Schema for an "Open Union" of string literals

[carcigenicate]

Hello,

I have a field that can be one of multiple strings, or any string. I want to set it up like this so I can provide Typescript-level suggestions for the most common values, but also allow anything. In Typescript, that can be achieved by adding (string & {}) to the union as mentioned here:

type UnionWithSuggestions = 'a' | 'b' | 'c' | 'd' | (string & {});

I tried implementing the same using schemas, and the Typescript portion works as expected, but it causes a schema validation failure:

import {Type, Static} from '@sinclair/typebox';
import {TypeCompiler} from '@sinclair/typebox/compiler';

const UnionSchema = Type.Union([
  Type.Intersect([Type.String(), Type.Object({})]),
  Type.Literal('a'),
  Type.Literal('b'),
  Type.Literal('c'),
  Type.Literal('d'),
]);

type UnionSchemaType = Static<typeof UnionSchema>;

const union: UnionSchemaType = 'something else';  // No TS error, as expected

// But

const compiled = TypeCompiler.Compile(UnionSchema);
const validated = compiled.Check('something else');
console.log(validated);  // false - Validation failed

Is it possible to achieve something similar that will allow for string suggestions while allowing all strings, and pass both TS and schema validation?

Thank you

[sinclairzx81]

@carcigenicate Hi,

Is it possible to achieve something similar that will allow for string suggestions while allowing all strings, and pass both TS and schema validation?

Probably the easiest way to achieve this is to use the Unsafe type to override type inference.

Docs: https://sinclairzx81.github.io/typebox/#/docs/type/unsafe

Ref: Example

import Type, { type Static } from 'typebox'

// this type will validate for all strings, but infer with the ... | (string & {})
const T = Type.Unsafe<'a' | 'b' | 'c' | 'd' | (string & {})>(Type.String())

type T = Static<typeof T>

This type will validate for all strings, but will auto complete for the known variants (and allow additional via (string & {}).

Hope this helps
S

[carcigenicate]

Thank you, that does indeed do exactly what I want. I've been shying away from Unsafe because of its name, but apparently I need to learn it.