TypeScript Version: 4.0.0-dev.20200512

Search Terms: jsdoc, declaration, varargs

Code

clazz.js:

export class Clazz {
  /**
   * @param {function(this:Object, ...*):*} functionDeclaration
   */
  method(functionDeclaration) {}
}

tsconfig.json:

{
  "compilerOptions": {
    "outDir": "lib",
    "declaration": true,
    "allowJs": true,
    "checkJs": true
  },
  "files": [
    "clazz.js"
  ]
}

Expected behavior:
The emitted declaration file is:

export class Clazz {
    /**
     * @param {function(this:Object, ...*):*} functionDeclaration
     */
    method(functionDeclaration: (...args: any[]) => any): void;
}

Actual behavior:

export class Clazz {
    /**
     * @param {function(this:Object, ...*):*} functionDeclaration
     */
    method(functionDeclaration: (args: any, ...args: any[]) => any): void;
}

Subsequent usages of a composite project break, as args is duplicated in the method argument types.

Note that removal of this:Object fixes the issue. Also, the following properly emits:

export class Clazz {
  /**
   * @param {function(this:Object, ...*):T} functionDeclaration
   * @template T
   */
  method(functionDeclaration) {}
}

Note here that the T is unused in the function, but it fixes the emitted declaration file.

Playground Link:

Related Issues: #38242 (we are successfully able to compile DevTools with the above workaround and the fix for #38242)