rest parameters don't work in async arrow functions unless args array is accessed without spreading (T7260)

[babel-bot]

Issue originally made by @spudly

Options

preset-es2015, preset-stage-3

Input code

const callTest = async (...args) => {
    await test(...args);
  };

  const test = (arg) => console.log(arg);

  callTest('yo');

Description

This is similar to: T2776: Generators and async functions with default args place _this and _arguments incorrectly.

When you use an async arrow function that uses a rest arg and then spread the resulting array into another function call without first accessing the variable, the _arguments variable is placed outside of the function, causing it to send the wrong arguments.

Simply accessing the variable fixes this issue. All I have to do is add "args;" as the first line in the callTest() function and it starts working.

Tested with the REPL at babeljs.io, version 6.7.4.

[babel-bot]

Comment originally made by @loganfsmyth

Yup, looks like this is https://phabricator.babeljs.io/T1882 re-introduced in 6.7.0 from my changes to shadow processing. I'll need to dig in a bit to figure out a good solution.

[babel-bot]

Comment originally made by @loganfsmyth

Reintroduced by 42d3844

[olalonde]

Is this still an issue? Wasn't able to reproduce.

[danharper]

Seems to still be an issue.

e.g. When using preset-latest, args references arguments from outside the function:

const callTest = async (...args) => {
  await test(...args);
};

"use strict";

var _arguments = arguments; // <-------

function _asyncToGenerator(fn) { return function () { var gen = fn.apply(this, arguments); return new Promise(function (resolve, reject) { function step(key, arg) { try { var info = gen[key](arg); var value = info.value; } catch (error) { reject(error); return; } if (info.done) { resolve(value); } else { return Promise.resolve(value).then(function (value) { step("next", value); }, function (err) { step("throw", err); }); } } return step("next"); }); }; }

var callTest = function () {
    var _ref = _asyncToGenerator(regeneratorRuntime.mark(function _callee() {
        var _args = _arguments; // <-------
        return regeneratorRuntime.wrap(function _callee$(_context) {
            while (1) {
                switch (_context.prev = _context.next) {
                    case 0:
                        _context.next = 2;
                        return test.apply(undefined, _args); // <-------

                    case 2:
                    case "end":
                        return _context.stop();
                }
            }
        }, _callee, undefined);
    }));

    return function callTest(_x) {
        return _ref.apply(this, arguments);
    };
}();

[olalonde]

I'm not sure if it's the presets I'm using but:

$ cat test-async.js
const callTest = async (...args) => {
  await test(...args);
};

const test = (arg) => console.log(arg);

callTest('hello')

$ babel-node test-async.js
hello

Compiled code:

'use strict';

function _asyncToGenerator(fn) { return function () { var gen = fn.apply(this, arguments); return new Promise(function (resolve, reject) { function step(key, arg) { try { var info = gen[key](arg); var value = info.value; } catch (error) { reject(error); return; } if (info.done) { resolve(value); } else { return Promise.resolve(value).then(function (value) { step("next", value); }, function (err) { step("throw", err); }); } } return step("next"); }); }; }

const callTest = (() => {
  var _ref = _asyncToGenerator(function* () {
    yield test(...arguments);
  });

  return function callTest() {
    return _ref.apply(this, arguments);
  };
})();

const test = arg => console.log(arg);

callTest('hello');

Ah, I think I'm not actually compiling array rest/spread because it's supported by Node v6.

[spudly]

Definitely still an issue, at least with the version in use on the website.

Try it out

Notice that when you comment out line 2 in the original code, the compiled code starts to fail because it now uses a new _arguments variable which is defined outside of the function (line 3).

[gpittarelli]

I've reproduced this using presets stage-0 and es2015 on current master, and noticed that it doesn't occur if you do one run with only stage-0 and then another run with es2015.

I further dug into the individual plugins, and while I'm still digging, I believe it only happens when transform-async-to-generator and transform-es2015-parameters are in the same pass.

[danez]

This has been fixed in the 7.0 branch and will be backported to 6.0 with #5567.

[existentialism]

Release in v6.24.1!