullable"]) ?? false so the issue here will be resolved :)

[stijnvanhulle]

Fixed with version 2.7.2