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feat(eslint-plugin): add prefer-function-type rule (#222)
feat(eslint-plugin): add prefer-function-type rule
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,57 @@ | ||
| # Use function types instead of interfaces with call signatures (prefer-function-type) | ||
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| ## Rule Details | ||
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| This rule suggests using a function type instead of an interface or object type literal with a single call signature. | ||
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| Examples of **incorrect** code for this rule: | ||
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| ```ts | ||
| interface Foo { | ||
| (): string; | ||
| } | ||
| ``` | ||
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| ```ts | ||
| function foo(bar: { (): number }): number { | ||
| return bar(); | ||
| } | ||
| ``` | ||
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| ```ts | ||
| interface Foo extends Function { | ||
| (): void; | ||
| } | ||
| ``` | ||
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| Examples of **correct** code for this rule: | ||
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| ```ts | ||
| interface Foo { | ||
| (): void; | ||
| bar: number; | ||
| } | ||
| ``` | ||
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| ```ts | ||
| function foo(bar: { (): string; baz: number }): string { | ||
| return bar(); | ||
| } | ||
| ``` | ||
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| ```ts | ||
| interface Foo { | ||
| bar: string; | ||
| } | ||
| interface Bar extends Foo { | ||
| (): void; | ||
| } | ||
| ``` | ||
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| ## When Not To Use It | ||
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| If you specifically want to use an interface or type literal with a single call signature for stylistic reasons, you can disable this rule. | ||
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| ## Further Reading | ||
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| - TSLint: [`callable-types`](https://palantir.github.io/tslint/rules/callable-types/) |
171 changes: 171 additions & 0 deletions
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packages/eslint-plugin/lib/rules/prefer-function-type.js
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,171 @@ | ||
| /** | ||
| * @fileoverview Use function types instead of interfaces with call signatures | ||
| * @author Benjamin Lichtman | ||
| */ | ||
| 'use strict'; | ||
| const util = require('../util'); | ||
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| /** | ||
| * @typedef {import("eslint").Rule.RuleModule} RuleModule | ||
| * @typedef {import("estree").Node} ESTreeNode | ||
| */ | ||
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| //------------------------------------------------------------------------------ | ||
| // Rule Definition | ||
| //------------------------------------------------------------------------------ | ||
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| /** | ||
| * @type {RuleModule} | ||
| */ | ||
| module.exports = { | ||
| meta: { | ||
| docs: { | ||
| description: | ||
| 'Use function types instead of interfaces with call signatures', | ||
| category: 'TypeScript', | ||
| recommended: false, | ||
| extraDescription: [util.tslintRule('prefer-function-type')], | ||
| url: util.metaDocsUrl('prefer-function-type') | ||
| }, | ||
| fixable: 'code', | ||
| messages: { | ||
| functionTypeOverCallableType: | ||
| "{{ type }} has only a call signature - use '{{ sigSuggestion }}' instead." | ||
| }, | ||
| schema: [], | ||
| type: 'suggestion' | ||
| }, | ||
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| create(context) { | ||
| const sourceCode = context.getSourceCode(); | ||
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| //---------------------------------------------------------------------- | ||
| // Helpers | ||
| //---------------------------------------------------------------------- | ||
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| /** | ||
| * Checks if there is no supertype or if the supertype is 'Function' | ||
| * @param {ESTreeNode} node The node being checked | ||
| * @returns {boolean} Returns true iff there is no supertype or if the supertype is 'Function' | ||
| */ | ||
| function noSupertype(node) { | ||
| if (!node.extends || node.extends.length === 0) { | ||
| return true; | ||
| } | ||
| if (node.extends.length !== 1) { | ||
| return false; | ||
| } | ||
| const expr = node.extends[0].expression; | ||
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| return expr.type === 'Identifier' && expr.name === 'Function'; | ||
| } | ||
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| /** | ||
| * @param {ESTreeNode} parent The parent of the call signature causing the diagnostic | ||
| * @returns {boolean} true iff the parent node needs to be wrapped for readability | ||
| */ | ||
| function shouldWrapSuggestion(parent) { | ||
| switch (parent.type) { | ||
| case 'TSUnionType': | ||
| case 'TSIntersectionType': | ||
| case 'TSArrayType': | ||
| return true; | ||
| default: | ||
| return false; | ||
| } | ||
| } | ||
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| /** | ||
| * @param {ESTreeNode} call The call signature causing the diagnostic | ||
| * @param {ESTreeNode} parent The parent of the call | ||
| * @returns {string} The suggestion to report | ||
| */ | ||
| function renderSuggestion(call, parent) { | ||
| const start = call.range[0]; | ||
| const colonPos = call.returnType.range[0] - start; | ||
| const text = sourceCode.getText().slice(start, call.range[1]); | ||
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| let suggestion = `${text.slice(0, colonPos)} =>${text.slice( | ||
| colonPos + 1 | ||
| )}`; | ||
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| if (shouldWrapSuggestion(parent.parent)) { | ||
| suggestion = `(${suggestion})`; | ||
| } | ||
| if (parent.type === 'TSInterfaceDeclaration') { | ||
| if (typeof parent.typeParameters !== 'undefined') { | ||
| return `type ${sourceCode | ||
| .getText() | ||
| .slice( | ||
| parent.id.range[0], | ||
| parent.typeParameters.range[1] | ||
| )} = ${suggestion}`; | ||
| } | ||
| return `type ${parent.id.name} = ${suggestion}`; | ||
| } | ||
| return suggestion.endsWith(';') ? suggestion.slice(0, -1) : suggestion; | ||
| } | ||
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| /** | ||
| * @param {ESTreeNode} member The TypeElement being checked | ||
| * @param {ESTreeNode} node The parent of member being checked | ||
| * @returns {void} | ||
| */ | ||
| function checkMember(member, node) { | ||
| if ( | ||
| (member.type === 'TSCallSignatureDeclaration' || | ||
| member.type === 'TSConstructSignatureDeclaration') && | ||
| typeof member.returnType !== 'undefined' | ||
| ) { | ||
| const suggestion = renderSuggestion(member, node); | ||
| const fixStart = | ||
| node.type === 'TSTypeLiteral' | ||
| ? node.range[0] | ||
| : sourceCode | ||
| .getTokens(node) | ||
| .filter( | ||
| token => | ||
| token.type === 'Keyword' && token.value === 'interface' | ||
| )[0].range[0]; | ||
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| context.report({ | ||
| node: member, | ||
| messageId: 'functionTypeOverCallableType', | ||
| data: { | ||
| type: node.type === 'TSTypeLiteral' ? 'Type literal' : 'Interface', | ||
| sigSuggestion: suggestion | ||
| }, | ||
| fix(fixer) { | ||
| return fixer.replaceTextRange( | ||
| [fixStart, node.range[1]], | ||
| suggestion | ||
| ); | ||
| } | ||
| }); | ||
| } | ||
| } | ||
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| //---------------------------------------------------------------------- | ||
| // Public | ||
| //---------------------------------------------------------------------- | ||
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| return { | ||
| /** | ||
| * @param {TSInterfaceDeclaration} node The node being checked | ||
| * @returns {void} | ||
| */ | ||
| TSInterfaceDeclaration(node) { | ||
| if (noSupertype(node) && node.body.body.length === 1) { | ||
| checkMember(node.body.body[0], node); | ||
| } | ||
| }, | ||
| /** | ||
| * @param {TSTypeLiteral} node The node being checked | ||
| * @returns {void} | ||
| */ | ||
| 'TSTypeLiteral[members.length = 1]'(node) { | ||
| checkMember(node.members[0], node); | ||
| } | ||
| }; | ||
| } | ||
| }; |
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