[bug] declaration files have invalid class member generics with mixin & multiple layer inheritance

[TechQuery]

🔎 Search Terms

declaration .d.ts invalid class member field generic mixin inherit

🕗 Version & Regression Information

• This changed between versions ______ and _______
• This changed in commit or PR _______
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________
• I was unable to test this on prior versions because _______

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/MYGwhgzhAEBCkFMA8AVAfNA3gKGn6EArgA4IBOAsggLYBG50AvFgL7STQrYvbAD2AOwgAXaBQCWAD3ECm0JABEwwsABpoAYXBRoCScIQCAJjAEIA7tAAUAOjtHlYAFzsBATwDaAXQCUTDPAQyEoqaGi4+FYAyiTkLlqQEH6MGKCJuvqGJtAxpGRYEfj41FIyVHQMzACMhdAsQA

💻 Code

class Base<T> {
    superMember = {} as T
}
const Mixin = <Data, Class extends new (...data: any[]) => Base<Data>>
    (Super: Class) => class extends Super {
        mixinMember = 1
    }

🙁 Actual behavior

declare class Base<T> {
    superMember: T;
}
declare const Mixin: <Data, Class extends new (...data: any[]) => Base<Data>>(Super: Class) => {
    new (...data: any[]): {
        mixinMember: number;
        superMember: T;  // invalid generic variable in .d.ts
    };
} & Class;

🙂 Expected behavior

tsc generates completely valid .d.ts files with mixin inheritance.

Additional information about the issue

No response