Incorrect comma-dangle error shown when using object rest/spread.

• ESLint Version: 4.3.0
• Node Version: 6.1.0.0
• npm Version: 3.10.10 What parser (default, Babel-ESLint, etc.) are you using? babel-eslint

Please show your full configuration:

Configuration

{
    "env": {
        "es6": true,
        "browser": true,
    },
    "extends": "airbnb",
    "plugins": [],
    "parser": "babel-eslint",
    "parserOptions": {
        "ecmaFeatures": {
            "experimentalDecorators": true
        }
    },
    "globals": {
        "SyntheticInputEvent": true,
        "SyntheticKeyboardEvent": true,
    },
    "rules": {
        "indent": ["error", 4, {
            "SwitchCase": 1
        }],
        "space-before-function-paren": ["error", "always"],
        "react/jsx-filename-extension": [1, {
            "extensions": [".js", ".jsx"]
        }],
        "react/jsx-indent": [2, 4],
        "react/jsx-indent-props": [2, 4],
        "import/no-unresolved": [2, {
            "ignore": ['^rdx', '^app', '^utils']
        }],
        "react/sort-comp": [0],
        "import/no-extraneous-dependencies": [0],
        "import/prefer-default-export": [0],
        "import/extensions": [0],
        "no-return-assign": [2, "except-parens"],
        "no-unneeded-ternary": ["error", {
            "defaultAssignment": true
        }],
        "valid-typeof": [0],
        "jsx-a11y/href-no-hash": "off",
        "jsx-a11y/label-has-for": "off",
        "class-methods-use-this": "off",
        "no-class-assign": "off",
        "linebreak-style": ["warn", "unix"]
    }
}

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 mapStateToProps = (
    state,
    {
        id,
        type,
        ...post, // <- ESLint says this comma shouldn't be here
    },
) => ({
    liked: true,
    ...post,
});

./node_modules/.bin/eslint path/to/file.js

What did you expect to happen? No errors.

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

6:16  error  Unexpected trailing comma  comma-dangle

1 problem (1, error, 0 warnings)
1 error, 0 warnings potentially fixable with the `--fix` option.

[not-an-aardvark]

Sure, but I don’t think it makes sense to use invalid JavaScript instead of valid JavaScript just for visual consistency. Presumably, you will need to run your code at some point, and JavaScript engines can only run valid JavaScript code.

I don’t think it would make sense to add an option that would encourage users to write invalid JavaScript. Of course, you could create a plugin that does this if you’d like, so that you could enforce it on an existing codebase (provided that you’re using a parser that also handles invalid trailing commas.)

[rbalicki2]

It’s a purely stylistic thing, and of course, I understand all the arguments to the contrary. It’s simply that the comma looks good and consistent, and seems logical. Visual consistently is important because when attempting to add lint rules to an existing code base and modify others’ behaviors, forcing developers to think causes them to resist the lint rules 😃

// e.g. the comma looks good here:
const MyComponent = ({
  className,
  ...props,
}) => { ... }