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Add require-module-specifiers rule (#2686)
Co-authored-by: Sindre Sorhus <[email protected]>
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‎docs/rules/require-module-specifiers.md

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# Require non-empty specifier list in import and export statements
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💼 This rule is enabled in the ✅ `recommended` [config](https://github.com/sindresorhus/eslint-plugin-unicorn#recommended-config).
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🔧💡 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix) and manually fixable by [editor suggestions](https://eslint.org/docs/latest/use/core-concepts#rule-suggestions).
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<!-- end auto-generated rule header -->
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<!-- Do not manually modify this header. Run: `npm run fix:eslint-docs` -->
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Enforce non-empty specifier list in `import` and `export` statements. Use a [side-effect import](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import#import_a_module_for_its_side_effects_only) if needed, or remove the statement.
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## Examples
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```js
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// ❌
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import {} from 'foo';
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// ✅
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import 'foo';
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```
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```js
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// ❌
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import foo, {} from 'foo';
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// ✅
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import foo from 'foo';
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```
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```js
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// ❌
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export {} from 'foo';
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// ✅
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import 'foo';
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```
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```js
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// ❌
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export {}
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```

‎readme.md

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| [prevent-abbreviations](docs/rules/prevent-abbreviations.md) | Prevent abbreviations. | ✅ | 🔧 | |
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| [relative-url-style](docs/rules/relative-url-style.md) | Enforce consistent relative URL style. | ✅ | 🔧 | 💡 |
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| [require-array-join-separator](docs/rules/require-array-join-separator.md) | Enforce using the separator argument with `Array#join()`. | ✅ | 🔧 | |
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| [require-module-specifiers](docs/rules/require-module-specifiers.md) | Require non-empty specifier list in import and export statements. | ✅ | 🔧 | 💡 |
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| [require-number-to-fixed-digits-argument](docs/rules/require-number-to-fixed-digits-argument.md) | Enforce using the digits argument with `Number#toFixed()`. | ✅ | 🔧 | |
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| [require-post-message-target-origin](docs/rules/require-post-message-target-origin.md) | Enforce using the `targetOrigin` argument with `window.postMessage()`. | | | 💡 |
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| [string-content](docs/rules/string-content.md) | Enforce better string content. | | 🔧 | 💡 |

‎rules/index.js

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export {default as 'prevent-abbreviations'} from './prevent-abbreviations.js';
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export {default as 'relative-url-style'} from './relative-url-style.js';
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export {default as 'require-array-join-separator'} from './require-array-join-separator.js';
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export {default as 'require-module-specifiers'} from './require-module-specifiers.js';
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export {default as 'require-number-to-fixed-digits-argument'} from './require-number-to-fixed-digits-argument.js';
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export {default as 'require-post-message-target-origin'} from './require-post-message-target-origin.js';
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export {default as 'string-content'} from './string-content.js';

‎rules/require-module-specifiers.js

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import {isClosingBraceToken} from '@eslint-community/eslint-utils';
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const MESSAGE_ID_ERROR = 'error';
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const MESSAGE_ID_SUGGESTION_REMOVE_DECLARATION = 'suggestion/remove-declaration';
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const MESSAGE_ID_SUGGESTION_TO_SIDE_EFFECT_IMPORT = 'suggestion/to-side-effect-import';
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const messages = {
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[MESSAGE_ID_ERROR]: '{{type}} statement without specifiers is not allowed.',
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[MESSAGE_ID_SUGGESTION_REMOVE_DECLARATION]: 'Remove this {{type}} statement.',
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[MESSAGE_ID_SUGGESTION_TO_SIDE_EFFECT_IMPORT]: 'Switch to side effect import.',
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};
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const isFromToken = token => token.type === 'Identifier' && token.value === 'from';
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/** @param {import('eslint').Rule.RuleContext} context */
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const create = context => {
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const {sourceCode} = context;
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context.on('ImportDeclaration', importDeclaration => {
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const {specifiers} = importDeclaration;
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if (specifiers.some(node => node.type === 'ImportSpecifier' || node.type === 'ImportNamespaceSpecifier')) {
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return;
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}
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const {source, importKind} = importDeclaration;
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const fromToken = sourceCode.getTokenBefore(source);
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if (!isFromToken(fromToken)) {
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return;
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}
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const closingBraceToken = sourceCode.getTokenBefore(fromToken);
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if (!isClosingBraceToken(closingBraceToken)) {
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return;
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}
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const openingBraceToken = sourceCode.getTokenBefore(closingBraceToken);
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const problem = {
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node: importDeclaration,
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loc: {
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start: sourceCode.getLoc(openingBraceToken).start,
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end: sourceCode.getLoc(closingBraceToken).end,
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},
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messageId: MESSAGE_ID_ERROR,
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data: {
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type: 'import',
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},
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};
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// If there is a `ImportDefaultSpecifier`, it has to be the first.
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const importDefaultSpecifier = specifiers.length === 1 ? specifiers[0] : undefined;
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if (importKind === 'type' && !importDefaultSpecifier) {
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problem.fix = fixer => fixer.remove(importDeclaration);
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return problem;
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}
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if (importDefaultSpecifier) {
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problem.fix = function * (fixer) {
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yield fixer.remove(closingBraceToken);
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yield fixer.remove(openingBraceToken);
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const commaToken = sourceCode.getTokenBefore(openingBraceToken);
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yield fixer.remove(commaToken);
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if (sourceCode.getRange(closingBraceToken)[1] === sourceCode.getRange(fromToken)[0]) {
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yield fixer.insertTextBefore(fromToken, ' ');
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}
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};
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return problem;
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}
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problem.suggest = [
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{
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messageId: MESSAGE_ID_SUGGESTION_REMOVE_DECLARATION,
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fix: fixer => fixer.remove(importDeclaration),
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},
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{
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messageId: MESSAGE_ID_SUGGESTION_TO_SIDE_EFFECT_IMPORT,
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* fix(fixer) {
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yield fixer.remove(openingBraceToken);
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yield fixer.remove(closingBraceToken);
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yield fixer.remove(fromToken);
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},
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},
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];
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return problem;
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});
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context.on('ExportNamedDeclaration', exportDeclaration => {
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const {specifiers, declaration} = exportDeclaration;
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if (declaration || specifiers.length > 0) {
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return;
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}
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const {source, exportKind} = exportDeclaration;
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const fromToken = source ? sourceCode.getTokenBefore(source) : undefined;
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const closingBraceToken = fromToken
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? sourceCode.getTokenBefore(fromToken)
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: sourceCode.getLastToken(exportDeclaration, isClosingBraceToken);
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const openingBraceToken = sourceCode.getTokenBefore(closingBraceToken);
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const problem = {
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node: exportDeclaration,
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loc: {
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start: sourceCode.getLoc(openingBraceToken).start,
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end: sourceCode.getLoc(closingBraceToken).end,
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},
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messageId: MESSAGE_ID_ERROR,
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data: {
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type: 'export',
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},
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};
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if (!source || exportKind === 'type') {
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problem.fix = fixer => fixer.remove(exportDeclaration);
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return problem;
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}
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problem.suggest = [
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{
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messageId: MESSAGE_ID_SUGGESTION_REMOVE_DECLARATION,
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fix: fixer => fixer.remove(exportDeclaration),
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},
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{
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messageId: MESSAGE_ID_SUGGESTION_TO_SIDE_EFFECT_IMPORT,
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* fix(fixer) {
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const exportToken = sourceCode.getFirstToken(exportDeclaration);
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yield fixer.replaceText(exportToken, 'import');
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yield fixer.remove(openingBraceToken);
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yield fixer.remove(closingBraceToken);
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yield fixer.remove(fromToken);
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},
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},
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];
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return problem;
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});
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};
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/** @type {import('eslint').Rule.RuleModule} */
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const config = {
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create,
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meta: {
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type: 'suggestion',
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docs: {
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description: 'Require non-empty specifier list in import and export statements.',
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recommended: true,
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},
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fixable: 'code',
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hasSuggestions: true,
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messages,
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},
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};
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export default config;

‎test/require-module-specifiers.js

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import outdent from 'outdent';
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import {getTester, parsers} from './utils/test.js';
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const {test} = getTester(import.meta);
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const typescriptCode = code => ({
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code,
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languageOptions: {parser: parsers.typescript},
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});
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// `import`
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test.snapshot({
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valid: [
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'import "foo"',
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'import foo from "foo"',
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'import * as foo from "foo"',
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'import {foo} from "foo"',
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'import foo,{bar} from "foo"',
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typescriptCode('import type foo from "foo"'),
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typescriptCode('import * as foo from "foo"'),
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typescriptCode('import type foo,{bar} from "foo"'),
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typescriptCode('import foo,{type bar} from "foo"'),
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],
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invalid: [
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'import {} from "foo";',
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'import{}from"foo";',
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outdent`
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import {
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} from "foo";
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`,
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'import foo, {} from "foo";',
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'import foo,{}from "foo";',
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outdent`
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import foo, {
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} from "foo";
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`,
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'import foo,{}/* comment */from "foo";',
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typescriptCode('import type {} from "foo";'),
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typescriptCode('import type{}from"foo";'),
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typescriptCode('import type foo, {} from "foo";'),
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typescriptCode('import type foo,{}from "foo";'),
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],
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});
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// `export`
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test.snapshot({
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valid: [
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outdent`
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const foo = 1;
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export {foo};
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`,
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'export {foo} from "foo"',
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'export * as foo from "foo"',
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typescriptCode('export type {Foo}'),
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typescriptCode('export type {foo} from "foo"'),
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typescriptCode('export type * as foo from "foo"'),
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'export const foo = 1',
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'export function foo() {}',
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'export class foo {}',
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typescriptCode('export type foo = Foo'),
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'export const {} = foo',
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'export const [] = foo',
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],
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invalid: [
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'export {}',
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typescriptCode('export type{}'),
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typescriptCode('export type {} from "foo";'),
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typescriptCode('declare export type {} from "foo";'),
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'export {} from "foo";',
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'export{}from"foo";',
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outdent`
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export {
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} from "foo";
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`,
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'export {} from "foo" with {type: "json"};',
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],
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});

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