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Lua tuples and multi-return

Luau returns multiple values from a single function (return a, b, c). TypeScript represents this as a tuple [a, b, c].

Returns​

local function divmod(a, b)
  return a // b, a % b
end
function divmod(a, b) {
    return [a / b | 0, a % b];
}

Destructuring​

local q, r = divmod(10, 3)
const [q, r] = divmod(10, 3);

pcall and friends​

pcall returns [ok, ...values]:

local ok, result = pcall(risky, x)
const [ok, result] = pcall(risky, x);

Mixed-tuple-and-scalar issues​

When the right-hand side has multiple expressions, only the last expression's multi-return is unpacked. Everything before it contributes only its first value. This is a Luau rule and the compiler preserves it:

local a, b, c = 1, pcall(f)
-- a = 1
-- b = ok (boolean)
-- c = first return of f, or error message
const [, _ok, _r] = [1, ...pcall(f)] as [number, boolean, unknown];
const a = 1;
const [b, c] = [_ok, _r];

The compiler picks the simplest equivalent. For one-call-RHS, it uses plain destructuring with a multiret wrapper:

local a, b = pairs(t)
import { multiret } from 'luau2ts/runtime';

const [a, b] = multiret(pairs(t));

multiret is a no-op if the callee already returned a tuple, and lifts a scalar into [scalar] otherwise.