Comma dangle syntax no longer ignores functions: never

[willlma]

Tell us about your environment

• ESLint Version:
  Upgraded from 6.51 to 6.8.0
• Node Version:
  v13.12.0
• npm Version:
  Using yarn: 1.22.4

What parser (default, Babel-ESLint, etc.) are you using?
Babel-ESLint
Please show your full configuration:

Configuration

extends: airbnb
parser: babel-eslint
env:
  browser: true
rules:
  arrow-parens: [warn, always]
  comma-dangle: [warn, always-multiline, { "functions": never }]
  import/prefer-default-export: 0
  jsx-quotes: [warn, prefer-single]
  max-len: [warn, { code: 80 }]
  object-curly-newline: ["warn", { "multiline": true, "consistent": true }]
  operator-linebreak: [warn, after]
  radix: [warn, as-needed]
  react/destructuring-assignment: [warn, always, { ignoreClassFields: true }]
  react/jsx-filename-extension: 0
  react/jsx-props-no-spreading: 0
  react/state-in-constructor: 0
settings:
  import/resolver:
    webpack:
      config: './config/webpack/custom.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 store = createStore(
  combineReducers({ ...reducers }),
  initialState,
  applyMiddleware(thunk)
);

yarn lint

What did you expect to happen?
No warnings. My .eslintrc specifies

comma-dangle: [warn, always-multiline, { "functions": never }]

which worked prior to this upgrade

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

warning  Missing trailing comma  comma-dangle

Are you willing to submit a pull request to fix this bug?
No

[mdjermanovic]

Hi @willlma, thanks for the bug report!

The actual bug, in this case, is that the rule doesn't report invalid configuration and just ignores the extra option { "functions": never }.

Your configuration works the same as:

comma-dangle: [warn, always-multiline]

Per the documentation, it should be either a string option or an object option. This particular rule doesn't support overriding the specified string option with an additional object option.

The correct configuration would be:

comma-dangle: [warn, {
    "arrays": "always-multiline",
    "objects": "always-multiline",
    "imports": "always-multiline",
    "exports": "always-multiline",
    "functions": "never" 
}]

In v6.5.1 [warn, always-multiline] actually used to ignore functions (it didn't disallow comma dangle), which was fixed in #12462.

[eslint-deprecated]

Unfortunately, it looks like there wasn't enough interest from the team
or community to implement this change. While we wish we'd be able to
accommodate everyone's requests, we do need to prioritize. We've found
that issues failing to reach accepted status after 21 days tend to
never be accepted, and as such, we close those issues.
This doesn't mean the idea isn't interesting or useful, just that it's
not something the team can commit to.

Thanks for contributing to ESLint and we appreciate your understanding.

[mdjermanovic]

Reopening because this looks like a bug in the rule's schema.

[kaicataldo]

@mdjermanovic Do you mind marking this as accepted if you've verified this bug and outlining what you believe the correct fix is here? That way someone from the community could pick this up!

[mdjermanovic]

Marked as accepted. PR #13166 to fix this is prepared, we're just not sure whether this can be a semver-minor fix or should we treat it as a breaking change.