TS2589 regression in 6.0: implements without type parameters causes excessive type instantiation when property uses concrete generic type

🔎 Search Terms

Type instantiation is excessively deep and possibly infinite.

🕗 Version & Regression Information

• This changed between versions 5.9.3 and 6.0.2

⏯ Playground Link

https://www.typescriptlang.org/play/?target=7#code/JYWwDg9gTgLgBDAnmApnA3nAShArjFKAGQgGMBDGYCAOwBo4B1FAIwGEJxaUaYBJXoQBm5UmgC+cIVE5wARAAEAbuXIATYDQD0M-ITkBuAFBGkqbHgIBRAB7wAvBjgBnFKSq0A-AC4XMKJoA5nDixkZaWnAAKgDKAEwArAAcAJxwtAgAFmikADbkzs5wam75UJTUNHAsKLkQAO4AdOGRAGLANr5QKGD5YnAABszsnJA0PPyCUCJiA3D1wDCZg8McXOO8AgTToigAPDh6tjAAfAPNES1wAHIQBL5LaIQyUOk0uYgIAYGBhEU1FFwrkGdQoHhoc2ARTMKDU80Wy3IcFItFI3QICGQKCuYHI5RAKG2cAAFANDtsSGDKgdLChjmcAJSNOAAVWcQUG5MIlIqtDmCyWljgSJhOLx5AJRLUEBQRRody+wB+hDgi2aKBskFgyPyhTgAFlEFZcigCbw4BqCDQ1EUABJRfVEY2miaq8Ams0wIqrUbcTZTGZodBGOBwUG8mg+Cx6YhkCM0o52E7GcRGIA

💻 Code

import type { RouterLocation, WebComponentInterface } from "@vaadin/router";

type RouteExt = { section?: string };

// TS2589 on the class declaration below.
// Fix: replace `WebComponentInterface` with `WebComponentInterface<RouteExt>`.
//
// Note: the error only triggers because `location` is typed with a concrete type
// parameter (`RouterLocation<RouteExt>`). Using `RouterLocation` without a type
// parameter does not trigger it.
export class MyElement extends HTMLElement implements WebComponentInterface {
  location?: RouterLocation<RouteExt>;
}

🙁 Actual behavior

I get this error:

Type instantiation is excessively deep and possibly infinite.

But the information isn't very useful to know what to do exactly in this case.

🙂 Expected behavior

Ideally no error, otherwise some more pointers about how to fix this.

Additional information about the issue

When running with --extendedDiagnostics:

typescript 5.9.3:

     Files:                         259
     Types:                      203241
     Instantiations:            2593860

typescript 6.0.2:

     Files:                         259
     Types:                      217322
     Instantiations:            5379836

Bắt đầu với Playground được liên kết và so sánh TypeScript 5.9.3 với 6.0.2 bằng --extendedDiagnostics, tập trung vào khai báo implements và thuộc tính RouterLocation cụ thể. Truy vết đường dẫn khởi tạo kiểu chịu trách nhiệm cho TS2589 và xác thực kết quả dựa trên reproduction được cung cấp; được xem là hoàn tất khi ví dụ không còn báo lỗi hoặc cung cấp hướng dẫn có tính khả thi hơn.