Creating XOR (exclusified) key types (solved, mostly) in typescript and typebox

[regis-underdog]

I have a need to create a schema where I have exclusive-or keys for a schema. For background, I have followed some interesting alleyways on the internet[1][2][3][4].

For clarity, I'll illustrate the solution as of Typebox 0.34.0 and Typescript 5.6.3 and Node 20:

function exclusiveKeySchema(key1: string, key2: string): TSchema {
  const xorSchema = Type.Union([
    Type.Object({ [key1]: Type.String(), [key2]: Type.Optional(Type.Never()) }),
    Type.Object({ [key2]: Type.String(), [key1]: Type.Optional(Type.Never()) }),
  ]);
  return Value.Clone(xorSchema);
}

such that

t1 = exclusiveKeySchema('foo', 'bar')

Value.Check(t1, {}) // false
Value.Check(t1, {foo: 'yes'}) // true
Value.Check(t1, {bar: 'yes'}) // true
Value.Check(t1, {foo: 'no', bar: 'no'}) // false YAY
Value.Check(t1, {foo: 'yes', something: 'no?'}) // true win some lose some, see [5]

Now expanding upward into my main objective:

const baseSchema = Type.Object({
  name: Type.String() // NO additionalProperties:false
});
const xorSchema = exclusiveKeySchema('foo', 'bar');
const fullSchema = Type.Intersect([baseSchema, xorSchema]); // NO additionalProperties: false

such that the results are nearly what we want (I have to reiterate that point [5] is still a potential issue)

t2 = fullSchema
// {
//  allOf: [
//    {
//      type: 'object',
//      properties: [Object],
//      required: [Array],
//      [Symbol(TypeBox.Kind)]: 'Object'
//    },
//    { anyOf: [Array], [Symbol(TypeBox.Kind)]: 'Union' }
//  ],
//  [Symbol(TypeBox.Kind)]: 'Intersect'
//}

Value.Check(t2, {}) //false
Value.Check(t2, {name: 'one'}) //false
Value.Check(t2, {name: 'one', foo: 'yes'}) // true
Value.Check(t2, {name: 'one', bar: 'yes'}) //true
Value.Check(t2, {name: 'one', foo: 'no', bar: 'no'}) // false YAY
Value.Check(t2, {name: 'one', foo: 'yes', extra: 'no?'}) // true can't win them all

[1] https://juhanajauhiainen.com/posts/how-to-type-an-object-with-exclusive-or-properties-in-typescript
[2] #60
[3] #151
[4] https://stackoverflow.com/a/44425486
[5] there are some compositions that work well so long as you keep unevaluatedProperties and additionalProperties as undefined. from [2]