Turn off prefer-arrow-callback by default

[ismail-syed]

👋 Would it be appropriate to add prefer-arrow-callback to the list of conflicting rules to be turned off?

I had issues with this rule conflicting with our eslint config (which extends this prettier config). Turning off prefer-arrow-callback solved our issues.

Can I submit a PR?

[lydell]

I use prefer-arrow-callback together with Prettier every day without issues. What problem are you facing? Are you sure that there's no other tool or rule that causes your trouble?

[ismail-syed]

Thanks for the fast reply! Still investigating a bit more, but I believe you're right. I'll keep digging and report back if anything comes up.

[ismail-syed]

@lydell I have a reproducible issue here: https://github.com/ismail-syed/prettier-eslint-config-invalid-code

Could this be the result of perfer-arrow-callback's fix and prettier conflicting with eachother in the specific cases listed in issue1.js and issue2.js?

[lydell]

Thanks!

I managed to reduce the test cases.

.eslintrc.js:

module.exports = {
  env: {es6: true},
  plugins: ["prettier"],
  rules: {
    "prettier/prettier": "error",
    "prefer-arrow-callback": "error",
  }
}

issue1.js:

(
  f(function() {
    return
  })
) ||
1;

issue2.js:

function f() {
  return 1 && g(function() {
    return
  });
}

A strange thing is that if I comment out "prettier/prettier": "error", and run either of these commands:

eslint foo.js --fix && prettier --write foo.js
prettier --write foo.js && eslint foo.js --fix

... the error does not happen. Neither does it if I:

1. Comment out one of the rules.
2. eslint --fix foo.js
3. Uncomment the rule, comment out the other rule.
4. eslint --fix foo.js

So it seems to only happen when having both rules enabled and fixed at the same time.

You have found a bug somewhere! The solution is not to add prefer-arrow-callback to eslint-config-prettier, but to fix the bug.

@not-an-aardvark Do you have any idea what could be going on?

[ismail-syed]

Yay!

I went ahead and created an issue in eslint-plugin-prettier: prettier/eslint-plugin-prettier#65 as well.

I think the underlying bug exists in eslint-plugin-prettier's fix or prefer-arrow-callback's fix, it would be more appropriate to have issue(s) logged there.

[lydell]

prefer-arrow-callback (and arrow-body-style) are now disabled by default in v4.0.0. See the docs for more information.