const fn = /** @tupleReturn */ s => [s, s];

/** @tupleReturn */ interface Fn { (s: string): [string, string] }
const fn: Fn = s => [s, "bar"]; // the arrow function will now correctly keep return values unpacked

/** @tupleReturn */ declare function foo(): [string, string];
declare function bar(a: string, b: string): void;
bar(...foo()); // will no longer be 'bar(table.unpack({foo()}))'