Incorrect no-unused-vars detection

[Zydnar]

environment

• ESLint Version: 6.8.0
• Node Version: 13.1.0
• npm Version: 6.13.0
• yarn Version: 1.19.1

What parser (default, Babel-ESLint, etc.) are you using?
"babel-eslint": "^8.2.3",
But actually error shows after configuring directly eslint with WebStorm, not with babel-eslint.

Please show your full configuration:

Configuration

{// based on https://gist.github.com/nkbt/9efd4facb391edbf8048
  "env": {
    "browser": true,
    "node": true,
    "es6": true
  },
  "parserOptions": {
    "sourceType": "module",
    "ecmaFeatures": {
      "experimentalObjectRestSpread": true
    }
  },
  "parser": "babel-eslint",

  "rules": {

    //
    //Possible Errors
    //
    // The following rules point out areas where you might have made mistakes.
    //
    "comma-dangle": 0, // disallow or enforce trailing commas
    "no-cond-assign": 2, // disallow assignment in conditional expressions
    "no-console": 1, // disallow use of console (off by default in the node environment)
    "no-constant-condition": 2, // disallow use of constant expressions in conditions
    "no-control-regex": 2, // disallow control characters in regular expressions
    "no-debugger": 2, // disallow use of debugger
    "no-dupe-args": 2, // disallow duplicate arguments in functions
    "no-dupe-keys": 2, // disallow duplicate keys when creating object literals
    "no-duplicate-case": 2, // disallow a duplicate case label.
    "no-empty": 2, // disallow empty statements
    //"no-empty-class": 2, // disallow the use of empty character classes in regular expressions
    "no-ex-assign": 2, // disallow assigning to the exception in a catch block
    "no-extra-boolean-cast": 2, // disallow double-negation boolean casts in a boolean context
    "no-extra-parens": 0, // disallow unnecessary parentheses (off by default)
    "no-extra-semi": 2, // disallow unnecessary semicolons
    "no-func-assign": 2, // disallow overwriting functions written as function declarations
    "no-inner-declarations": 2, // disallow function or variable declarations in nested blocks
    "no-invalid-regexp": 2, // disallow invalid regular expression strings in the RegExp constructor
    "no-irregular-whitespace": 2, // disallow irregular whitespace outside of strings and comments
    "no-negated-in-lhs": 2, // disallow negation of the left operand of an in expression
    "no-obj-calls": 2, // disallow the use of object properties of the global object (Math and JSON) as functions
    "no-regex-spaces": 2, // disallow multiple spaces in a regular expression literal
    //"no-reserved-keys": 2, // disallow reserved words being used as object literal keys (off by default)
    "no-sparse-arrays": 2, // disallow sparse arrays
    "no-unreachable": 2, // disallow unreachable statements after a return, throw, continue, or break statement
    "use-isnan": 2, // disallow comparisons with the value NaN
    "valid-jsdoc": 2, // Ensure JSDoc comments are valid (off by default)
    "valid-typeof": 2, // Ensure that the results of typeof are compared against a valid string

    //
    // Best Practices
    //
    // These are rules designed to prevent you from making mistakes.
    // They either prescribe a better way of doing something or help you avoid footguns.
    //
    "block-scoped-var": 0, // treat var statements as if they were block scoped (off by default). 0: deep destructuring is not compatible https://github.com/eslint/eslint/issues/1863
    "complexity": 0, // specify the maximum cyclomatic complexity allowed in a program (off by default)
    "consistent-return": 2, // require return statements to either always or never specify values
    "curly": 2, // specify curly brace conventions for all control statements
    "default-case": 2, // require default case in switch statements (off by default)
    "dot-notation": 2, // encourages use of dot notation whenever possible
    "eqeqeq": 2, // require the use of === and !==
    "guard-for-in": 2, // make sure for-in loops have an if statement (off by default)
    "no-alert": 2, // disallow the use of alert, confirm, and prompt
    "no-caller": 2, // disallow use of arguments.caller or arguments.callee
    "no-div-regex": 2, // disallow division operators explicitly at beginning of regular expression (off by default)
    "no-else-return": 0, // disallow else after a return in an if (off by default)
    //"no-empty-label": 2, // disallow use of labels for anything other then loops and switches
    "no-eq-null": 2, // disallow comparisons to null without a type-checking operator (off by default)
    "no-eval": 2, // disallow use of eval()
    "no-extend-native": 2, // disallow adding to native types
    "no-extra-bind": 2, // disallow unnecessary function binding
    "no-fallthrough": 2, // disallow fallthrough of case statements
    "no-floating-decimal": 2, // disallow the use of leading or trailing decimal points in numeric literals (off by default)
    "no-implied-eval": 2, // disallow use of eval()-like methods
    "no-iterator": 2, // disallow usage of __iterator__ property
    "no-labels": 2, // disallow use of labeled statements
    "no-lone-blocks": 2, // disallow unnecessary nested blocks
    "no-loop-func": 2, // disallow creation of functions within loops
    "no-multi-spaces": 2, // disallow use of multiple spaces
    "no-multi-str": 2, // disallow use of multiline strings
    "no-native-reassign": 2, // disallow reassignments of native objects
    "no-new": 2, // disallow use of new operator when not part of the assignment or comparison
    "no-new-func": 2, // disallow use of new operator for Function object
    "no-new-wrappers": 2, // disallows creating new instances of String,Number, and Boolean
    "no-octal": 2, // disallow use of octal literals
    "no-octal-escape": 2, // disallow use of octal escape sequences in string literals, such as var foo = "Copyright \251";
    "no-param-reassign": 2, // disallow reassignment of function parameters (off by default)
    "no-process-env": 2, // disallow use of process.env (off by default)
    "no-proto": 2, // disallow usage of __proto__ property
    "no-redeclare": 2, // disallow declaring the same variable more then once
    "no-return-assign": 1, // disallow use of assignment in return statement
    "no-script-url": 2, // disallow use of javascript: urls.
    "no-self-compare": 2, // disallow comparisons where both sides are exactly the same (off by default)
    "no-sequences": 2, // disallow use of comma operator
    "no-throw-literal": 2, // restrict what can be thrown as an exception (off by default)
    "no-unused-expressions": 2, // disallow usage of expressions in statement position
    "no-void": 2, // disallow use of void operator (off by default)
    "no-warning-comments": [0, {"terms": ["todo", "fixme"], "location": "start"}], // disallow usage of configurable warning terms in comments": 2, // e.g. TODO or FIXME (off by default)
    "no-with": 2, // disallow use of the with statement
    "radix": 2, // require use of the second argument for parseInt() (off by default)
    "vars-on-top": 2, // requires to declare all vars on top of their containing scope (off by default)
    "wrap-iife": 2, // require immediate function invocation to be wrapped in parentheses (off by default)
    "yoda": 2, // require or disallow Yoda conditions

    //
    // Strict Mode
    //
    // These rules relate to using strict mode.
    //
    "strict": 0, // controls location of Use Strict Directives. 0: required by `babel-eslint`

    //
    // Variables
    //
    // These rules have to do with variable declarations.
    //
    "no-catch-shadow": 2, // disallow the catch clause parameter name being the same as a variable in the outer scope (off by default in the node environment)
    "no-delete-var": 2, // disallow deletion of variables
    "no-label-var": 2, // disallow labels that share a name with a variable
    "no-shadow": 2, // disallow declaration of variables already declared in the outer scope
    "no-shadow-restricted-names": 2, // disallow shadowing of names such as arguments
    "no-undef": 1, // disallow use of undeclared variables unless mentioned in a /*global */ block
    "no-undef-init": 2, // disallow use of undefined when initializing variables
    "no-undefined": 0, // disallow use of undefined variable (off by default)
    "no-unused-vars": 2, // disallow declaration of variables that are not used in the code
    "no-use-before-define": 2, // disallow use of variables before they are defined

    //
    //Stylistic Issues
    //
    // These rules are purely matters of style and are quite subjective.
    //
    "indent": [1, 4, { "SwitchCase": 1, "VariableDeclarator": 1 }], // this option sets a specific tab width for your code (off by default)
    "brace-style": 1, // enforce one true brace style (off by default)
    "camelcase": 1, // require camel case names
    "comma-spacing": [1, {"before": false, "after": true}], // enforce spacing before and after comma
    "comma-style": [1, "last"], // enforce one true comma style (off by default)
    "consistent-this": [1, "_this"], // enforces consistent naming when capturing the current execution context (off by default)
    "eol-last": 1, // enforce newline at the end of file, with no multiple empty lines
    "func-names": 0, // require function expressions to have a name (off by default)
    "func-style": 0, // enforces use of function declarations or expressions (off by default)
    "key-spacing": [1, {"beforeColon": false, "afterColon": true}], // enforces spacing between keys and values in object literal properties
    "max-nested-callbacks": [1, 3], // specify the maximum depth callbacks can be nested (off by default)
    "new-cap": [1, {"newIsCap": true, "capIsNew": false}], // require a capital letter for constructors
    "new-parens": 1, // disallow the omission of parentheses when invoking a constructor with no arguments
    "newline-after-var": 0, // allow/disallow an empty newline after var statement (off by default)
    "no-array-constructor": 1, // disallow use of the Array constructor
    "no-inline-comments": 1, // disallow comments inline after code (off by default)
    "no-lonely-if": 1, // disallow if as the only statement in an else block (off by default)
    "no-mixed-spaces-and-tabs": 1, // disallow mixed spaces and tabs for indentation
    "no-multiple-empty-lines": [1, {"max": 2}], // disallow multiple empty lines (off by default)
    "no-nested-ternary": 1, // disallow nested ternary expressions (off by default)
    "no-new-object": 1, // disallow use of the Object constructor
    "no-spaced-func": 1, // disallow space between function identifier and application
    "no-ternary": 0, // disallow the use of ternary operators (off by default)
    "no-trailing-spaces": 1, // disallow trailing whitespace at the end of lines
    "no-underscore-dangle": 1, // disallow dangling underscores in identifiers
    //"no-wrap-func": 1, // disallow wrapping of non-IIFE statements in parens
    "one-var": [1, "never"], // allow just one var statement per function (off by default)
    "operator-assignment": [0, "never"], // require assignment operator shorthand where possible or prohibit it entirely (off by default)
    "padded-blocks": [0, "never"], // enforce padding within blocks (off by default)
    "quote-props": [1, "as-needed"], // require quotes around object literal property names (off by default)
    "quotes": [0, "single"], // specify whether double or single quotes should be used
    "semi": [1, "always"], // require or disallow use of semicolons instead of ASI
    "semi-spacing": [1, {"before": false, "after": true}], // enforce spacing before and after semicolons
    "sort-vars": 0, // sort variables within the same declaration block (off by default)
    //"space-after-keywords": [1, "always"], // require a space after certain keywords (off by default)
    "space-before-blocks": [1, "always"], // require or disallow space before blocks (off by default)
    "space-before-function-paren": [1, {"anonymous": "always", "named": "never"}], // require or disallow space before function opening parenthesis (off by default)
    //"space-in-brackets": [1, "never"], // require or disallow spaces inside brackets (off by default)
    "space-in-parens": [1, "never"], // require or disallow spaces inside parentheses (off by default)
    //"space-infix-ops": [1, "always"], // require spaces around operators
    //"space-return-throw-case": [1, "always"], // require a space after return, throw, and case
    "space-unary-ops": [1, {"words": true, "nonwords": false}], // Require or disallow spaces before/after unary operators (words on by default, nonwords off by default)
    //"spaced-line-comment": [1, "always"], // require or disallow a space immediately following the // in a line comment (off by default)
    "wrap-regex": 0, // require regex literals to be wrapped in parentheses (off by default)

    //
    // ECMAScript 6
    //
    // These rules are only relevant to ES6 environments and are off by default.
    //
    "no-var": 2, // require let or const instead of var (off by default)
    "generator-star-spacing": [2, "before"], // enforce the spacing around the * in generator functions (off by default)

    //
    // Legacy
    //
    // The following rules are included for compatibility with JSHint and JSLint.
    // While the names of the rules may not match up with the JSHint/JSLint counterpart,
    // the functionality is the same.
    //
    "max-depth": [2, 3], // specify the maximum depth that blocks can be nested (off by default)
    "max-len": [2, 150, 2], // specify the maximum length of a line in your program (off by default)
    "max-params": [2, 5], // limits the number of parameters that can be used in the function declaration. (off by default)
    "max-statements": 0, // specify the maximum number of statement allowed in a function (off by default)
    "no-bitwise": 0, // disallow use of bitwise operators (off by default)
    "no-plusplus": 0 // disallow use of unary operators, ++ and -- (off by default)

  }
}

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

/**
     * Matrix iterator
     *
     * @generator
     * @yield {number} Element of Matrix
     * @return {void}
     */
    [Symbol.iterator] = function *() {
        for (const i of this.state.elements) { // ESLint: 'i' is defined but never used.(no-unused-vars)
            yield i;
        }
    };

/**
     * Checks for GPU limits in WebGL context
     * @return {void}
     */
    queryGPUParameters = ()=>{
        /**
         * @type {WebGLRenderingContext}
         */
        const context = this.state.context;
        const GPUProperties = {};
        for(const i in context) { // ESLint: 'i' is defined but never used.(no-unused-vars)
            // noinspection JSUnfilteredForInLoop
            if(i.slice(0, 3)==='MAX'&&i!=='MAX') {
                // noinspection JSUnfilteredForInLoop
                GPUProperties[i] = context.getParameter(context[i]);
            }
        }
        this.setState({GPUProperties});
    };

What did you expect to happen?
i var shoudn't be marked as not used.

What actually happened? Please include the actual, raw output from ESLint.
i var was marked as unused

[yeonjuan]

@Zydnar
Hi. 😀

But actually error shows after configuring directly eslint with WebStorm, not with babel-eslint.

It is not reproduced in the current version(6.8.0) - default parser.

• Online-Demo-1 - no-error
• Online-Demo-2 - no-error

This is the issue of babel-eslint version, and seems dupe with #12117.
So for fixing this bug, It seems you need to upgrade the babel-eslint version to 10.0.3

[Zydnar]

@yeonjuan It works after upgrade! Sorry for spam and thanks for the solution.

[kaicataldo]

Closing this since the question has been answered.