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feat(eslint-plugin): [no-import-type-side-effects] add rule to warn a…
…gainst runtime side effects with `verbatimModuleSyntax` (#6394)
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packages/eslint-plugin/docs/rules/no-import-type-side-effects.md
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| --- | ||
| description: 'Enforce the use of top-level import type qualifier when an import only has specifiers with inline type qualifiers.' | ||
| --- | ||
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| > 🛑 This file is source code, not the primary documentation location! 🛑 | ||
| > | ||
| > See **https://typescript-eslint.io/rules/no-import-type-side-effects** for documentation. | ||
| The [`--verbatimModuleSyntax`](https://www.typescriptlang.org/tsconfig#verbatimModuleSyntax) compiler option causes TypeScript to do simple and predictable transpilation on import declarations. | ||
| Namely, it completely removes import declarations with a top-level `type` qualifier, and it removes any import specifiers with an inline `type` qualifier. | ||
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| The latter behavior does have one potentially surprising effect in that in certain cases TS can leave behind a "side effect" import at runtime: | ||
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| ```ts | ||
| import { type A, type B } from 'mod'; | ||
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| // is transpiled to | ||
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| import {} from 'mod'; | ||
| // which is the same as | ||
| import 'mod'; | ||
| ``` | ||
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| For the rare case of needing to import for side effects, this may be desirable - but for most cases you will not want to leave behind an unnecessary side effect import. | ||
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| ## Examples | ||
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| This rule enforces that you use a top-level `type` qualifier for imports when it only imports specifiers with an inline `type` qualifier | ||
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| <!--tabs--> | ||
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| ### ❌ Incorrect | ||
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| ```ts | ||
| import { type A } from 'mod'; | ||
| import { type A as AA } from 'mod'; | ||
| import { type A, type B } from 'mod'; | ||
| import { type A as AA, type B as BB } from 'mod'; | ||
| ``` | ||
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| ### ✅ Correct | ||
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| ```ts | ||
| import type { A } from 'mod'; | ||
| import type { A as AA } from 'mod'; | ||
| import type { A, B } from 'mod'; | ||
| import type { A as AA, B as BB } from 'mod'; | ||
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| import T from 'mod'; | ||
| import type T from 'mod'; | ||
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| import * as T from 'mod'; | ||
| import type * as T from 'mod'; | ||
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| import { T } from 'mod'; | ||
| import type { T } from 'mod'; | ||
| import { T, U } from 'mod'; | ||
| import type { T, U } from 'mod'; | ||
| import { type T, U } from 'mod'; | ||
| import { T, type U } from 'mod'; | ||
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| import type T, { U } from 'mod'; | ||
| import T, { type U } from 'mod'; | ||
| ``` | ||
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| ## When Not To Use It | ||
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| - If you want to leave behind side effect imports, then you shouldn't use this rule. | ||
| - If you're not using TypeScript 5.0's `verbatimModuleSyntax` option, then you don't need this rule. | ||
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| ## Related To | ||
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| - [`consistent-type-imports`](./consistent-type-imports.md) | ||
| - [`import/consistent-type-specifier-style`](https://github.com/import-js/eslint-plugin-import/blob/main/docs/rules/consistent-type-specifier-style.md) | ||
| - [`import/no-duplicates` with `{"prefer-inline": true}`](https://github.com/import-js/eslint-plugin-import/blob/main/docs/rules/no-duplicates.md#inline-type-imports) |
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76 changes: 76 additions & 0 deletions
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packages/eslint-plugin/src/rules/no-import-type-side-effects.ts
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|---|---|---|
| @@ -0,0 +1,76 @@ | ||
| import type { TSESLint, TSESTree } from '@typescript-eslint/utils'; | ||
| import { AST_NODE_TYPES } from '@typescript-eslint/utils'; | ||
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| import * as util from '../util'; | ||
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| type Options = []; | ||
| type MessageIds = 'useTopLevelQualifier'; | ||
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| export default util.createRule<Options, MessageIds>({ | ||
| name: 'no-import-type-side-effects', | ||
| meta: { | ||
| type: 'problem', | ||
| docs: { | ||
| description: | ||
| 'Enforce the use of top-level import type qualifier when an import only has specifiers with inline type qualifiers', | ||
| recommended: false, | ||
| }, | ||
| fixable: 'code', | ||
| messages: { | ||
| useTopLevelQualifier: | ||
| 'TypeScript will only remove the inline type specifiers which will leave behind a side effect import at runtime. Convert this to a top-level type qualifier to properly remove the entire import.', | ||
| }, | ||
| schema: [], | ||
| }, | ||
| defaultOptions: [], | ||
| create(context) { | ||
| const sourceCode = context.getSourceCode(); | ||
| return { | ||
| 'ImportDeclaration[importKind!="type"]'( | ||
| node: TSESTree.ImportDeclaration, | ||
| ): void { | ||
| const specifiers: TSESTree.ImportSpecifier[] = []; | ||
| for (const specifier of node.specifiers) { | ||
| if ( | ||
| specifier.type !== AST_NODE_TYPES.ImportSpecifier || | ||
| specifier.importKind !== 'type' | ||
| ) { | ||
| return; | ||
| } | ||
| specifiers.push(specifier); | ||
| } | ||
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| context.report({ | ||
| node, | ||
| messageId: 'useTopLevelQualifier', | ||
| fix(fixer) { | ||
| const fixes: TSESLint.RuleFix[] = []; | ||
| for (const specifier of specifiers) { | ||
| const qualifier = util.nullThrows( | ||
| sourceCode.getFirstToken(specifier, util.isTypeKeyword), | ||
| util.NullThrowsReasons.MissingToken( | ||
| 'type keyword', | ||
| 'import specifier', | ||
| ), | ||
| ); | ||
| fixes.push( | ||
| fixer.removeRange([ | ||
| qualifier.range[0], | ||
| specifier.imported.range[0], | ||
| ]), | ||
| ); | ||
| } | ||
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| const importKeyword = util.nullThrows( | ||
| sourceCode.getFirstToken(node, util.isImportKeyword), | ||
| util.NullThrowsReasons.MissingToken('import keyword', 'import'), | ||
| ); | ||
| fixes.push(fixer.insertTextAfter(importKeyword, ' type')); | ||
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| return fixes; | ||
| }, | ||
| }); | ||
| }, | ||
| }; | ||
| }, | ||
| }); |
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packages/eslint-plugin/tests/rules/no-import-type-side-effects.test.ts
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| import rule from '../../src/rules/no-import-type-side-effects'; | ||
| import { RuleTester } from '../RuleTester'; | ||
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| const ruleTester = new RuleTester({ | ||
| parser: '@typescript-eslint/parser', | ||
| }); | ||
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| ruleTester.run('no-import-type-side-effects', rule, { | ||
| valid: [ | ||
| "import T from 'mod';", | ||
| "import * as T from 'mod';", | ||
| "import { T } from 'mod';", | ||
| "import type { T } from 'mod';", | ||
| "import type { T, U } from 'mod';", | ||
| "import { type T, U } from 'mod';", | ||
| "import { T, type U } from 'mod';", | ||
| "import type T from 'mod';", | ||
| "import type T, { U } from 'mod';", | ||
| "import T, { type U } from 'mod';", | ||
| "import type * as T from 'mod';", | ||
| ], | ||
| invalid: [ | ||
| { | ||
| code: "import { type A } from 'mod';", | ||
| output: "import type { A } from 'mod';", | ||
| errors: [{ messageId: 'useTopLevelQualifier' }], | ||
| }, | ||
| { | ||
| code: "import { type A as AA } from 'mod';", | ||
| output: "import type { A as AA } from 'mod';", | ||
| errors: [{ messageId: 'useTopLevelQualifier' }], | ||
| }, | ||
| { | ||
| code: "import { type A, type B } from 'mod';", | ||
| output: "import type { A, B } from 'mod';", | ||
| errors: [{ messageId: 'useTopLevelQualifier' }], | ||
| }, | ||
| { | ||
| code: "import { type A as AA, type B as BB } from 'mod';", | ||
| output: "import type { A as AA, B as BB } from 'mod';", | ||
| errors: [{ messageId: 'useTopLevelQualifier' }], | ||
| }, | ||
| ], | ||
| }); |
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