Type definitions are wrong, don't allow Promise to be returned (caught by @typescript-eslint)

Env:

TypeScript: 4.1.3
Express: 4.17.1
Node: 14.16.0
@typescript-eslint/eslint-plugin: 4.17.0
@typescript-eslint/parser: 4.17.0

Repro:

import express from 'express';
import createRouter from 'express-promise-router';

export const router = createRouter();

router.get(
  '/',
  async (req: express.Request, res: express.Response): Promise<string> => {
    res.sendStatus(200);
  },
);

export const server = express().use(router);

Produces:

Promise returned in function argument where a void return was expected.eslint@typescript-eslint/no-misused-promises

This is because the type definitions from express-promise-router are just using the express.Router interface which doesn’t support Promises (the very reason why this package exists).

[mormahr]

There is nothing to merge. I wrote a failing test case but actually solving this isn’t trivial as (as far as I can tell) we need to duplicate lots of definitions from @types/express. I haven’t had the time to look into this again since then.

[mormahr]

I think i understand what you mean now. It’s not a TypeScript error, it’s that ts eslint thinks the promise is unused. I’ll have a look later.