@phpstan-type Pizza   array{type: 'pizza', toppings: Topping[]}
@phpstan-type Pasta   array{type: 'pasta', salsa: Salsa}
@phpstan-type Meal    Pizza|Pasta

/**
 * @param Meal $meal
 */
function ($meal) {
    if ($meal['type'] === 'pizza') {
        \PHPStan\dumpType($meal); // array{type: 'pizza', toppings: Topping[]} (Pizza)
    } else {
        \PHPStan\dumpType($meal); // array{type: 'pasta', salsa: Salsa} (Pasta)
    }
}