type Pizza = { type: 'pizza'; topping: string };
type Sandwich = { type: 'sandwich'; condiments: string[] };
type Food = Pizza | Sandwich;

const food = { type: 'pizza', topping: 'cheese' } as Food;

// These patterns used to be reject, but now work:

if (isMatching({ topping: 'cheese' }, food)) {
    // food: Food & { topping: 'cheese' }
}

if (isMatching({ unknownProp: P.instanceOf(Error) }, food)) {
// food: Food & { unknownProp: Error }
}