require-atomic-updates false positive

[medikoo]

Tell us about your environment

• ESLint Version: 6.0.1
• Node Version: 12.4.0
• npm Version: 6.9.0

What parser (default, Babel-ESLint, etc.) are you using?

Default

Please show your full configuration:

https://github.com/medikoo/eslint-config-medikoo/blob/master/index.js

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

const fn = async someObj => {
  let { foo } = someObj;
  await Promise.resolve();
  // Possible race condition: `someObj.bar` might be reassigned based on an outdated value of `someObj.bar`
  someObj.bar = "whatever";
};

What did you expect to happen?

No error reported

What actually happened? Please include the actual, raw output from ESLint.

Error reported:

Possible race condition: `someObj.bar` might be reassigned based on an outdated value of 

Are you willing to submit a pull request to fix this bug?

Not at this point

[mysticatea]

Thank you for your report.

I think this is intentional behavior because that someObj object was read before await expression and written after await expression.

[medikoo]

I think this is intentional behavior because that someObj object was read before await expression and written after await expression.

Ok, but that's pretty aggressive assumption, as in many cases that can be an intentional well-thought construct

In place where it reported for me, it's totally intentional and there's no way to write it differently (aside of dropping async/await), due to that I needed to turn off this rule globally.

Still I'd love it to report for me cases as count += await getCount() which are error-prone obviously (and even if not, easy to write in a way they do not report)

[stinovlas]

I would say that if nothing else, error message is pretty misleading.

someObj.bar might be reassigned based on an outdated value of someObj.bar

That is simply not true, because someObj.bar = "whatever"; assigns string "whatever" which is not depending on someObj.bar in any way.

Also, it's not following the rule definition which clearly states that following must be true:

A variable or property is reassigned to a new value which is based on its old value.

[jwalton]

Here's a pretty vanilla Express middleware that triggers this problem, as you might see in any app that does virtual hosting based on the URL, if you're looking for a concrete example:

export function populateAccount() {
    return function(req, res, next) {
        Promise.resolve()
            .then(async () => {
                const host = req.headers['host'];
                req.account = await getAccount(host);
            })
            .then(() => next(), next);
    };
}
/*eslint require-atomic-updates: error */

Demo link.

[j0h]

@mysticatea could the following POC also be related to the issue?

function dataGetter() {
  return {};
}

function anotherDataGetter() {
  return {};
}

async function main() {
  let get_data = await dataGetter();

  const get_another_data = await anotherDataGetter(get_data.id);

  (() => {
    get_data[get_another_data.foo] = 1;
  });

  // Error Here: Possible race condition: `get_data` might be reassigned based on an outdated value of `get_data`.
  get_data = {
    ...get_data,
    ...get_another_data,
  };
}

main();

Demo Link