Fix: array-bracket-newline consistent error with comments (fixes #12416)

[mdjermanovic]

What is the purpose of this pull request? (put an "X" next to item)

[X] Bug fix #12416

Tell us about your environment

• ESLint Version: 6.5.1
• Node Version: 10.16.0
• npm Version: 6.9.0

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

default

Please show your full configuration:

Configuration

module.exports = {
  parserOptions: {
    ecmaVersion: 2015,
  }
};

What did you do? Please include the actual source code causing the issue.

Online Demo Link

/*eslint array-bracket-newline: ["error", "consistent"]*/

const foo = [ // comment
  1,
  2
];

What did you expect to happen?

No errors.

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

  3:13  error  There should be no linebreak after '['   array-bracket-newline
  6:1   error  There should be no linebreak before ']'  array-bracket-newline

What changes did you make? (Give an overview)

Check for the linebreak between [ and the first non-comment token inside, instead of between [ and the first token including comments.

Is there anything you'd like reviewers to focus on?

This was certainly unexpected behavior of the consistent option, given that always option doesn't report errors on the same code (Demo Link).

All tests added in valid were invalid before this change.

Two added invalid tests were already invalid, but in a different way. The rule was reporting unexpected linebreaks after the opening brackets (Demo Link). After the change, the rule will report missing linebreaks before the closing brackets.

I think that this change in general cannot generate more warnings - arrays/patterns that were valid will stay valid. The only difference, apart from fixing the original example, is in what the rule reports in cases such as those two invalid.

[g-plane]

LGTM, thanks!