fix(eslint-plugin): [no-unnecessary-type-constraint] correctly fix in cts/mts files (typescript-eslint#6795)

WoodyWoodsta · bradzacher · web-flow · commit 14047963d79e · 2023-07-17T11:26:24.000+09:30
Co-authored-by: Brad Zacher &lt;brad.zacher@gmail.com&gt;
diff --git a/packages/eslint-plugin/src/rules/no-unnecessary-type-constraint.ts b/packages/eslint-plugin/src/rules/no-unnecessary-type-constraint.ts
@@ -1,5 +1,7 @@
 import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
 import { AST_NODE_TYPES } from '@typescript-eslint/utils';
+import { extname } from 'path';
+import * as ts from 'typescript';
 
 import * as util from '../util';
 
@@ -38,7 +40,24 @@ export default util.createRule({
       [AST_NODE_TYPES.TSUnknownKeyword, 'unknown'],
     ]);
 
-    const inJsx = context.getFilename().toLowerCase().endsWith('tsx');
+    function checkRequiresGenericDeclarationDisambiguation(
+      filename: string,
+    ): boolean {
+      const pathExt = extname(filename).toLocaleLowerCase();
+      switch (pathExt) {
+        case ts.Extension.Cts:
+        case ts.Extension.Mts:
+        case ts.Extension.Tsx:
+          return true;
+
+        default:
+          return false;
+      }
+    }
+
+    const requiresGenericDeclarationDisambiguation =
+      checkRequiresGenericDeclarationDisambiguation(context.getFilename());
+
     const source = context.getSourceCode();
 
     const checkNode = (
@@ -47,7 +66,7 @@ export default util.createRule({
     ): void => {
       const constraint = unnecessaryConstraints.get(node.constraint.type);
       function shouldAddTrailingComma(): boolean {
-        if (!inArrowFunction || !inJsx) {
+        if (!inArrowFunction || !requiresGenericDeclarationDisambiguation) {
           return false;
         }
         // Only <T>() => {} would need trailing comma
diff --git a/packages/eslint-plugin/tests/rules/no-unnecessary-type-constraint.test.ts b/packages/eslint-plugin/tests/rules/no-unnecessary-type-constraint.test.ts
@@ -128,6 +128,46 @@ function data<T extends TODO>() {}
         },
       },
     },
+    {
+      code: 'const data = <T extends any>() => {};',
+      errors: [
+        {
+          data: { constraint: 'any', name: 'T' },
+          messageId: 'unnecessaryConstraint',
+          endColumn: 28,
+          column: 15,
+          line: 1,
+          suggestions: [
+            {
+              messageId: 'removeUnnecessaryConstraint',
+              data: { constraint: 'any' },
+              output: `const data = <T,>() => {};`,
+            },
+          ],
+        },
+      ],
+      filename: 'file.mts',
+    },
+    {
+      code: 'const data = <T extends any>() => {};',
+      errors: [
+        {
+          data: { constraint: 'any', name: 'T' },
+          messageId: 'unnecessaryConstraint',
+          endColumn: 28,
+          column: 15,
+          line: 1,
+          suggestions: [
+            {
+              messageId: 'removeUnnecessaryConstraint',
+              data: { constraint: 'any' },
+              output: `const data = <T,>() => {};`,
+            },
+          ],
+        },
+      ],
+      filename: 'file.cts',
+    },
     {
       code: noFormat`const data = <T extends any,>() => {};`,
       errors: [
