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feat(eslint-plugin): new rule method-signature-style (#1685)
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packages/eslint-plugin/docs/rules/method-signature-style.md
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| # Enforces using a particular method signature syntax. (`method-signature-style`) | ||
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| There are two ways to define an object/interface function property. | ||
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| ```ts | ||
| // method shorthand syntax | ||
| interface T1 { | ||
| func(arg: string): number; | ||
| } | ||
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| // regular property with function type | ||
| interface T2 { | ||
| func: (arg: string) => number; | ||
| } | ||
| ``` | ||
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| A good practice is to use the TypeScript's `strict` option (which implies `strictFunctionTypes`) which enables correct typechecking for function properties only (method signatures get old behavior). | ||
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| TypeScript FAQ: | ||
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| > A method and a function property of the same type behave differently. | ||
| > Methods are always bivariant in their argument, while function properties are contravariant in their argument under `strictFunctionTypes`. | ||
| See the reasoning behind that in the [TypeScript PR for the compiler option](https://github.com/microsoft/TypeScript/pull/18654). | ||
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| ## Options | ||
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| This rule accepts one string option: | ||
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| - `"property"`: Enforce using property signature for functions. Use this to enforce maximum correctness together with TypeScript's strict mode. | ||
| - `"method"`: Enforce using method signature for functions. Use this if you aren't using TypeScript's strict mode and prefer this style. | ||
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| The default is `"property"`. | ||
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| ## Rule Details | ||
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| Examples of **incorrect** code with `property` option. | ||
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| ```ts | ||
| interface T1 { | ||
| func(arg: string): number; | ||
| } | ||
| type T2 = { | ||
| func(arg: boolean): void; | ||
| }; | ||
| ``` | ||
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| Examples of **correct** code with `property` option. | ||
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| ```ts | ||
| interface T1 { | ||
| func: (arg: string) => number; | ||
| } | ||
| type T2 = { | ||
| func: (arg: boolean) => void; | ||
| }; | ||
| ``` | ||
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| Examples of **incorrect** code with `method` option. | ||
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| ```ts | ||
| interface T1 { | ||
| func: (arg: string) => number; | ||
| } | ||
| type T2 = { | ||
| func: (arg: boolean) => void; | ||
| }; | ||
| ``` | ||
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| Examples of **correct** code with `method` option. | ||
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| ```ts | ||
| interface T1 { | ||
| func(arg: string): number; | ||
| } | ||
| type T2 = { | ||
| func(arg: boolean): void; | ||
| }; | ||
| ``` | ||
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| ## When Not To Use It | ||
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| If you don't want to enforce a particular style for object/interface function types, and/or if you don't use `strictFunctionTypes`, then you don't need this rule. |
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124
packages/eslint-plugin/src/rules/method-signature-style.ts
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| @@ -0,0 +1,124 @@ | ||
| import { | ||
| AST_NODE_TYPES, | ||
| TSESTree, | ||
| } from '@typescript-eslint/experimental-utils'; | ||
| import * as util from '../util'; | ||
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| export type Options = ['property' | 'method']; | ||
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| export type MessageId = 'errorMethod' | 'errorProperty'; | ||
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| export default util.createRule<Options, MessageId>({ | ||
| name: 'method-signature-style', | ||
| meta: { | ||
| type: 'suggestion', | ||
| docs: { | ||
| description: 'Enforces using a particular method signature syntax.', | ||
| category: 'Best Practices', | ||
| recommended: false, | ||
| }, | ||
| fixable: 'code', | ||
| messages: { | ||
| errorMethod: | ||
| 'Shorthand method signature is forbidden. Use a function property instead.', | ||
| errorProperty: | ||
| 'Function property signature is forbidden. Use a method shorthand instead.', | ||
| }, | ||
| schema: [ | ||
| { | ||
| enum: ['property', 'method'], | ||
| }, | ||
| ], | ||
| }, | ||
| defaultOptions: ['property'], | ||
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| create(context, [mode]) { | ||
| const sourceCode = context.getSourceCode(); | ||
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| function getMethodKey( | ||
| node: TSESTree.TSMethodSignature | TSESTree.TSPropertySignature, | ||
| ): string { | ||
| let key = sourceCode.getText(node.key); | ||
| if (node.computed) { | ||
| key = `[${key}]`; | ||
| } | ||
| if (node.optional) { | ||
| key = `${key}?`; | ||
| } | ||
| if (node.readonly) { | ||
| key = `readonly ${key}`; | ||
| } | ||
| return key; | ||
| } | ||
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| function getMethodParams( | ||
| node: TSESTree.TSMethodSignature | TSESTree.TSFunctionType, | ||
| ): string { | ||
| let params = '()'; | ||
| if (node.params.length > 0) { | ||
| params = sourceCode.text.substring( | ||
| sourceCode.getTokenBefore(node.params[0])!.range[0], | ||
| sourceCode.getTokenAfter(node.params[node.params.length - 1])! | ||
| .range[1], | ||
| ); | ||
| } | ||
| if (node.typeParameters != null) { | ||
| const typeParams = sourceCode.getText(node.typeParameters); | ||
| params = `${typeParams}${params}`; | ||
| } | ||
| return params; | ||
| } | ||
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| function getMethodReturnType( | ||
| node: TSESTree.TSMethodSignature | TSESTree.TSFunctionType, | ||
| ): string { | ||
| return sourceCode.getText(node.returnType!.typeAnnotation); | ||
| } | ||
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| return { | ||
| TSMethodSignature(methodNode): void { | ||
| if (mode === 'method') { | ||
| return; | ||
| } | ||
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| context.report({ | ||
| node: methodNode, | ||
| messageId: 'errorMethod', | ||
| fix: fixer => { | ||
| const key = getMethodKey(methodNode); | ||
| const params = getMethodParams(methodNode); | ||
| const returnType = getMethodReturnType(methodNode); | ||
| return fixer.replaceText( | ||
| methodNode, | ||
| `${key}: ${params} => ${returnType}`, | ||
| ); | ||
| }, | ||
| }); | ||
| }, | ||
| TSPropertySignature(propertyNode): void { | ||
| const typeNode = propertyNode.typeAnnotation?.typeAnnotation; | ||
| if (typeNode?.type !== AST_NODE_TYPES.TSFunctionType) { | ||
| return; | ||
| } | ||
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| if (mode === 'property') { | ||
| return; | ||
| } | ||
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| context.report({ | ||
| node: propertyNode, | ||
| messageId: 'errorProperty', | ||
| fix: fixer => { | ||
| const key = getMethodKey(propertyNode); | ||
| const params = getMethodParams(typeNode); | ||
| const returnType = getMethodReturnType(typeNode); | ||
| return fixer.replaceText( | ||
| propertyNode, | ||
| `${key}${params}: ${returnType}`, | ||
| ); | ||
| }, | ||
| }); | ||
| }, | ||
| }; | ||
| }, | ||
| }); |
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