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Add no-barrel-files rule (#3570)
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‎docs/rules/no-barrel-files.md‎

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# no-barrel-files
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📝 Disallow barrel files.
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🚫 This rule is _disabled_ in the following [configs](https://github.com/sindresorhus/eslint-plugin-unicorn#recommended-config): ✅ `recommended`, ☑️ `unopinionated`.
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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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A barrel file only imports and re-exports bindings, including type-only bindings, from other modules. Barrel files make it less clear where a dependency comes from and can cause consumers to load more modules than they need.
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This rule treats any file whose top-level body consists only of imports and re-exports as a barrel, including a file that re-exports from only one module. It is intentionally syntax-only: it does not resolve modules or try to distinguish package entry points from internal barrel files. Disable it in intentional entry points.
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At least one binding must be re-exported; files containing only empty exports are ignored. The rule recognizes ECMAScript module syntax, including TypeScript's type-only extensions.
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Side-effect-only imports, including `import 'foo'` and `import {} from 'foo'`, are not part of a barrel file, so a file that combines one with re-exports is ignored.
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Fix violations by removing the barrel file and importing directly from its source modules, for example, replace `import {foo} from './index.js'` with `import {foo} from './foo.js'`. Disable this rule for intentional package entry points.
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## Examples
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Examples of **incorrect** code for this rule:
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```js
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export {foo} from './foo.js';
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```
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```js
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import {foo} from './foo.js';
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export {foo};
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```
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```js
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export * from './foo.js';
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export * from './bar.js';
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```
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Examples of **correct** code for this rule:
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```js
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export const foo = 1;
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```
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```js
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import {foo} from './foo.js';
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export const bar = foo;
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```
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```js
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export {foo} from './foo.js';
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export const bar = 1;
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```

‎eslint.dogfooding.config.js‎

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'unicorn/prefer-simplified-conditions': 'off',
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// Many existing internal utilities intentionally export declarations separately.
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'unicorn/default-export-style': 'off',
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// The plugin intentionally keeps a few internal barrel files for shared utilities and rule exports.
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'unicorn/no-barrel-files': 'off',
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// TODO: Enable when targeting Node.js 26.
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'unicorn/prefer-iterator-concat': 'off',
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'unicorn/prefer-temporal': 'off',

‎readme.md‎

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| [no-async-promise-finally](docs/rules/no-async-promise-finally.md) | Disallow async functions as `Promise#finally()` callbacks. | ✅ ☑️ | | | |
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| [no-await-expression-member](docs/rules/no-await-expression-member.md) | Disallow member access from await expression. | ✅ | 🔧 | | |
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| [no-await-in-promise-methods](docs/rules/no-await-in-promise-methods.md) | Disallow using `await` in `Promise` method parameters. | ✅ ☑️ | | 💡 | |
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| [no-barrel-files](docs/rules/no-barrel-files.md) | Disallow barrel files. | | | | |
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| [no-blob-to-file](docs/rules/no-blob-to-file.md) | Disallow unnecessary `Blob` to `File` conversion. | ✅ ☑️ | | 💡 | |
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| [no-boolean-sort-comparator](docs/rules/no-boolean-sort-comparator.md) | Disallow boolean-returning sort comparators. | ✅ ☑️ | | 💡 | |
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| [no-break-in-nested-loop](docs/rules/no-break-in-nested-loop.md) | Disallow `break` and `continue` in nested loops and switches inside loops. | ✅ | | | |

‎rules/index.js‎

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export {default as 'no-async-promise-finally'} from './no-async-promise-finally.js';
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export {default as 'no-await-expression-member'} from './no-await-expression-member.js';
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export {default as 'no-await-in-promise-methods'} from './no-await-in-promise-methods.js';
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export {default as 'no-barrel-files'} from './no-barrel-files.js';
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export {default as 'no-blob-to-file'} from './no-blob-to-file.js';
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export {default as 'no-boolean-sort-comparator'} from './no-boolean-sort-comparator.js';
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export {default as 'no-break-in-nested-loop'} from './no-break-in-nested-loop.js';

‎rules/no-barrel-files.js‎

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/** @import * as ESLint from 'eslint'; */
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import {unwrapTypeScriptExpression} from './utils/index.js';
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const MESSAGE_ID = 'no-barrel-files';
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const messages = {
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[MESSAGE_ID]: 'Barrel files are not allowed.',
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};
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const getImportedBindingNames = program => {
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const importedBindingNames = new Set();
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for (const node of program.body) {
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if (node.type !== 'ImportDeclaration') {
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continue;
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}
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for (const specifier of node.specifiers) {
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importedBindingNames.add(specifier.local.name);
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}
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}
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return importedBindingNames;
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};
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const isBarrelFile = program => {
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const importedBindingNames = getImportedBindingNames(program);
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let hasReExport = false;
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for (const node of program.body) {
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if (node.type === 'ImportDeclaration') {
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if (node.specifiers.length === 0) {
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return false;
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}
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continue;
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}
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if (node.type === 'ExportAllDeclaration') {
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hasReExport = true;
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continue;
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}
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if (node.type === 'ExportNamedDeclaration') {
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if (
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node.declaration
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|| (!node.source && node.specifiers.some(specifier => !importedBindingNames.has(specifier.local.name)))
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) {
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return false;
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}
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hasReExport ||= node.specifiers.length > 0;
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continue;
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}
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if (node.type === 'ExportDefaultDeclaration') {
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let declaration = unwrapTypeScriptExpression(node.declaration);
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while (declaration.type === 'TSInstantiationExpression') {
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declaration = unwrapTypeScriptExpression(declaration.expression);
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}
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if (declaration.type === 'Identifier' && importedBindingNames.has(declaration.name)) {
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hasReExport = true;
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continue;
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}
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}
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return false;
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}
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return hasReExport;
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};
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/** @param {ESLint.Rule.RuleContext} context */
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const create = context => {
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context.on('Program', node => {
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if (!isBarrelFile(node)) {
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return;
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}
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return {
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node,
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messageId: MESSAGE_ID,
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};
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});
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};
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/** @type {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: 'Disallow barrel files.',
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recommended: false,
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},
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schema: [],
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messages,
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languages: [
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'js/js',
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],
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},
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};
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export default config;

‎test/no-barrel-files.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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test.snapshot({
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valid: [
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'import "foo";',
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'import {} from "foo";',
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'import {} from "foo"; export {bar} from "bar";',
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'import {foo} from "foo"; export const bar = foo;',
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'export {};',
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'export {} from "foo";',
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'const foo = 1; export {foo};',
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'export {foo} from "foo"; const bar = 1;',
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'export const foo = 1;',
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'export default foo;',
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'export default function foo() {}',
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'import "foo"; export {bar} from "bar";',
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outdent`
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import {foo} from './foo.js';
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const bar = foo;
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export {bar};
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`,
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],
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invalid: [
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'export {foo} from "foo";',
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'export {foo as bar} from "foo";',
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'export {default} from "foo";',
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'export * from "foo";',
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'export * as namespace from "foo";',
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'export {}; export {foo} from "foo";',
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'import {foo} from "foo"; export {foo};',
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'import {foo as bar} from "foo"; export {bar};',
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'import foo from "foo"; export default foo;',
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'export default foo; import foo from "foo";',
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'import * as namespace from "foo"; export {namespace as default};',
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'export {foo}; import {foo} from "foo";',
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outdent`
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import {foo} from './foo.js';
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export {foo};
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export {bar} from './bar.js';
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`,
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outdent`
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// This is still a barrel file.
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export {};
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export {foo} from './foo.js';
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export {bar} from './bar.js';
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`,
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{
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code: 'export type {Foo} from "foo";',
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languageOptions: {parser: parsers.typescript},
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},
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{
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code: 'export type * from "foo";',
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languageOptions: {parser: parsers.typescript},
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},
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{
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code: 'export type * as Namespace from "foo";',
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languageOptions: {parser: parsers.typescript},
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},
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{
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code: 'import foo from "foo"; export default foo as Foo;',
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languageOptions: {parser: parsers.typescript},
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},
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{
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code: 'import foo from "foo"; export default foo satisfies Foo;',
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languageOptions: {parser: parsers.typescript},
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},
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{
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code: 'import foo from "foo"; export default foo!;',
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languageOptions: {parser: parsers.typescript},
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},
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{
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code: 'import foo from "foo"; export default foo<string>;',
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languageOptions: {parser: parsers.typescript},
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},
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{
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code: 'import foo from "foo"; export default <Foo>foo;',
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languageOptions: {parser: parsers.typescript},
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},
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{
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code: outdent`
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import type {Foo} from './foo.js';
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export type {Foo};
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`,
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languageOptions: {parser: parsers.typescript},
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},
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],
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});

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