Error when using anyOf with null and object type

[florianreinhart]

I ran into this issue when trying to create a JSON schema for fastify. We have a property that can either be null or be an object. I've created a simple example to reproduce the issue:

const fastJson = require("fast-json-stringify")

const mySchema = {
    type: "object",
    properties: {
        myProperty: {
            anyOf: [
                {
                    type: "object",
                    properties: {
                        propertyA: {
                            type: "string"
                        }
                    }
                },
                {
                    type: "null",
                }
            ]
        }
    }
}

const stringify = fastJson(mySchema)

let json = stringify({
    myProperty: null
})
console.log(json)

json = stringify({
    myProperty: {
        propertyA: "hello"
    }
})
console.log(json)

It looks like fast-json-stringify generates invalid code:

ReferenceError: $mainmyPropertyundefined is not defined
    at $main (eval at build (/test/fast-json-stringify/node_modules/fast-json-stringify/index.js:99:20), <anonymous>:77:9)
    at Object.<anonymous> (/test/fast-json-stringify/index.js:31:8)
    at Module._compile (module.js:643:30)
    at Object.Module._extensions..js (module.js:654:10)
    at Module.load (module.js:556:32)
    at tryModuleLoad (module.js:499:12)
    at Function.Module._load (module.js:491:3)
    at Function.Module.runMain (module.js:684:10)
    at startup (bootstrap_node.js:187:16)
    at bootstrap_node.js:608:3

[mcollina]

Nice one! Would you like to send a PR?

[florianreinhart]

I can dig into it. But I don't know much about JSON schema or fast-json-stringify, yet. Can you point me where to start looking in the fast-json-stringify code?

[mcollina]

I would probably start writing a unit test and search for the anyOf keyword.