fix(eslint-plugin): [no-unnecessary-type-constraint] correctly fix in cts/mts files

packages/eslint-plugin/src/rules/no-unnecessary-type-constraint.ts

@@ -1,6 +1,7 @@
 import {
   getLanguageVariant,
   getScriptKind,
+  isNewModuleExtension,
 } from '@typescript-eslint/type-utils';
 import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
 import { AST_NODE_TYPES } from '@typescript-eslint/utils';
@@ -64,21 +65,21 @@ export default util.createRule({
         ])
       : new Map([[AST_NODE_TYPES.TSUnknownKeyword, 'unknown']]);
 
-    const inJsx =
-      getLanguageVariant(
-        getScriptKind(
-          context.getFilename(),
-          !!context.parserOptions.ecmaFeatures?.jsx,
-        ),
-      ) === ts.LanguageVariant.JSX;
-
+    const filename = context.getFilename();
+    const scriptKind = getScriptKind(
+      filename,
+      !!context.parserOptions.ecmaFeatures?.jsx,
+    );
+    const inJsx = getLanguageVariant(scriptKind) === ts.LanguageVariant.JSX;
+    const newModuleExtension = isNewModuleExtension(filename);
     const source = context.getSourceCode();
 
     const checkNode = (
       node: TypeParameterWithConstraint,
       inArrowFunction: boolean,
     ): void => {
-      const constraint = unnecessaryConstraints.get(node.constraint.type);
+      const constraint =
+        !newModuleExtension && unnecessaryConstraints.get(node.constraint.type);
       function shouldAddTrailingComma(): boolean {
         if (!inArrowFunction || !inJsx) {
           return false;

packages/eslint-plugin/tests/rules/no-unnecessary-type-constraint.test.ts

@@ -25,6 +25,10 @@ function data<T extends TODO>() {}
     'const data = <T, U>() => {};',
     'const data = <T extends number>() => {};',
     'const data = <T extends number | string>() => {};',
+    {
+      code: 'const data = <T extends any>() => {};',
+      filename: 'file.mts',
+    },
   ],
   invalid: [
     {

packages/type-utils/src/index.ts

@@ -18,4 +18,5 @@ export {
   typescriptVersionIsAtLeast,
   getScriptKind,
   getLanguageVariant,
+  isNewModuleExtension,
 } from '@typescript-eslint/typescript-estree';

packages/typescript-estree/src/create-program/getScriptKind.ts

@@ -1,6 +1,32 @@
 import path from 'path';
 import * as ts from 'typescript';
 
+function isNewModuleExtension(filePath: string): boolean {
+  const extension = path.extname(filePath).toLowerCase();
+  // note - we only respect the user's jsx setting for unknown extensions
+  // this is so that we always match TS's internal script kind logic, preventing
+  // weird errors due to a mismatch.
+  // https://github.com/microsoft/TypeScript/blob/da00ba67ed1182ad334f7c713b8254fba174aeba/src/compiler/utilities.ts#L6948-L6968
+  switch (extension) {
+    case ts.Extension.Js:
+    case ts.Extension.Ts:
+    case ts.Extension.Jsx:
+    case ts.Extension.Tsx:
+    case ts.Extension.Json:
+      return false;
+
+    case ts.Extension.Cjs:
+    case ts.Extension.Mjs:
+    case ts.Extension.Cts:
+    case ts.Extension.Mts:
+      return true;
+
+    default:
+      // unknown extension, we assume this is not a new module extension
+      return false;
+  }
+}
+
 function getScriptKind(filePath: string, jsx: boolean): ts.ScriptKind {
   const extension = path.extname(filePath).toLowerCase();
   // note - we only respect the user's jsx setting for unknown extensions
@@ -47,4 +73,4 @@
   }
 }
 
-export { getScriptKind, getLanguageVariant };
+export { getScriptKind, getLanguageVariant, isNewModuleExtension };