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✨ add node/file-extension-in-import rule
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‎README.md‎

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| Rule ID | Description | |
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|:--------|:------------|:--:|
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| [node/exports-style](./docs/rules/exports-style.md) | enforce either `module.exports` or `exports` | |
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| [node/file-extension-in-import](./docs/rules/file-extension-in-import.md) | enforce the style of file extensions in `import` declarations | ✒️ |
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| [node/prefer-global/buffer](./docs/rules/prefer-global/buffer.md) | enforce either `Buffer` or `require("buffer").Buffer` | |
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| [node/prefer-global/console](./docs/rules/prefer-global/console.md) | enforce either `console` or `require("console")` | |
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| [node/prefer-global/process](./docs/rules/prefer-global/process.md) | enforce either `process` or `require("process")` | |

‎docs/rules/file-extension-in-import.md‎

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# enforce the style of file extensions in `import` declarations (file-extension-in-import)
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We can omit file extensions in `import`/`export` declarations.
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```js
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import foo from "./path/to/a/file" // maybe it's resolved to 'file.js' or 'file.json'
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export * from "./path/to/a/file"
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```
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However, [--experimental-modules](https://medium.com/@nodejs/announcing-a-new-experimental-modules-1be8d2d6c2ff) has declared to drop the file extension omition.
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Also, we can import a variety kind of files with bundlers such as Webpack. In the situation, probably explicit file extensions help us to understand code.
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## Rule Details
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This rule enforces the style of file extensions in `import`/`export` declarations.
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## Options
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This rule has a string option and an object option.
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```json
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{
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"node/file-extension-in-import": [
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"error",
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"always" or "never",
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{
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"tryExtensions": [".js", ".json", ".node"],
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".xxx": "always" or "never",
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}
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]
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}
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```
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- `"always"` (default) requires file extensions in `import`/`export` declarations.
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- `"never"` disallows file extensions in `import`/`export` declarations.
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- `tryExtensions` is the file extensions to resolve import paths. Default is `[".js", ".json", ".node"]`.
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- `.xxx` is the overriding setting for specific file extensions. You can use arbitrary property names which start with `.`.
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### always
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Examples of :-1: **incorrect** code for the `"always"` option:
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```js
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/*eslint node/file-extension-in-import: ["error", "always"]*/
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import foo from "./path/to/a/file"
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```
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Examples of :+1: **correct** code for the `"always"` option:
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```js
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/*eslint node/file-extension-in-import: ["error", "always"]*/
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import eslint from "eslint"
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import foo from "./path/to/a/file.js"
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```
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### never
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Examples of :-1: **incorrect** code for the `"never"` option:
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```js
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/*eslint node/file-extension-in-import: ["error", "never"]*/
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import foo from "./path/to/a/file.js"
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```
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Examples of :+1: **correct** code for the `"never"` option:
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```js
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/*eslint node/file-extension-in-import: ["error", "never"]*/
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import eslint from "eslint"
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import foo from "./path/to/a/file"
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```
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### .xxx
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Examples of :+1: **correct** code for the `["always", { ".js": "never" }]` option:
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```js
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/*eslint node/file-extension-in-import: ["error", "always", { ".js": "never" }]*/
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import eslint from "eslint"
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import script from "./script"
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import styles from "./styles.css"
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import logo from "./logo.png"
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```
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## Shared Settings
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The following options can be set by [shared settings](http://eslint.org/docs/user-guide/configuring.html#adding-shared-settings).
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Several rules have the same option, but we can set this option at once.
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- `tryExtensions`
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```js
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// .eslintrc.js
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module.exports = {
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"settings": {
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"node": {
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"tryExtensions": [".js", ".json", ".node"]
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}
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},
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"rules": {
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"node/file-extension-in-import": "error"
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}
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}
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```

‎lib/index.js‎

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},
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rules: {
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"exports-style": require("./rules/exports-style"),
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"file-extension-in-import": require("./rules/file-extension-in-import"),
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"no-deprecated-api": require("./rules/no-deprecated-api"),
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"no-extraneous-import": require("./rules/no-extraneous-import"),
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"no-extraneous-require": require("./rules/no-extraneous-require"),

‎lib/rules/file-extension-in-import.js‎

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/**
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* @author Toru Nagashima
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* See LICENSE file in root directory for full license.
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*/
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"use strict"
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const path = require("path")
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const fs = require("fs")
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const getImportExportTargets = require("../util/get-import-export-targets")
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const getTryExtensions = require("../util/get-try-extensions")
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/**
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* Get all file extensions of the files which have the same basename.
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* @param {string} filePath The path to the original file to check.
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* @returns {string[]} File extensions.
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*/
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function getExistingExtensions(filePath) {
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const basename = path.basename(filePath, path.extname(filePath))
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try {
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return fs
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.readdirSync(path.dirname(filePath))
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.filter(
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filename =>
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path.basename(filename, path.extname(filename)) === basename
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)
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.map(filename => path.extname(filename))
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} catch (_error) {
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return []
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}
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}
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module.exports = {
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meta: {
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docs: {
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description:
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"enforce the style of file extensions in `import` declarations",
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category: "Stylistic Issues",
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recommended: false,
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url:
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"https://github.com/mysticatea/eslint-plugin-node/blob/v8.0.1/docs/rules/file-extension-in-import.md",
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},
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fixable: "code",
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messages: {
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requireExt: "require file extension '{{ext}}'.",
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forbidExt: "forbid file extension '{{ext}}'.",
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},
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schema: [
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{
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enum: ["always", "never"],
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},
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{
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type: "object",
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properties: {
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tryExtensions: getTryExtensions.schema,
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},
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additionalProperties: {
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enum: ["always", "never"],
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},
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},
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],
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type: "suggestion",
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},
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create(context) {
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if (context.getFilename().startsWith("<")) {
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return {}
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}
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const defaultStyle = context.options[0] || "always"
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const overrideStyle = context.options[1] || {}
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function verify({ filePath, name, node }) {
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// Ignore if it's not resolved to a file or it's a bare module.
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if (!filePath || !/[/\\]/u.test(name)) {
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return
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}
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// Get extension.
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const originalExt = path.extname(name)
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const resolvedExt = path.extname(filePath)
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const existingExts = getExistingExtensions(filePath)
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if (!resolvedExt && existingExts.length !== 1) {
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// Ignore if the file extension could not be determined one.
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return
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}
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const ext = resolvedExt || existingExts[0]
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const style = overrideStyle[ext] || defaultStyle
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// Verify.
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if (style === "always" && ext !== originalExt) {
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context.report({
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node,
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messageId: "requireExt",
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data: { ext },
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fix(fixer) {
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if (existingExts.length !== 1) {
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return null
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}
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const index = node.range[1] - 1
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return fixer.insertTextBeforeRange([index, index], ext)
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},
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})
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} else if (style === "never" && ext === originalExt) {
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context.report({
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node,
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messageId: "forbidExt",
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data: { ext },
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fix(fixer) {
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if (existingExts.length !== 1) {
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return null
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}
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const index = name.lastIndexOf(ext)
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const start = node.range[0] + 1 + index
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const end = start + ext.length
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return fixer.removeRange([start, end])
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},
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})
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}
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}
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return {
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"Program:exit"(node) {
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const opts = { optionIndex: 1 }
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getImportExportTargets(context, node, opts).forEach(verify)
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},
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}
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},
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}

‎lib/rules/no-hide-core-modules.js‎

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const targets = []
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.concat(
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getRequireTargets(context, true),
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getImportExportTargets(context, node, true)
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getImportExportTargets(context, node, {
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includeCore: true,
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})
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)
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.filter(t => CORE_MODULES.has(t.moduleName))
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‎lib/util/get-import-export-targets.js‎

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*
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* @param {RuleContext} context - The rule context.
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* @param {ASTNode} programNode - The node of Program.
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* @param {boolean} includeCore - The flag to include core modules.
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* @param {Object} [options] - The flag to include core modules.
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* @param {boolean} [options.includeCore] - The flag to include core modules.
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* @param {number} [options.optionIndex] - The index of rule options.
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* @returns {ImportTarget[]} A list of found target's information.
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*/
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module.exports = function getImportExportTargets(
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context,
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programNode,
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includeCore
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{ includeCore = false, optionIndex = 0 } = {}
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) {
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const retv = []
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const basedir = path.dirname(path.resolve(context.getFilename()))
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const paths = getResolvePaths(context)
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const extensions = getTryExtensions(context)
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const paths = getResolvePaths(context, optionIndex)
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const extensions = getTryExtensions(context, optionIndex)
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const options = { basedir, paths, extensions }
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for (const statement of programNode.body) {

‎lib/util/get-resolve-paths.js‎

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* @param {RuleContext} context - The rule context.
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* @returns {string[]} A list of extensions.
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*/
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module.exports = function getResolvePaths(context) {
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module.exports = function getResolvePaths(context, optionIndex = 0) {
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return (
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get(context.options && context.options[0]) ||
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get(context.options && context.options[optionIndex]) ||
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get(context.settings && context.settings.node) ||
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DEFAULT_VALUE
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)

‎lib/util/get-try-extensions.js‎

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* @param {RuleContext} context - The rule context.
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* @returns {string[]} A list of extensions.
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*/
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module.exports = function getTryExtensions(context) {
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module.exports = function getTryExtensions(context, optionIndex = 0) {
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return (
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get(context.options && context.options[0]) ||
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get(context.options && context.options[optionIndex]) ||
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get(context.settings && context.settings.node) ||
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DEFAULT_VALUE
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)

‎tests/fixtures/file-extension-in-import/a.js‎

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‎tests/fixtures/file-extension-in-import/b.json‎

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