Unused vars not detected in destructuring assignment

[rajivshah3]

Tell us about your environment
macOS Mojave 10.14.2 Beta

• ESLint Version: v4.19.1, also reproducible on v5.11.1
• Node Version: v8.14.0
• npm Version: v6.4.1 (I normally use Yarn v1.12.3 though)

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

Please show your full configuration:

Configuration

env:
    browser: true
    es6: true
    commonjs: true
    node: true
    mocha: true
    jest: true
parser: babel-eslint
parserOptions:
    ecmaVersion: 6
    ecmaFeatures:
        experimentalObjectRestSpread: true
        jsx: true
        modules: true
        arrowFunctions: true
        classes: true
        spread: true

    sourceType: module
extends:
    - airbnb
    - eslint:recommended
    - plugin:react/recommended
    - prettier/react
    - prettier
plugins:
    - babel
    - react
    - jsx-a11y
settings:
    import/resolver:
        node:
            extensions:
                - .js
                - .json
                - .css
            paths:
                - ./src/desktop/src
                - ./src/shared
                - ./src/mobile/src

rules:
    arrow-parens: [2, "always"]
    block-scoped-var: 2
    brace-style: [2, 1tbs, { "allowSingleLine": true }]
    camelcase: 2
    curly: [2, "all"]
    dot-location: [1, "property"]
    dot-notation: 2
    eol-last: 2
    eqeqeq: 2
    key-spacing: 2
    keyword-spacing: 2
    linebreak-style: [0, "unix"]
    no-alert: 2
    no-console: 1
    no-else-return: 1
    no-empty: [2, { "allowEmptyCatch": true }]
    no-eq-null: 2
    no-eval: 2
    no-extend-native: 2
    no-floating-decimal: 2
    no-implicit-coercion: [2, { "allow": ["!!"] }]
    no-implied-eval: 2
    no-lone-blocks: 2
    no-loop-func: 2
    no-multi-spaces: 2
    no-multi-str: 2
    no-native-reassign: 2
    no-new: 2
    no-new-func: 2
    no-new-wrappers: 2
    no-octal-escape: 2
    no-return-assign: 2
    no-script-url: 2
    no-self-compare: 2
    no-sequences: 2
    no-throw-literal: 2
    no-unmodified-loop-condition: 2
    no-unused-expressions: [2, { "allowShortCircuit": true, "allowTernary": true }]
    no-unused-vars: ["error"]
    no-useless-call: 2
    no-useless-concat: 2
    no-var: 2
    no-void: 2
    one-var: 2
    prefer-arrow-callback: 2
    prefer-const: 2
    quotes: [2, "single"]
    semi: 2
    yoda: 2
    import/extensions: 0
    import/no-extraneous-dependencies: 0
    import/prefer-default-export: 0
    space-in-parens: [2, "never"]
    # babel/no-invalid-this: 2
    jsx-a11y/alt-text: 0
    jsx-a11y/label-has-for: 0
    jsx-a11y/anchor-is-valid: 0
    jsx-a11y/no-autofocus: 0
    jsx-a11y/click-events-have-key-events: 0
    jsx-a11y/no-static-element-interactions: 0
    jsx-a11y/no-noninteractive-element-interactions: 0
    react/default-props-match-prop-types: 0
    react/forbid-prop-types: 0
    react/jsx-equals-spacing: 2
    react/jsx-filename-extension: [1, { "extensions": [".js", ".jsx"] }]
    react/jsx-first-prop-new-line: [1, "multiline"]
    react/jsx-indent: [2, 4]
    react/jsx-wrap-multilines:
        - 2
        -
            declaration: parens-new-line
            assignment: parens-new-line
            return: parens-new-line
            arrow: parens-new-line
            prop: ignore
    react/no-array-index-key: 0
    react/prefer-stateless-function: [1, {"ignorePureComponents": true}]
    react/require-default-props: 0

What did you do? Please include the actual source code causing the issue, as well as the command that you used to run ESLint.

Created a minimal example called CustomTextInput-copy.js with only the following code:

const {
    label,
    theme,
    onChangeText,
    containerStyle,
    widget,
    onRef,
    testID,
    height,
    ...restProps
} = this.props;

I run ESLint using

yarn lint:mobile

This command triggers

./node_modules/.bin/eslint src/mobile/

The issue is specifically with no-unused-vars: ["error"]. With this alone, only ...restProps is detected as unused. However, if I provide any argsIgnorePattern, the other unused variables are correctly detected (label, theme, etc). For example, no-unused-vars: ["error", { "argsIgnorePattern": "" }] or no-unused-vars: ["error", { "argsIgnorePattern": "^_" }] will correctly detect the unused variables.

What did you expect to happen?
All unused variables detected

What actually happened? Please include the actual, raw output from ESLint.
Only restProps is detected as unused when no argsIgnorePattern is specified
10:8 error 'restProps' is assigned a value but never used no-unused-vars

Are you willing to submit a pull request to fix this bug?
I'm not sure what's causing this, so I can't submit a PR yet.

[platinumazure]

Hi @rajivshah3, thanks for the issue.

We have a ignoreRestSiblings option which is supposed to let users opt into the behavior you are seeing. Perhaps one of the configs you are extending is setting this property?

Try running ESLint with the --print-config option to see your combined config for the file you are linting. If you see ignoreRestSiblings: true, try setting ignoreRestSiblings: false in your configuration if you don't want that behavior.

We have special behavior when extending from a shareable config and specifying only a lint level (error/warning/off) in your extending config. In that case, the rule options from the extending config are preserved. (Personally, I wish we only did this when using a string configuration rather than an array configuration, since the array configuration is explicitly showing no other options, but that's just how things are right now.)

Hope this helps!

[rajivshah3]

Thanks for the reply @platinumazure . Here's the relevant config from --print-config:

"no-unused-vars": [
      "error",
      {
        "argsIgnorePattern": "^_"
      }
    ],

Interestingly, if I change the config to no-unused-vars: ["error", { "ignoreRestSiblings": false }] (removing argsIgnorePattern and adding ignoreRestSiblings), all unused variables are detected (as expected).

[rajivshah3]

We have special behavior when extending from a shareable config and specifying only a lint level (error/warning/off) in your extending config. In that case, the rule options from the extending config are preserved. (Personally, I wish we only did this when using a string configuration rather than an array configuration, since the array configuration is explicitly showing no other options, but that's just how things are right now.)

Aha, I see what you mean now. When I do print-config with no other options except "error" for no-unused-vars, the ignoreRestSiblings is actually set to true:

"no-unused-vars": [
      "error",
      {
        "vars": "all",
        "args": "after-used",
        "ignoreRestSiblings": true
      }
    ],

Thanks! I'll close this as it's not a bug