From cc7c47455ec897ae3d8be2bb3411fc6c8535e39c Mon Sep 17 00:00:00 2001
From: fisker Cheung <lionkay@gmail.com>
Date: Tue, 20 Jan 2026 21:59:28 +0800
Subject: [PATCH] Forbid type parameters on `constructor` (#18686)

---
 src/language-js/parse/babel.js                |  2 --
 .../tuple/__snapshots__/format.test.js.snap   | 20 +++++++++++++++++++
 .../errors/typescript/tuple/format.test.js    | 17 ++++++++++++++++
 3 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/src/language-js/parse/babel.js b/src/language-js/parse/babel.js
index e0cb0d76e..018708292 100644
--- a/src/language-js/parse/babel.js
+++ b/src/language-js/parse/babel.js
@@ -192,8 +192,6 @@ const allowedReasonCodes = new Set([
   "StrictFunction",
   "ForInOfLoopInitializer",
 
-  "ConstructorHasTypeParameters",
-
   "DecoratorExportClass",
   "ParamDupe",
   "InvalidDecimal",
diff --git a/tests/format/misc/errors/typescript/tuple/__snapshots__/format.test.js.snap b/tests/format/misc/errors/typescript/tuple/__snapshots__/format.test.js.snap
index 778208ad6..6cc635c1f 100644
--- a/tests/format/misc/errors/typescript/tuple/__snapshots__/format.test.js.snap
+++ b/tests/format/misc/errors/typescript/tuple/__snapshots__/format.test.js.snap
@@ -14,6 +14,13 @@ exports[`snippet: #0 [babel-ts] format 2`] = `
 Cause: A required element cannot follow an optional element. (1:17)"
 `;
 
+exports[`snippet: #0 [babel-ts] format 3`] = `
+"Type parameters cannot appear on a constructor declaration. (1:24)
+> 1 | class A { 'constructor'<a>() {} }
+    |                        ^
+Cause: Type parameters cannot appear on a constructor declaration. (1:23)"
+`;
+
 exports[`snippet: #0 [oxc-ts] format 1`] = `
 "Expected \`,\` or \`]\` but found \`:\` (1:14)
 > 1 | type T = [x.y: A];
@@ -40,12 +47,25 @@ exports[`snippet: #1 [babel-ts] format 1`] = `
 Cause: Tuple members must be labeled with a simple identifier. (1:10)"
 `;
 
+exports[`snippet: #1 [babel-ts] format 2`] = `
+"Type parameters cannot appear on a constructor declaration. (1:22)
+> 1 | class A { constructor<a>() {} }
+    |                      ^
+Cause: Type parameters cannot appear on a constructor declaration. (1:21)"
+`;
+
 exports[`snippet: #1 [oxc-ts] format 1`] = `
 "Expected \`,\` or \`]\` but found \`:\` (1:15)
 > 1 | type T = [x<y>: A];
     |               ^"
 `;
 
+exports[`snippet: #1 [oxc-ts] format 2`] = `
+"Type parameters cannot appear on a constructor declaration (1:22)
+> 1 | class A { constructor<a>() {} }
+    |                      ^^^"
+`;
+
 exports[`snippet: #1 [typescript] format 1`] = `
 "',' expected. (1:15)
 > 1 | type T = [x<y>: A];
diff --git a/tests/format/misc/errors/typescript/tuple/format.test.js b/tests/format/misc/errors/typescript/tuple/format.test.js
index e3c7026cf..c9b054812 100644
--- a/tests/format/misc/errors/typescript/tuple/format.test.js
+++ b/tests/format/misc/errors/typescript/tuple/format.test.js
@@ -17,6 +17,8 @@ runFormatTest(
     snippets: [
       // A required element cannot follow an optional element.
       "type T = [x?: A, y: B];",
+      // Type parameters cannot appear on a constructor declaration.
+      "class A { constructor<a>() {} }",
     ],
   },
   [
@@ -25,3 +27,18 @@ runFormatTest(
     "oxc-ts",
   ],
 );
+
+runFormatTest(
+  {
+    importMeta: import.meta,
+    snippets: [
+      // Type parameters cannot appear on a constructor declaration.
+      "class A { 'constructor'<a>() {} }",
+    ],
+  },
+  [
+    // "typescript",
+    "babel-ts",
+    // "oxc-ts",
+  ],
+);