JSDoc with @extends, type parameter and member expression gives wrong dts output

🔎 Search Terms

jsdoc type parameter generics extends superclass template

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about JSDoc type parameters with @extends

I tried with TypeScript 5.0.0, 5.6.2, and 5.7.0-dev.20241001.

⏯ Minimal repro link

I needed more than one file to reproduce, which I can't do on the playground. Here's a simple reproducer:

https://github.com/blutorange/issue-repro/tree/issue-typescript-missing-type-param

git clone https://github.com/blutorange/issue-repro
cd issue-repro
git checkout issue-typescript-missing-type-param
npm install
npm run build

Then open dist/index.d.ts.

💻 Code

/**
 * @template {0|1|2} T
 * @extends {Scope.sub.Box<T>}
 */
export class MyComponent extends Scope.sub.Box {
    more() {
        return "foo";
    }
}

🙁 Actual behavior

The class in the extends clause is missing the type parameter. This is a compile error when you validate the .d.ts file.

declare const MyComponent_base: typeof import("./header.js").Box;
/**
 * @template {0|1|2} T
 * @extends {Scope.sub.Box<T>}
 */
export class MyComponent<T extends 0 | 1 | 2> extends MyComponent_base {
    constructor();
    more(): string;
}
export {};

🙂 Expected behavior

TypeScript should include the type parameter in the extends clause.

declare const MyComponent_base: typeof import("./header.js").Box;
/**
 * @template {0|1|2} T
 * @extends {Scope.sub.Box<T>}
 */
export class MyComponent<T extends 0 | 1 | 2> extends MyComponent_base<T> {
    constructor();
    more(): string;
}
export {};

Additional information about the issue

Only seems to happen when the extends clause is a member expression where TS generate an intermediate declare const ....

Fyi, I came across this issue while investigating how to setup a project for generating type declarations from js files for primefaces/primefaces#12500

Start with the linked reproducer by checking out issue-typescript-missing-type-param, running npm install and npm run build, then inspect dist/index.d.ts. Trace the declaration-emission path for a JSDoc @extends member expression; done means the generated extends clause retains the T type argument and the declaration validates.