feat: add the ability to configure typescript to javascript file extension conversion

docs/rules/no-missing-import.md

@@ -69,13 +69,30 @@ If a path is relative, it will be resolved from CWD.
 
 Default is `[]`
 
+#### typescriptExtensionMap
+
+Adds the ability to change the extension mapping when converting between typescript and javascript
+
+Default is:
+
+```json
+[
+    [ "", ".js" ],
+    [ ".ts", ".js" ],
+    [ ".cts", ".cjs" ],
+    [ ".mts", ".mjs" ],
+    [ ".tsx", ".jsx" ],
+]
+```
+
 ### Shared Settings
 
 The following options can be set by [shared settings](http://eslint.org/docs/user-guide/configuring.html#adding-shared-settings).
 Several rules have the same option, but we can set this option at once.
 
 - `allowModules`
 - `resolvePaths`
+- `typescriptExtensionMap`
 
 ```js
 // .eslintrc.js
@@ -84,6 +101,13 @@ module.exports = {
         "node": {
             "allowModules": ["electron"],
             "resolvePaths": [__dirname],
+            "typescriptExtensionMap": [
+                [ "", ".js" ],
+                [ ".ts", ".js" ],
+                [ ".cts", ".cjs" ],
+                [ ".mts", ".mjs" ],
+                [ ".tsx", ".js" ],
+            ]
         }
     },
     "rules": {

docs/rules/no-missing-require.md

@@ -82,6 +82,22 @@ When an import path does not exist, this rule checks whether or not any of `path
 
 Default is `[".js", ".json", ".node"]`.
 
+#### typescriptExtensionMap
+
+Adds the ability to change the extension mapping when converting between typescript and javascript
+
+Default is:
+
+```json
+[
+    [ "", ".js" ],
+    [ ".ts", ".js" ],
+    [ ".cts", ".cjs" ],
+    [ ".mts", ".mjs" ],
+    [ ".tsx", ".jsx" ],
+]
+```
+
 ### Shared Settings
 
 The following options can be set by [shared settings](http://eslint.org/docs/user-guide/configuring.html#adding-shared-settings).
@@ -90,6 +106,7 @@ Several rules have the same option, but we can set this option at once.
 - `allowModules`
 - `resolvePaths`
 - `tryExtensions`
+- `typescriptExtensionMap`
 
 ```js
 // .eslintrc.js
@@ -98,7 +115,14 @@ module.exports = {
         "node": {
             "allowModules": ["electron"],
             "resolvePaths": [__dirname],
-            "tryExtensions": [".js", ".json", ".node"]
+            "tryExtensions": [".js", ".json", ".node"],
+            "typescriptExtensionMap": [
+                [ "", ".js" ],
+                [ ".ts", ".js" ],
+                [ ".cts", ".cjs" ],
+                [ ".mts", ".mjs" ],
+                [ ".tsx", ".js" ],
+            ]
         }
     },
     "rules": {

lib/rules/no-missing-import.js

@@ -7,6 +7,7 @@
 const { checkExistence, messages } = require("../util/check-existence")
 const getAllowModules = require("../util/get-allow-modules")
 const getResolvePaths = require("../util/get-resolve-paths")
+const getTypescriptExtensionMap = require("../util/get-typescript-extension-map")
 const visitImport = require("../util/visit-import")
 
 module.exports = {
@@ -26,6 +27,7 @@ module.exports = {
                 properties: {
                     allowModules: getAllowModules.schema,
                     resolvePaths: getResolvePaths.schema,
+                    typescriptExtensionMap: getTypescriptExtensionMap.schema,
                 },
                 additionalProperties: false,
             },

lib/rules/no-missing-require.js

@@ -8,6 +8,7 @@ const { checkExistence, messages } = require("../util/check-existence")
 const getAllowModules = require("../util/get-allow-modules")
 const getResolvePaths = require("../util/get-resolve-paths")
 const getTryExtensions = require("../util/get-try-extensions")
+const getTypescriptExtensionMap = require("../util/get-typescript-extension-map")
 const visitRequire = require("../util/visit-require")
 
 module.exports = {
@@ -28,6 +29,7 @@ module.exports = {
                     allowModules: getAllowModules.schema,
                     tryExtensions: getTryExtensions.schema,
                     resolvePaths: getResolvePaths.schema,
+                    typescriptExtensionMap: getTypescriptExtensionMap.schema,
                 },
                 additionalProperties: false,
             },

lib/util/check-existence.js

@@ -32,17 +32,21 @@ exports.checkExistence = function checkExistence(context, targets) {
         let missingFile = target.moduleName == null && !exists(target.filePath)
         if (missingFile && isTypescript(context)) {
             const parsed = path.parse(target.filePath)
-            const reversedExt = mapTypescriptExtension(
+            const reversedExts = mapTypescriptExtension(
                 context,
                 target.filePath,
                 parsed.ext,
                 true
             )
-            const reversedPath =
-                path.resolve(parsed.dir, parsed.name) + reversedExt
-            missingFile = target.moduleName == null && !exists(reversedPath)
+            const reversedPaths = reversedExts.map(
+                reversedExt =>
+                    path.resolve(parsed.dir, parsed.name) + reversedExt
+            )
+            missingFile = reversedPaths.every(
+                reversedPath =>
+                    target.moduleName == null && !exists(reversedPath)
+            )
         }
-
         if (missingModule || missingFile) {
             context.report({
                 node: target.node,

lib/util/get-typescript-extension-map.js

@@ -0,0 +1,81 @@
+"use strict"
+
+const DEFAULT_MAPPING = normalise([
+    ["", ".js"],
+    [".ts", ".js"],
+    [".cts", ".cjs"],
+    [".mts", ".mjs"],
+    [".tsx", ".jsx"],
+])
+
+/**
+ * @typedef {Object} ExtensionMap
+ * @property {Record<string, string>} forward Convert from typescript to javascript
+ * @property {Record<string, string[]>} backward Convert from javascript to typescript
+ */
+
+function normalise(typescriptExtensionMap) {
+    const forward = {}
+    const backward = {}
+    for (const [typescript, javascript] of typescriptExtensionMap) {
+        forward[typescript] = javascript
+        if (!typescript) {
+            continue
+        }
+        backward[javascript] ??= []
+        backward[javascript].push(typescript)
+    }
+    return { forward, backward }
+}
+
+/**
+ * Gets `typescriptExtensionMap` property from a given option object.
+ *
+ * @param {object|undefined} option - An option object to get.
+ * @returns {ExtensionMap} The `typescriptExtensionMap` value, or `null`.
+ */
+function get(option) {
+    if (
+        option &&
+        option.typescriptExtensionMap &&
+        Array.isArray(option.typescriptExtensionMap)
+    ) {
+        return normalise(option.typescriptExtensionMap)
+    }
+
+    return null
+}
+
+/**
+ * Gets "typescriptExtensionMap" setting.
+ *
+ * 1. This checks `options` property, then returns it if exists.
+ * 2. This checks `settings.n` | `settings.node` property, then returns it if exists.
+ * 3. This returns `DEFAULT_MAPPING`.
+ *
+ * @param {import('eslint').Rule.RuleContext} context - The rule context.
+ * @returns {string[]} A list of extensions.
+ */
+module.exports = function getTypescriptExtensionMap(context) {
+    return (
+        get(context.options && context.options[0]) ||
+        get(
+            context.settings && (context.settings.n || context.settings.node)
+        ) ||
+        // TODO: Detect tsconfig.json here
+        DEFAULT_MAPPING
+    )
+}
+
+module.exports.schema = {
+    type: "array",
+    items: {
+        type: "array",
+        prefixItems: [
+            { type: "string", pattern: "^(?:|\\.\\w+)$" },
+            { type: "string", pattern: "^\\.\\w+$" },
+        ],
+        additionalItems: false,
+    },
+    uniqueItems: true,
+}

lib/util/map-typescript-extension.js

@@ -1,22 +1,8 @@
 "use strict"
 
 const path = require("path")
-const isTypescript = require("../util/is-typescript")
-
-const mapping = {
-    "": ".js", // default empty extension will map to js
-    ".ts": ".js",
-    ".cts": ".cjs",
-    ".mts": ".mjs",
-    ".tsx": ".jsx",
-}
-
-const reverseMapping = {
-    ".js": ".ts",
-    ".cjs": ".cts",
-    ".mjs": ".mts",
-    ".jsx": ".tsx",
-}
+const isTypescript = require("./is-typescript")
+const getTypescriptExtensionMap = require("./get-typescript-extension-map")
 
 /**
  * Maps the typescript file extension that should be added in an import statement,
@@ -25,7 +11,7 @@ const reverseMapping = {
  * For example, in typescript, when referencing another typescript from a typescript file,
  * a .js extension should be used instead of the original .ts extension of the referenced file.
  *
- * @param {RuleContext} context
+ * @param {import('eslint').Rule.RuleContext} context
  * @param {string} filePath The filePath of the import
  * @param {string} fallbackExtension The non-typescript fallback
  * @param {boolean} reverse Execute a reverse path mapping
@@ -37,14 +23,16 @@ module.exports = function mapTypescriptExtension(
     fallbackExtension,
     reverse = false
 ) {
+    const { forward, backward } = getTypescriptExtensionMap(context)
     const ext = path.extname(filePath)
     if (reverse) {
-        if (isTypescript(context) && ext in reverseMapping) {
-            return reverseMapping[ext]
+        if (isTypescript(context) && ext in backward) {
+            return backward[ext]
         }
+        return [fallbackExtension]
     } else {
-        if (isTypescript(context) && ext in mapping) {
-            return mapping[ext]
+        if (isTypescript(context) && ext in forward) {
+            return forward[ext]
         }
     }
 

package.json

@@ -26,6 +26,7 @@
     "devDependencies": {
         "@eslint/eslintrc": "^2.0.3",
         "@eslint/js": "^8.43.0",
+        "@types/eslint": "^8.44.2",
         "@typescript-eslint/parser": "^5.60.0",
         "codecov": "^3.8.2",
         "esbuild": "^0.18.7",

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

@@ -21,6 +21,14 @@ if (!DynamicImportSupported) {
     )
 }
 
+const tsReactExtensionMap = [
+    ["", ".js"],
+    [".ts", ".js"],
+    [".cts", ".cjs"],
+    [".mts", ".mjs"],
+    [".tsx", ".js"],
+]
+
 function fixture(filename) {
     return path.resolve(
         __dirname,
@@ -146,6 +154,32 @@ new RuleTester({
             code: "import './c'",
             options: ["never", { ".json": "always" }],
         },
+
+        // typescriptExtensionMap
+        {
+            filename: fixture("test.tsx"),
+            code: "require('./d.js');",
+            env: { node: true },
+            settings: { node: { typescriptExtensionMap: tsReactExtensionMap } },
+        },
+        {
+            filename: fixture("test.tsx"),
+            code: "require('./e.js');",
+            env: { node: true },
+            settings: { node: { typescriptExtensionMap: tsReactExtensionMap } },
+        },
+        {
+            filename: fixture("test.ts"),
+            code: "require('./d.js');",
+            env: { node: true },
+            settings: { node: { typescriptExtensionMap: tsReactExtensionMap } },
+        },
+        {
+            filename: fixture("test.ts"),
+            code: "require('./e.js');",
+            env: { node: true },
+            settings: { node: { typescriptExtensionMap: tsReactExtensionMap } },
+        },
     ],
     invalid: [
         {