Fix no-missing-import for typescript

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

@@ -6,15 +6,11 @@
 
 const path = require("path")
 const fs = require("fs")
+const mapTypescriptExtension = require("../util/map-typescript-extension.js")
 const visitImport = require("../util/visit-import")
 const packageNamePattern = /^(?:@[^/\\]+[/\\])?[^/\\]+$/u
 const corePackageOverridePattern =
     /^(?:assert|async_hooks|buffer|child_process|cluster|console|constants|crypto|dgram|dns|domain|events|fs|http|http2|https|inspector|module|net|os|path|perf_hooks|process|punycode|querystring|readline|repl|stream|string_decoder|sys|timers|tls|trace_events|tty|url|util|v8|vm|worker_threads|zlib)[/\\]$/u
-const typescriptFileExtensionsMapping = {
-    ".ts": ".js",
-    ".cts": ".cjs",
-    ".mts": ".mjs",
-}
 
 /**
  * Get all file extensions of the files which have the same basename.
@@ -36,27 +32,6 @@ function getExistingExtensions(filePath) {
     }
 }
 
-/**
- * Get the file extension that should be added in an import statement,
- * based on the given file extension of the referenced file.
- *
- * 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 {string} referencedFileExt The original file extension of the referenced file.
- * @param {string} referencingFileExt The original file extension of the file the contains the import statement.
- * @returns {string} The file extension to append to the import statement.
- */
-function getFileExtensionToAdd(referencedFileExt, referencingFileExt) {
-    if (
-        referencingFileExt in typescriptFileExtensionsMapping &&
-        referencedFileExt in typescriptFileExtensionsMapping
-    ) {
-        return typescriptFileExtensionsMapping[referencedFileExt]
-    }
-
-    return referencedFileExt
-}
-
 module.exports = {
     meta: {
         docs: {
@@ -104,19 +79,16 @@ module.exports = {
 
             // Get extension.
             const originalExt = path.extname(name)
-            const resolvedExt = path.extname(filePath)
             const existingExts = getExistingExtensions(filePath)
-            const ext = resolvedExt || existingExts.join(" or ")
+            const ext = path.extname(filePath) || existingExts.join(" or ")
             const style = overrideStyle[ext] || defaultStyle
 
             // Verify.
             if (style === "always" && ext !== originalExt) {
-                const referencingFileExt = path.extname(
-                    context.getPhysicalFilename()
-                )
-                const fileExtensionToAdd = getFileExtensionToAdd(
-                    ext,
-                    referencingFileExt
+                const fileExtensionToAdd = mapTypescriptExtension(
+                    context,
+                    filePath,
+                    ext
                 )
                 context.report({
                     node,

lib/util/check-existence.js

@@ -4,8 +4,11 @@
  */
 "use strict"
 
+const path = require("path")
 const exists = require("./exists")
 const getAllowModules = require("./get-allow-modules")
+const isTypescript = require("./is-typescript.js")
+const mapTypescriptExtension = require("../util/map-typescript-extension.js")
 
 /**
  * Checks whether or not each requirement target exists.
@@ -17,16 +20,28 @@ const getAllowModules = require("./get-allow-modules")
  * @param {ImportTarget[]} targets - A list of target information to check.
  * @returns {void}
  */
-module.exports = function checkForExistence(context, targets) {
+module.exports = function checkExistence(context, targets) {
     const allowed = new Set(getAllowModules(context))
 
     for (const target of targets) {
         const missingModule =
             target.moduleName != null &&
             !allowed.has(target.moduleName) &&
             target.filePath == null
-        const missingFile =
-            target.moduleName == null && !exists(target.filePath)
+
+        let missingFile = target.moduleName == null && !exists(target.filePath)
+        if (missingFile && isTypescript(context)) {
+            const parsed = path.parse(target.filePath)
+            const reversedExt = mapTypescriptExtension(
+                context,
+                target.filePath,
+                parsed.ext,
+                true
+            )
+            const reversedPath =
+                path.resolve(parsed.dir, parsed.name) + reversedExt
+            missingFile = target.moduleName == null && !exists(reversedPath)
+        }
 
         if (missingModule || missingFile) {
             context.report({

lib/util/is-typescript.js

@@ -0,0 +1,16 @@
+"use strict"
+
+const path = require("path")
+
+const typescriptExtensions = [".ts", ".cts", ".mts"]
+
+/**
+ * Determine if the context source file is typescript.
+ *
+ * @param {RuleContext} context - A context
+ * @returns {boolean}
+ */
+module.exports = function isTypescript(context) {
+    const sourceFileExt = path.extname(context.getPhysicalFilename())
+    return typescriptExtensions.includes(sourceFileExt)
+}

lib/util/map-typescript-extension.js

@@ -0,0 +1,49 @@
+"use strict"
+
+const path = require("path")
+const isTypescript = require("../util/is-typescript")
+
+const mapping = {
+    ".ts": ".js",
+    ".cts": ".cjs",
+    ".mts": ".mjs",
+}
+
+const reverseMapping = {
+    ".js": ".ts",
+    ".cjs": ".cts",
+    ".mjs": ".mts",
+}
+
+/**
+ * Maps the typescript file extension that should be added in an import statement,
+ * based on the given file extension of the referenced file OR fallsback to the original given extension.
+ *
+ * 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 {string} filePath The filePath of the import
+ * @param {string} fallbackExtension The non-typescript fallback
+ * @param {boolean} reverse Execute a reverse path mapping
+ * @returns {string} The file extension to append to the import statement.
+ */
+module.exports = function mapTypescriptExtension(
+    context,
+    filePath,
+    fallbackExtension,
+    reverse = false
+) {
+    const ext = path.extname(filePath)
+    if (reverse) {
+        if (isTypescript(context) && ext in reverseMapping) {
+            return reverseMapping[ext]
+        }
+    } else {
+        if (isTypescript(context) && ext in mapping) {
+            return mapping[ext]
+        }
+    }
+
+    return fallbackExtension
+}

tests/lib/rules/no-missing-import.js

@@ -58,6 +58,14 @@ ruleTester.run("no-missing-import", rule, {
             filename: fixture("test.js"),
             code: "import a from './a.js';",
         },
+        {
+            filename: fixture("test.ts"),
+            code: "import a from './a.js';",
+        },
+        {
+            filename: fixture("test.ts"),
+            code: "import a from './d.ts';",
+        },
         {
             filename: fixture("test.js"),
             code: "import aConfig from './a.config.js';",
@@ -166,6 +174,11 @@ ruleTester.run("no-missing-import", rule, {
             code: "import c from './c';",
             errors: ['"./c" is not found.'],
         },
+        {
+            filename: fixture("test.ts"),
+            code: "import d from './d';",
+            errors: ['"./d" is not found.'],
+        },
         {
             filename: fixture("test.js"),
             code: "import d from './d';",