Minify: babel-generator: await (a||b) loses parentheses

[marcello3d]

const a = async () => await (a||b)

becomes

const a=async()=>await a||b;

should be

const a=async()=>await(a||b);

[ljharb]

Why should it be? await has very low precedence; although I like the parens for readability, I don't think they're required for the code to do the right thing.

[marcello3d]

It behaves different in Chrome (56.0.2924.87, macOS 64-bit), as far as I can tell:

const a = Promise.resolve(false)
const b = Promise.resolve('hi')
(async () => {
    console.log('await (a||b)', await (a||b))
    console.log('await a||b', await a||b)
})()

outputs:

await (a||b) false
await a||b Promise {[[PromiseStatus]]: "resolved", [[PromiseValue]]: "hi"}

We found the bug because our electron app stopped behaving correctly after removing the babel async/await regenerator. The workaround we're using is to break it apart:

const temp = a || b
… await temp …

[ljharb]

Interesting - we should figure out what the spec says, just in case it's a chrome bug.

[marcello3d]

I'm not really sure how to read the ecmascript spec—it's pretty opaque to me. I can't even find the word "precedence," and "await" shows up almost everywhere.

One other data point: the babel regenerator seems to have the same behavior as Chrome.

I'll check out Firefox Developer once I'm on a faster connection.

[marcello3d]

Does this section mean anything to you? https://tc39.github.io/ecmascript-asyncawait/#UnaryExpression

[marcello3d]

Firefox Developer edition 53.0a2 (2017-03-06) (64-bit) has the same result:

await (a||b) false 
await a||b Promise { <state>: "fulfilled", <value>: "hi" }

[ljharb]

K, looks like it's confirmed as a bug :-)

[goto-bus-stop]

Seems like a babel-generator bug, it happens even without any plugins:

➜  /tmp cat .babelrc
cat: .babelrc: No such file or directory

➜  /tmp cat test.js
const a = async () => await (a||b)

➜  /tmp babel test.js
const a = async () => await a || b;

[hzoo]

@babel-bot move to babel/babel

[hzoo]

Hey @marcello3d! I've moved your issue to the correct repository. Please make sure to keep an eye on the new issue for the latest information.

[hzoo]

^ this is so cool 😍

[hzoo]

Fixed https://github.com/babel/babel/issues/5428 via https://github.com/babel/babel/issues/5433, will be in next 7.0 release