prefer-arrow-callback fix conflicting with prettier fix

[ismail-syed]

Edit by @lydell: TL;DR We recommend turning off these rules for the time being:

{
  "rules": {
    "arrow-body-style": "off",
    "prefer-arrow-callback": "off"
  }
}

---

What version of eslint are you using?
v4.9.0

What version of prettier are you using?
v1.7.4

What version of eslint-plugin-prettier are you using?
v2.3.1

Please paste any applicable config files that you're using (e.g. .prettierrc or .eslintrc files)
https://github.com/ismail-syed/prettier-eslint-config-invalid-code

What source code are you linting?

function foo() {
  return isTrue && [0,1,2].map(function(num) {
    return num * 2;
  });
}

What did you expect to happen?
The code above should be formatted as per prettiers config and also should adhere to that prefer-arrow-callback fix

What actually happened?
Invalid code was generated, closing parenthesis is missing on the return statement.

function foo() {
  return (
    isTrue &&
    [0, 1, 2].map((num) => {
    return num * 2;
  });
}

Is the underlying issue from the prefer-arrow-callback fixer or the prettier plugin fixer?

[lydell]

Is the underlying issue from the prefer-arrow-callback fixer or the prettier plugin fixer?

It could also be how ESLint applies fixes.

[not-an-aardvark]

Related: eslint/eslint#7928

tl;dr: Autofixes from rules can, on rare occasions, conflict with each other. Rules can work around the issue by coarsening their fixes to ensure that the "fix range" contains the entire range of text that caused the particular problem to be reported, rather than just the actual text replacement.

For convenience, could you paste the output of running ESLint without --fix when those two rules are enabled? I think this might be a problem with the core prefer-arrow-callback rule, but I'm not sure.

[ismail-syed]

Here is the output of running ESLint without --fix on issue2.js.

╰─$ yarn run lint
yarn run v1.1.0
$ eslint issue2.js --max-warnings 0

/Users/ismailsyed/test/prettier-eslint-config-invalid-code/issue2.js
  2:10  error  Replace `isTrue·&&·[0,1,` with `(⏎····isTrue·&&⏎····[0,·1,·`  prettier/prettier
  2:32  error  Unexpected function expression                                prefer-arrow-callback
  3:5   error  Insert `··`                                                   prettier/prettier  4:1   error  Replace `··}` with `····})⏎··`                                prettier/prettier

✖ 4 problems (4 errors, 0 warnings)
  4 errors, 0 warnings potentially fixable with the `--fix` option.

With --fix, I see parsing errors:

[not-an-aardvark]

Thanks for clarifying. This is actually a bug in eslint-plugin-prettier and is unrelated to the issue that I mentioned in #65 (comment). The problem is that eslint-plugin-prettier is providing separate "fixes" for each problem it reports, and the fixes are dependent on each other (in this case, one fix adds an opening paren, and another fix adds a closing paren). However, ESLint doesn't guarantee that it will be able to apply any given fix (e.g. if a fix overlaps with a fix from another rule).

It would probably be pretty difficult to determine which fixes need to be applied together as part of eslint-plugin-prettier. A simpler solution might be to just provide one "fix" which replaces the entire source text.

[victorporof]

Are there any plans to fix this?