Error when trying to assign a subclass of a base class with generics to typeof of that base class

[dummdidumm]

TypeScript Version: 4.1.2

Search Terms: class generic extends typeof 2322

I stumbled upon a type error when trying to assign a subclass of a base class with generics to typeof of that base class.

Code

declare class Base<T extends Record<string, any>> {
  a: T;

  constructor(a: T);
}

class Sub1 extends Base<{a: boolean}> {}

const error: typeof Base = Sub1;

// Silence error by adding another constructor definition:
declare class BaseWith2Constructors<T extends Record<string, any>> {
  a: T;

  constructor(a: T);
  constructor(a: T);
}

class Sub2 extends BaseWith2Constructors<{a: boolean}> {}

const noerror: typeof BaseWith2Constructors = Sub2;

Expected behavior:

I would expect the first assignment to not error as well.

Actual behavior:

I get error 2322. The error says Type 'T' is not assignable to type '{ a: boolean; }' and Property 'a' is missing in type 'Record<string, any>' but required in type '{ a: boolean; }' which sounds like the assignment checks are flipped.

Strangely enough, the error can be silenced by adding a second constructor definition. Is that a workaround I can rely on?

If this is expected behavior, how am I supposed to use the base class as common base in this example? I cannot do typeof Base<any> in this case because that's a syntax error.

Playground Link:

https://www.typescriptlang.org/play?ts=4.1.2#code/CYUwxgNghgTiAEkoGdnwEIpAHgCrxAA8AXEAO2DQCVwB7GYbZYmASzIHMAaeKMgTwB8g+AG8AsACh4vAFzxcAbilSZYWmWYwArmGL0AFFHm4AlMskBfFZKSp4AZW0AjAIwES5ShizZRx+GdaWggQPksRUWtJKXVNYgIYGHp5Yn4ABxBaADMfZAQAXkcXVwspAHpyx1ZQsjAEECT6QP5eYGB2Dl4yWmIAC0bEDS1dfRh4UGz2VmJWDVkpUCQ4RGh7THyAdRm+gCYAYWGWUfpkPA9SCmo6BiYWTp4+IUjVOQUy6SH4nT1DALMLGojj8xkYTOYpNFYms0E5nLsLl40BsQNt+gdgScYGd-PIgiEwmQImIobYjvAeo1kjBUhksrkUWi9odvli0EU4btFEA

Related Issues:

[RyanCavanaugh]

These should both be errors -- new error({ a: "" }) is a legal invocation that puts a string where a boolean is expected.

[dummdidumm]

Thanks for the quick reply, that makes sense. Is there a better way then to achieve what I want other than

class Genericbase extends Base<any> {}
const foo: typeof Genericbase = Sub

[RyanCavanaugh]

There are other ways to do it, but that's probably the best one.

[typescript-bot]

👋 Hi, I'm the Repro bot. I can help narrow down and track compiler bugs across releases! This comment reflects the current state of the repro in the issue body running against the nightly TypeScript.

---

Issue body code block by @dummdidumm

❌ Failed: -

• Type 'typeof Sub1' is not assignable to type 'typeof Base'. Types of construct signatures are incompatible. Type 'new (a: { a: boolean; }) => Sub1' is not assignable to type 'new >(a: T) => Base'. Types of parameters 'a' and 'a' are incompatible. Type 'T' is not assignable to type '{ a: boolean; }'. Property 'a' is missing in type 'Record' but required in type '{ a: boolean; }'.

Historical Information

Version

Reproduction Outputs

4.2.2, 4.3.2, 4.4.2, 4.5.2, 4.6.2

❌ Failed: - Type 'typeof Sub1' is not assignable to type 'typeof Base'. Types of construct signatures are incompatible. Type 'new (a: { a: boolean; }) => Sub1' is not assignable to type 'new <T extends Record<string, any>>(a: T) => Base<T>'. Types of parameters 'a' and 'a' are incompatible. Type 'T' is not assignable to type '{ a: boolean; }'. Property 'a' is missing in type 'Record<string, any>' but required in type '{ a: boolean; }'.