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[FEAT] [no-unnecessary-class] Add rule (typescript-eslint#234)
* Add `no-unnecessary-class` rule * Add metadata * ⬆️ eslint-docs
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packages/eslint-plugin-typescript/docs/rules/no-extraneous-class.md
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| # Forbids the use of classes as namespaces (no-extraneous-class) | ||
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| This rule warns when a class is accidentally used as a namespace. | ||
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| ## Rule Details | ||
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| From TSLint’s docs: | ||
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| > Users who come from a Java-style OO language may wrap their utility functions in an extra class, | ||
| > instead of putting them at the top level. | ||
| Examples of **incorrect** code for this rule: | ||
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| ```ts | ||
| class EmptyClass {} | ||
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| class ConstructorOnly { | ||
| constructor() { | ||
| foo(); | ||
| } | ||
| } | ||
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| // Use an object instead: | ||
| class StaticOnly { | ||
| static version = 42; | ||
| static hello() { | ||
| console.log("Hello, world!"); | ||
| } | ||
| } | ||
| ``` | ||
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| Examples of **correct** code for this rule: | ||
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| ```ts | ||
| class EmptyClass extends SuperClass {} | ||
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| class ParameterProperties { | ||
| constructor(public name: string) {} | ||
| } | ||
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| const StaticOnly = { | ||
| version: 42, | ||
| hello() { | ||
| console.log("Hello, world!"); | ||
| }, | ||
| }; | ||
| ``` | ||
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| ### Options | ||
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| This rule accepts a single object option. | ||
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| - `constructorOnly: true` will silence warnings about classes containing only a constructor. | ||
| - `allowEmpty: true` will silence warnings about empty classes. | ||
| - `staticOnly: true` will silence warnings about classes containing only static members. | ||
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| ## When Not To Use It | ||
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| You can disable this rule if you don’t have anyone who would make these kinds of mistakes on your | ||
| team or if you use classes as namespaces. | ||
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| ## Compatibility | ||
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| [`no-unnecessary-class`](https://palantir.github.io/tslint/rules/no-unnecessary-class/) from TSLint |
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packages/eslint-plugin-typescript/lib/rules/no-extraneous-class.js
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| /** | ||
| * @fileoverview Forbids the use of classes as namespaces | ||
| * @author Jed Fox | ||
| */ | ||
| "use strict"; | ||
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| const util = require("../util"); | ||
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| //------------------------------------------------------------------------------ | ||
| // Rule Definition | ||
| //------------------------------------------------------------------------------ | ||
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| module.exports = { | ||
| meta: { | ||
| docs: { | ||
| description: "Forbids the use of classes as namespaces", | ||
| extraDescription: [util.tslintRule("no-unnecessary-class")], | ||
| category: "Best Practices", | ||
| recommended: false, | ||
| url: util.metaDocsUrl("no-extraneous-class"), | ||
| }, | ||
| fixable: null, | ||
| schema: [ | ||
| { | ||
| type: "object", | ||
| additionalProperties: false, | ||
| properties: { | ||
| allowConstructorOnly: { | ||
| type: "boolean", | ||
| }, | ||
| allowEmpty: { | ||
| type: "boolean", | ||
| }, | ||
| allowStaticOnly: { | ||
| type: "boolean", | ||
| }, | ||
| }, | ||
| }, | ||
| ], | ||
| messages: { | ||
| empty: "Unexpected empty class.", | ||
| onlyStatic: "Unexpected class with only static properties.", | ||
| onlyConstructor: "Unexpected class with only a constructor.", | ||
| }, | ||
| }, | ||
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| create(context) { | ||
| const { allowConstructorOnly, allowEmpty, allowStaticOnly } = | ||
| context.options[0] || {}; | ||
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| return { | ||
| ClassBody(node) { | ||
| const { id, superClass } = node.parent; | ||
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| if (superClass) return; | ||
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| if (node.body.length === 0) { | ||
| if (allowEmpty) return; | ||
| context.report({ node: id, messageId: "empty" }); | ||
| return; | ||
| } | ||
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| let onlyStatic = true; | ||
| let onlyConstructor = true; | ||
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| for (const prop of node.body) { | ||
| if (prop.kind === "constructor") { | ||
| if ( | ||
| prop.value.params.some( | ||
| param => param.type === "TSParameterProperty" | ||
| ) | ||
| ) { | ||
| onlyConstructor = false; | ||
| onlyStatic = false; | ||
| } | ||
| } else { | ||
| onlyConstructor = false; | ||
| if (!prop.static) { | ||
| onlyStatic = false; | ||
| } | ||
| } | ||
| if (!(onlyStatic || onlyConstructor)) break; | ||
| } | ||
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| if (onlyConstructor) { | ||
| if (!allowConstructorOnly) { | ||
| context.report({ | ||
| node: id, | ||
| messageId: "onlyConstructor", | ||
| }); | ||
| } | ||
| return; | ||
| } | ||
| if (onlyStatic && !allowStaticOnly) { | ||
| context.report({ node: id, messageId: "onlyStatic" }); | ||
| } | ||
| }, | ||
| }; | ||
| }, | ||
| }; |
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packages/eslint-plugin-typescript/tests/lib/rules/no-extraneous-class.js
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| /** | ||
| * @fileoverview Forbids the use of classes as namespaces | ||
| * Some tests adapted from https://github.com/palantir/tslint/tree/c7fc99b5/test/rules/no-unnecessary-class | ||
| * @author Jed Fox | ||
| */ | ||
| "use strict"; | ||
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| //------------------------------------------------------------------------------ | ||
| // Requirements | ||
| //------------------------------------------------------------------------------ | ||
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| const rule = require("../../../lib/rules/no-extraneous-class"), | ||
| RuleTester = require("eslint").RuleTester; | ||
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| const empty = { messageId: "empty", type: "Identifier" }; | ||
| const onlyStatic = { messageId: "onlyStatic", type: "Identifier" }; | ||
| const onlyConstructor = { messageId: "onlyConstructor", type: "Identifier" }; | ||
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| //------------------------------------------------------------------------------ | ||
| // Tests | ||
| //------------------------------------------------------------------------------ | ||
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| const ruleTester = new RuleTester({ | ||
| parser: "typescript-eslint-parser", | ||
| }); | ||
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| ruleTester.run("no-extraneous-class", rule, { | ||
| valid: [ | ||
| ` | ||
| class Foo { | ||
| public prop = 1; | ||
| constructor() {} | ||
| } | ||
| `.trim(), | ||
| ` | ||
| export class CClass extends BaseClass { | ||
| public static helper(): void {} | ||
| private static privateHelper(): boolean { | ||
| return true; | ||
| } | ||
| constructor() {} | ||
| } | ||
| `.trim(), | ||
| ` | ||
| class Foo { | ||
| constructor( | ||
| public bar: string | ||
| ) {} | ||
| } | ||
| `.trim(), | ||
| { | ||
| code: "class Foo {}", | ||
| options: [{ allowEmpty: true }], | ||
| }, | ||
| { | ||
| code: ` | ||
| class Foo { | ||
| constructor() {} | ||
| } | ||
| `.trim(), | ||
| options: [{ allowConstructorOnly: true }], | ||
| }, | ||
| { | ||
| code: ` | ||
| export class Bar { | ||
| public static helper(): void {} | ||
| private static privateHelper(): boolean { | ||
| return true; | ||
| } | ||
| } | ||
| `.trim(), | ||
| options: [{ allowStaticOnly: true }], | ||
| }, | ||
| ], | ||
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| invalid: [ | ||
| { | ||
| code: "class Foo {}", | ||
| errors: [empty], | ||
| }, | ||
| { | ||
| code: ` | ||
| class Foo { | ||
| public prop = 1; | ||
| constructor() { | ||
| class Bar { | ||
| static PROP = 2; | ||
| } | ||
| } | ||
| } | ||
| export class Bar { | ||
| public static helper(): void {} | ||
| private static privateHelper(): boolean { | ||
| return true; | ||
| } | ||
| } | ||
| `.trim(), | ||
| errors: [onlyStatic, onlyStatic], | ||
| }, | ||
| { | ||
| code: ` | ||
| class Foo { | ||
| constructor() {} | ||
| } | ||
| `.trim(), | ||
| errors: [onlyConstructor], | ||
| }, | ||
| { | ||
| code: ` | ||
| export class AClass { | ||
| public static helper(): void {} | ||
| private static privateHelper(): boolean { | ||
| return true; | ||
| } | ||
| constructor() { | ||
| class nestedClass { | ||
| } | ||
| } | ||
| } | ||
| `.trim(), | ||
| errors: [onlyStatic, empty], | ||
| }, | ||
| ], | ||
| }); |
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