SWC misunderstands precedence when using yield* expression

[danieltroger]

Describe the bug

Given this expression yield* (0, async_iterator) SWC will remove the parentheses and turn it into yield* 0, async_iterator, probably in an effort to remove bytes.

However, the precedence makes that actually say (yield* 0), async_iterator which is wrong and causing issues.

Input code

async function* level1(){
  yield 1;
  yield 2;
  yield 3;
}

async function* level2(){
  yield* (0, level1());
}

(async () => {
for await(const v of level2()){
  console.log(v);
}
})();

Config

Using parcel, I can share parcel config if needed. The issue is also reproducible on the REPL, please see attached link.

Playground link

https://play.swc.rs/?version=1.2.237&code=H4sIAAAAAAAAA23MwQrCMBCE4XueYo67RcTWY9B3CTGRwJIFGyOl9N2LEaIHb8PA%2F7l5yR7xmX1JmgdIqEFG4tUASwpyw2j7nL7zbM1mjPtXTz%2F1ADodOsotok9FjMsVq4n6gHu5VMhrngsqNHaoSe9fJRxF71SbsTGx3QGHOfQjuwAAAA%3D%3D&config=H4sIAAAAAAAAA02OsQ6DMAxEfwV5ZmgZOjB37UdYwUGpQoxsFxWh%2FHsTCmo3%2B3z3fBs81UG%2FwYyiJHXSNRm%2BoQdbZ1InYTZowbRIHqNSLotgUs8yVX%2BkEd16J8eCxgVh8qIWhlN4kOGAhn9xlJGsfCDtLt210COz0mFoYQop%2BLWyHU%2BzkOrvhGmMpzMX1sTDqwrbXndn3iD%2FGEcu6OMwfttRWvbM3qTgIaJac218EPL8bhYSDZwg5w%2Bx293IIgEAAA%3D%3D

Expected behavior

When exececuted, logs

1
2
3

to the console

Expected output code by SWC:

async function* level1() {
    yield 1;
    yield 2;
    yield 3;
}
async function* level2() {
    yield* (0, level1());
}
(async ()=>{
    for await (const v of level2()){
        console.log(v);
    }
})();

Actual behavior

When executed throws with: Uncaught (in promise) TypeError: 0 is not iterable

Actual output code by SWC:

async function* level1() {
    yield 1;
    yield 2;
    yield 3;
}
async function* level2() {
    yield* 0, level1();
}
(async ()=>{
    for await (const v of level2()){
        console.log(v);
    }
})();

Version

1.2.237

Additional context

This only happened by "doing a second pass" of SWC I guess?
So we built code to a library using parcel (parcel build with scope hoisting). Then we included that library in a project and built (parcel serve) it again and everything fell apart due to the aforementioned issue.

[danieltroger]

Thank you for the quick fix! @mischnic should I open a parcel issue to bump SWC version?

[mischnic]

@danieltroger parcel-bundler/parcel#8390

[swc-bot]

This closed issue has been automatically locked because it had no new activity for a month. If you are running into a similar issue, please create a new issue with the steps to reproduce. Thank you.