[no-magic-numbers] - false error report on array destructuring declaration

Tell us about your environment

Node version: v12.12.0 npm version: v6.9.0 Local ESLint version: v6.8.0 (Currently used) Global ESLint version: Not found

What parser (default, Babel-ESLint, etc.) are you using? typescript 3.8 Please show your full configuration:

Configuration

env:
  es2020: true
  browser: true
extends:
  - "eslint:recommended"
  - "plugin:@typescript-eslint/recommended"
  - "plugin:@typescript-eslint/eslint-recommended"
  - "plugin:functional/all"
  - "plugin:jest/recommended"
  - "plugin:react/recommended"
  - "plugin:no-unsanitized/DOM"
  - "prettier"
  - "prettier/@typescript-eslint"
parser: "@typescript-eslint/parser"
parserOptions:
  #  project: "./tsconfig.json"
  sourceType: module
plugins:
  - "@typescript-eslint/eslint-plugin"
  - functional
  - jest
  - no-unsanitized
  - promise
  - react
  - react-hooks
overrides:
  - files:
      - "*.test.js"
      - "*.spec.js"
globals:
  globalThis: "writable"
#  devprint: "readonly"
rules:
  "@typescript-eslint/camelcase": off
  "@typescript-eslint/class-name-casing":
    - off
  "@typescript-eslint/explicit-function-return-type":
    - error
    - allowExpressions: true
  "@typescript-eslint/interface-name-prefix":
    - warn
  "@typescript-eslint/no-empty-interface":
    - error
    - "allowSingleExtends": true
  "@typescript-eslint/no-use-before-define": off
  arrow-body-style: "off"
  arrow-parens: warn
  camelcase: off
  comma-dangle: "off"
  complexity:
    - warn
    - 3
  func-style: warn
  functional/functional-parameters:
    - error
    - enforceParameterCount: false
  functional/immutable-data:
    - error
    - ignorePattern:
        - globalThis
  functional/prefer-readonly-type: off
  functional/no-conditional-statement: off
  functional/no-expression-statement:
    - off
    - ignorePattern:
        - console
        - devprint
        - globalThis
        - render

  functional/no-return-void: off
  id-length:
    - warn
    - {min: 3, exceptions: [_, fn, id, is, BG]}
  id-match:
    - error
    - "^[a-zA-Z_0-9]*$"
    - properties: true
  indent: off
  lines-around-comment:
    - warn
    - ignorePattern: /prettier-ignore/
  max-len:
    - warn
    - code: 90
      comments: 120
      tabWidth: 2
      #      "^\\} from" part is for multi-line imports
      ignorePattern: "Spec|import|^\\} from"
      ignoreUrls: true
  max-lines:
    - warn
    - max: 50
      skipBlankLines: true
  max-params:
    - warn
    - 6
  max-statements:
    - warn
    - 10
  multiline-ternary: "off"
  new-cap: off
  no-console: warn
  no-inline-comments: "off"
  no-magic-numbers:
    - error
    - ignore:
        - 0
        - 1
        - -1
  no-multi-spaces: "off"
  no-param-reassign:
    - error
    - props: true
  no-nested-ternary: "off"
  no-return-await: warn
  no-shadow:
    - error
    - builtinGlobals: true
      allow:
        - "name"
        - "status"
  no-warning-comments: off
  no-undef: error
  no-underscore-dangle:
    - error
    - "allow": ["_id", "_text"]
  no-unneeded-ternary: "off"
  no-unused-vars: warn
  no-use-before-define: "off"
  no-useless-catch: warn
  object-curly-newline: "off"
  one-var: off
  operator-linebreak:
    - warn
    - before
    - overrides:
        +: ignore
        =: ignore
  padding-line-between-statements: "off"
  prefer-destructuring: warn
  radix: "off"
  react/no-string-refs:
    - error
    - noTemplateLiterals: true
  react-hooks/rules-of-hooks: error
  react-hooks/exhaustive-deps: warn
  react/display-name: "off"
  react/prop-types: "off"
  semi: warn
settings: {}

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 [widht, height] = [10, 20];

I use Webstorm's built-in eslint reporting service

What did you expect to happen? No errors reported

What actually happened? Please include the actual, raw output from ESLint. No magic number: 10. (no-magic-numbers)

Are you willing to submit a pull request to fix this bug? noooo…

[yeonjuan]

Thanks for reporting!

• reproduced - Online Demo

In my opinion, It makes sense to treat it as a bug because all numbers are named.

[mdjermanovic]

Something like this might be correct:

/* eslint no-magic-numbers: ["error", { "enforceConst": false }] */

const [a, b] = [1, 2]; // ok

let [a, b] = [1, 2]; // ok

var [a, b] = [1, 2]; // ok

[a, b] = [1, 2]; // error

/* eslint no-magic-numbers: ["error", { "enforceConst": true }] */

const [a, b] = [1, 2]; // ok

let [a, b] = [1, 2]; // error

var [a, b] = [1, 2]; // error

[a, b] = [1, 2]; // error

/* eslint no-magic-numbers: ["error", { "detectObjects": false }] */

[obj.a, obj.b] = [1, 2]; // ok

/* eslint no-magic-numbers: ["error", { "detectObjects": true }] */

[obj.a, obj.b] = [1, 2]; // error

We could find the assignment target for the number, and if it’s a MemberExpression then allow/disallow based on detectObjects.

If it’s an Identifier, then allow only if the assignment is initializing variable (VariableDeclarator, which must be in a const declaration if "enforceConst": true).

Perhaps we could do this for object patterns as well, maybe even support nested destructuring.

There is also proposal #12611 to optionally allow default assignments.