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feat(eslint-plugin): add eslint rule no-useless-constructor#167
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JamesHenry merged 9 commits intotypescript-eslint:masterfromarmano2:no-useless-constructorFeb 1, 2019
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5e7c3ff feat(eslint-plugin): add eslint rule no-useless-constructor
armano2eeb1dfe docs: correct issue id
armano2f362ecc fix(eslint-plugin): ignore private and protected constructors
armano2643dfd6 fix(eslint-plugin): add additonal test cases and fix formatting
armano2841171c test(eslint-plugin): fix issue in test case
armano2bafe080 docs(eslint-plugin): add example of valid ts code
armano2a06d950 fix(eslint-plugin): improve detection of useless constructors
armano229d44f4 Merge branch 'master' into no-useless-constructor
armano2fbb9586 Merge branch 'master' into no-useless-constructor
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3 changes: 2 additions & 1 deletionpackages/eslint-plugin/README.md
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78 changes: 78 additions & 0 deletionspackages/eslint-plugin/docs/rules/no-useless-constructor.md
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,78 @@ | ||
| # Disallow unnecessary constructors (no-useless-constructor) | ||
| ES2015 provides a default class constructor if one is not specified. As such, it is unnecessary to provide an empty constructor or one that simply delegates into its parent class, as in the following examples: | ||
| ```js | ||
| class A { | ||
| constructor() {} | ||
| } | ||
| class A extends B { | ||
| constructor(value) { | ||
| super(value); | ||
| } | ||
| } | ||
| ``` | ||
| ## Rule Details | ||
| This rule flags class constructors that can be safely removed without changing how the class works. | ||
| ## Examples | ||
| Examples of **incorrect** code for this rule: | ||
| ```js | ||
| /*eslint no-useless-constructor: "error"*/ | ||
| class A { | ||
| constructor() {} | ||
| } | ||
| class A extends B { | ||
| constructor(...args) { | ||
| super(...args); | ||
| } | ||
| } | ||
| ``` | ||
| Examples of **correct** code for this rule: | ||
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| ```js | ||
| /*eslint no-useless-constructor: "error"*/ | ||
| class A {} | ||
| class A { | ||
| constructor() { | ||
| doSomething(); | ||
| } | ||
| } | ||
| class A extends B { | ||
| constructor() { | ||
| super('foo'); | ||
| } | ||
| } | ||
| class A extends B { | ||
| constructor() { | ||
| super(); | ||
| doSomething(); | ||
| } | ||
| } | ||
| class A extends B { | ||
| constructor(protected name: string) {} | ||
| } | ||
| class A extends B { | ||
| protected constructor() {} | ||
| } | ||
| ``` | ||
| ## When Not To Use It | ||
| If you don't want to be notified about unnecessary constructors, you can safely disable this rule. | ||
| <sup>Taken with ❤️ [from ESLint core](https://github.com/eslint/eslint/blob/master/docs/rules/no-useless-constructor.md)</sup> | ||
80 changes: 80 additions & 0 deletionspackages/eslint-plugin/lib/rules/no-useless-constructor.js
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,80 @@ | ||
| /** | ||
| * @fileoverview Disallow unnecessary constructors | ||
| * @author Armano <https://github.com/armano2> | ||
| */ | ||
| 'use strict'; | ||
| const baseRule = require('eslint/lib/rules/no-useless-constructor'); | ||
| const util = require('../util'); | ||
| //------------------------------------------------------------------------------ | ||
| // Rule Definition | ||
| //------------------------------------------------------------------------------ | ||
| /** | ||
| * Check if method with accessibility is not useless | ||
| * @param {MethodDefinition} node | ||
| * @returns {boolean} | ||
| */ | ||
| function checkAccessibility(node) { | ||
| switch (node.accessibility) { | ||
| case 'protected': | ||
| case 'private': | ||
| return false; | ||
| case 'public': | ||
| if ( | ||
| node.parent.type === 'ClassBody' && | ||
| node.parent.parent && | ||
| node.parent.parent.superClass | ||
| ) { | ||
| return false; | ||
| } | ||
| break; | ||
| } | ||
| return true; | ||
| } | ||
| /** | ||
| * Check if method is not unless due to typescript parameter properties | ||
| * @param {MethodDefinition} node | ||
| * @returns {boolean} | ||
| */ | ||
| function checkParams(node) { | ||
| return ( | ||
| !node.value.params || | ||
| !node.value.params.some(param => param.type === 'TSParameterProperty') | ||
| ); | ||
| } | ||
| module.exports = Object.assign({}, baseRule, { | ||
| meta: { | ||
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| type: 'problem', | ||
| docs: { | ||
| description: 'Disallow unnecessary constructors', | ||
| category: 'ECMAScript 6', | ||
| url: util.metaDocsUrl('no-useless-constructor') | ||
| }, | ||
| schema: baseRule.meta.schema, | ||
| messages: baseRule.meta.messages | ||
| }, | ||
| create(context) { | ||
| const rules = baseRule.create(context); | ||
| //---------------------------------------------------------------------- | ||
| // Public | ||
| //---------------------------------------------------------------------- | ||
| return { | ||
| MethodDefinition(node) { | ||
| if ( | ||
| node.value && | ||
| node.value.type === 'FunctionExpression' && | ||
| checkAccessibility(node) && | ||
| checkParams(node) | ||
| ) { | ||
| rules.MethodDefinition(node); | ||
| } | ||
| } | ||
| }; | ||
| } | ||
| }); | ||
100 changes: 100 additions & 0 deletionspackages/eslint-plugin/tests/lib/rules/no-useless-constructor.js
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,100 @@ | ||
| 'use strict'; | ||
| //------------------------------------------------------------------------------ | ||
| // Requirements | ||
| //------------------------------------------------------------------------------ | ||
| const rule = require('../../../lib/rules/no-useless-constructor'), | ||
| RuleTester = require('eslint').RuleTester; | ||
| const ruleTester = new RuleTester({ | ||
| parserOptions: { | ||
| ecmaVersion: 6, | ||
| sourceType: 'module' | ||
| }, | ||
| parser: '@typescript-eslint/parser' | ||
| }); | ||
| const error = { message: 'Useless constructor.', type: 'MethodDefinition' }; | ||
| ruleTester.run('no-useless-constructor', rule, { | ||
| valid: [ | ||
| 'class A { }', | ||
| 'class A { constructor(){ doSomething(); } }', | ||
| 'class A extends B { constructor(){} }', | ||
| "class A extends B { constructor(){ super('foo'); } }", | ||
| 'class A extends B { constructor(foo, bar){ super(foo, bar, 1); } }', | ||
| 'class A extends B { constructor(){ super(); doSomething(); } }', | ||
| 'class A extends B { constructor(...args){ super(...args); doSomething(); } }', | ||
| 'class A { dummyMethod(){ doSomething(); } }', | ||
| 'class A extends B.C { constructor() { super(foo); } }', | ||
| 'class A extends B.C { constructor([a, b, c]) { super(...arguments); } }', | ||
| 'class A extends B.C { constructor(a = f()) { super(...arguments); } }', | ||
| 'class A extends B { constructor(a, b, c) { super(a, b); } }', | ||
| 'class A extends B { constructor(foo, bar){ super(foo); } }', | ||
| 'class A extends B { constructor(test) { super(); } }', | ||
| 'class A extends B { constructor() { foo; } }', | ||
| 'class A extends B { constructor(foo, bar) { super(bar); } }', | ||
| // https://github.com/typescript-eslint/typescript-eslint/issues/15 | ||
| 'declare class A { constructor(); }', | ||
| 'class A { constructor(); }', | ||
| 'abstract class A { constructor(); }', | ||
| 'abstract class A { abstract constructor(); }', | ||
| // https://github.com/typescript-eslint/typescript-eslint/issues/48 | ||
| 'class A { constructor(private name: string) {} }', | ||
| 'class A { constructor(public name: string) {} }', | ||
| 'class A { constructor(protected name: string) {} }', | ||
| // https://github.com/typescript-eslint/typescript-eslint/pull/167#discussion_r252638401 | ||
| 'class A { private constructor() {} }', | ||
| 'class A { protected constructor() {} }', | ||
| 'class A extends B { public constructor() {} }', | ||
| 'class A extends B { protected constructor(foo, bar) { super(bar); } }', | ||
| 'class A extends B { private constructor(foo, bar) { super(bar); } }', | ||
| 'class A extends B { public constructor(foo){ super(foo); } }', | ||
| 'class A extends B { public constructor(foo){} }' | ||
| ], | ||
| invalid: [ | ||
| { | ||
| code: 'class A { constructor(){} }', | ||
| errors: [error] | ||
| }, | ||
| { | ||
| code: "class A { 'constructor'(){} }", | ||
| errors: [error] | ||
| }, | ||
| { | ||
| code: 'class A extends B { constructor() { super(); } }', | ||
| errors: [error] | ||
| }, | ||
| { | ||
| code: 'class A extends B { constructor(foo){ super(foo); } }', | ||
| errors: [error] | ||
| }, | ||
| { | ||
| code: 'class A extends B { constructor(foo, bar){ super(foo, bar); } }', | ||
| errors: [error] | ||
| }, | ||
| { | ||
| code: 'class A extends B { constructor(...args){ super(...args); } }', | ||
| errors: [error] | ||
| }, | ||
| { | ||
| code: 'class A extends B.C { constructor() { super(...arguments); } }', | ||
| errors: [error] | ||
| }, | ||
| { | ||
| code: | ||
| 'class A extends B { constructor(a, b, ...c) { super(...arguments); } }', | ||
| errors: [error] | ||
| }, | ||
| { | ||
| code: | ||
| 'class A extends B { constructor(a, b, ...c) { super(a, b, ...c); } }', | ||
| errors: [error] | ||
| }, | ||
| { | ||
| code: 'class A { public constructor() {} }', | ||
| errors: [error] | ||
| } | ||
| ] | ||
| }); |
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