Wrong declaration file for generic class factory

TypeScript Version: 2.5.2

Code
I created some code to ensure that developer will create only one class with specific 'kind' property used in discriminated union:

const kindCache: { [kind: string]: boolean } = {};

function register(kind: string): void | never {
  if (kindCache[kind]) {
    throw new Error(`Class with kind "${kind}" is already registered.`);
  }
  kindCache[kind] = true;
}

function ClassFactory<TKind extends string>(kind: TKind) {
  register(kind);

  return class {
    static readonly THE_KIND: TKind = kind;
    readonly kind: TKind = kind;
  };
}

class Kinds {
  static readonly A = "A";
  static readonly B = "B";
  static readonly C = "C";
}

export class AKind extends ClassFactory(Kinds.A) {
}

export class BKind extends ClassFactory(Kinds.B) {
}

export class CKind extends ClassFactory(Kinds.C) {
}

Locally it works as expected. Compilation of:

const x: AKind = new BKind();

causes error:

 error TS2322: Type 'BKind' is not assignable to type 'AKind'.
  Types of property 'kind' are incompatible.
    Type '"B"' is not assignable to type '"A"'.

Expected behavior:
I expected that it will generate d.ts like this:

declare const AKind_base: {
    new (): {
        readonly kind: "A";
    };
    readonly THE_KIND: "A";
};
export declare class AKind extends AKind_base {
}
declare const BKind_base: {
    new (): {
        readonly kind: "B";
    };
    readonly THE_KIND: "B";
};
export declare class BKind extends BKind_base {
}
declare const CKind_base: {
    new (): {
        readonly kind: "C";
    };
    readonly THE_KIND: "C";
};
export declare class CKind extends CKind_base {
}

Actual behavior:
But type of non-static field is invalid (TKind)

declare const AKind_base: {
    new (): {
        readonly kind: TKind;
    };
    readonly THE_KIND: "A";
};
export declare class AKind extends AKind_base {
}
declare const BKind_base: {
    new (): {
        readonly kind: TKind;
    };
    readonly THE_KIND: "B";
};
export declare class BKind extends BKind_base {
}
declare const CKind_base: {
    new (): {
        readonly kind: TKind;
    };
    readonly THE_KIND: "C";
};
export declare class CKind extends CKind_base {
}

Aluan Haddad (@aluanhaddad)

Aluan Haddad (@aluanhaddad) it will produce the wrong d.ts as well

export declare type Kind = 'A' | 'B' | 'C';
export declare function ClassFactory<TKind extends Kind>(kind: TKind): {
    new (): {
        readonly kind: TKind;
    };
    readonly THE_KIND: TKind;
};
declare const AKind_base: {
    new (): {
        readonly kind: TKind;
    };
    readonly THE_KIND: "A";
};
export declare class AKind extends AKind_base {
}
declare const BKind_base: {
    new (): {
        readonly kind: TKind;
    };
    readonly THE_KIND: "B";
};
export declare class BKind extends BKind_base {
}
declare const CKind_base: {
    new (): {
        readonly kind: TKind;
    };
    readonly THE_KIND: "C";
};
export declare class CKind extends CKind_base {
}

Here's a simpler reproduction:

export function withMixin<S>(superclass: S): S {
  return superclass;
}

export class Base<T> {
  constructor(value: T) {
  }
}

export class MixedTogether<T> extends withMixin<new (value: T) => Base<T>>(Base){}

and the resulting (broken) d.ts:

export declare function withMixin<S>(superclass: S): S;
export declare class Base<T> {
    constructor(value: T);
}
declare const MixedTogether_base: new (value: T) => Base<T>;
export declare class MixedTogether<T> extends MixedTogether_base {
}
// Any code that depends on this module will now throw:
//     error TS2304: Cannot find name 'T'.
// even though the module itself built cleanly

Fix microsoft#18545, dont use declared type of class expression

Fix instantiated generic mixin declaration emit (#19144)

Port master into release-2.6 10/16 (#19237)

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Wrong declaration file for generic class factory #18545

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Wrong declaration file for generic class factory #18545

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damian-lewkowicz commented on Sep 18, 2017

appsforartists commented on Sep 28, 2017

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