How to construct a new Type from an exiting Type's internal JSON representation?

[gabrielgrant]

Related to #1225 & #818

Type.toJSON()/.json return an internal representation of that type, parsed and reorganized from what is passed to `type():

const device = type({
	platform: "'android' | 'ios'",
	"versions?": "(number | string)[]"
})
const user = type({
	name: "string",
	device: device,
	"placeOfBirth?": "string"
})

user.toJSON()

gives

{
  required: [
    {
      key: 'device',
      value: {
        required: [ { key: 'platform', value: [ [Object], [Object] ] } ],
        optional: [
          {
            key: 'versions',
            value: { sequence: [Array], proto: 'Array' }
          }
        ],
        domain: 'object'
      }
    },
    { key: 'name', value: 'string' }
  ],
  optional: [ { key: 'placeOfBirth', value: 'string' } ],
  domain: 'object'
}

@ssalbdivad has previously mentioned that this output "can already round trip for the most part".

1. How should a a new Type be directly created from this internal representation?

   • passing user.json to type() doesn't work

   • passing user.json to rootSchema() from @ark/schema gives a type error (though does seem to work in this case if I ignore the TS error and run anyway?)

     Full error

     Argument of type 'Json' is not assignable to parameter of type 'Schema | { readonly meta?: MetaSchema; "meta.alias"?: string; "meta.optional"?: true; "meta.title"?: string; "meta.description"?: string; "meta.deprecated"?: true; "meta.default"?: unknown; ... 18 more ...; undeclared?: UndeclaredKeyBehavior; } | ... 4 more ... | Schema<...>'.
       Type 'JsonArray' is not assignable to type 'Schema | { readonly meta?: MetaSchema; "meta.alias"?: string; "meta.optional"?: true; "meta.title"?: string; "meta.description"?: string; "meta.deprecated"?: true; "meta.default"?: unknown; ... 18 more ...; undeclared?: UndeclaredKeyBehavior; } | ... 4 more ... | Schema<...>'.
         Type 'JsonData[]' is not assignable to type 'readonly (Schema | { readonly meta?: MetaSchema; "meta.alias"?: string; "meta.optional"?: true; "meta.title"?: string; "meta.description"?: string; "meta.deprecated"?: true; "meta.default"?: unknown; ... 18 more ...; undeclared?: UndeclaredKeyBehavior; } | ... 4 more ... | Schema<...>)[]'.
           Type 'JsonData' is not assignable to type 'Schema | { readonly meta?: MetaSchema; "meta.alias"?: string; "meta.optional"?: true; "meta.title"?: string; "meta.description"?: string; "meta.deprecated"?: true; "meta.default"?: unknown; ... 18 more ...; undeclared?: UndeclaredKeyBehavior; } | ... 4 more ... | Schema<...>'.
             Type 'null' is not assignable to type 'Schema | { readonly meta?: MetaSchema; "meta.alias"?: string; "meta.optional"?: true; "meta.title"?: string; "meta.description"?: string; "meta.deprecated"?: true; "meta.default"?: unknown; ... 18 more ...; undeclared?: UndeclaredKeyBehavior; } | ... 4 more ... | Schema<...>'.ts(2345)
     

const recreated = rootSchema(types.user.json)).
3. What are the limitations? (ie why is it "for the most part")

[ssalbdivad]

The limitations are non-serializable conditions. If your type includes .narrow functions, symbols, morphs etc. this won't work.

At some point, I'd like to have a more robust story around how hydration could work in cases like that (could coincide with the work needed for #810). Until then, it feels like there are too many caveats and it is too much to ask a user to understand which conditions are serializable to officially support this.

[gabrielgrant]

Hmmm...and does the typing issue I'm seeing come from those non-serializable conditions somehow being represented in the output JSON, but in a way that can't be re-hydrated? Or is that something else?

Thanks for the reply!

[ssalbdivad]

The typing issue is just because it's not officially supported until I have a good answer to the above issues.

That said, you can use it/wrap it to avoid a type error as long as you're aware of the limitations.