Generated .d.ts files from JS project are invalid

[Gozala]

TypeScript Version: 3.7.x-dev.201xxxxx

Search Terms:

Code

lib.js

/**
 * @template T
 * @implements {IEncoder<T>}
 */
export class Encoder {
  /**
   * @param {T} value 
   */
  encode(value) {
    return new Uint8Array(0)
  }
}


/**
 * @template T
 * @typedef {import('./interface').Encoder<T>} IEncoder
 */

interface.ts

export interface Encoder<T> {
  encode(value:T): Uint8Array
}

Expected behavior:

Generating typedefs should generate TS file that type checks, e.g. for lib.js it should produce something like:

/**
 * @template T
 * @implements {IEncoder<T>}
 */
export class EncoderImpl<T> implements IEncoder<T> {
    /**
     * @param {T} value
     */
    encode(value: T): Uint8Array;
}

import { Encoder as IEncoder } from "./interface"

Actual behavior:

Instead tsc generates lib.d.ts file which does not type check, because type parameters are omitted

/**
 * @template T
 * @implements {IEncoder<T>}
 */
export class EncoderImpl<T> implements Encoder {
    /**
     * @param {T} value
     */
    encode(value: T): Uint8Array;
}
export type IEncoder<T> = import("./interface").Encoder<T>;

Playground Link:

Can't make a playground link because it requires multiple files, but here is the repo with the above example
https://github.com/Gozala/tsc-implements-bug

Related Issues:

Unfortunately it's not just that type parameters are omitted, but also the fact that importing interface turns it into a type which then can't be used as implements target.