This is technically correct since an object of type any could be a Promise. Perhaps there should be an option allowAny, on by default, that allows any to be used here?

While it might be technically correct, I don't see how it's ever wanted behavior for this rule. It would mean you would have to add async to anything that returns any, even originally synchronous functions.

Does the lint trigger on function a(): Promise<string> | string? I think the rule should only trigger when it definitely only returns promises, not when it could return a promise.

Edit: Never mind. This rule intends to solve functions 'either returning a Promise or something else' as well as 'returning a rejected Promise and throwing an error'.

If a function returns 'any', the user disables type checking in Typescript and relies on manually checked logic. I think the expected behaviour is thus that it doesn't lint in the specific case of any.

That’s why i suggested adding an option that would allow any by default but let the user disallow it. However, if it’s very unlikely to be a useful option, there’s no need to add it.

I've got the same problem with axios & class getters:

class Mine {
  public get t() {
    return Axios;
  }
}

This gets flagged as should be marked with async (which is actually not allowed with get).

Also seeing this in a webpack.config.js that has functions that return various configurations of webpack plugins, e.g.

(note: this is from a project that has a mixed codebase of JS and TS files, and the webpack config is Javascript)

function extractCss(hashFilename) {
	return new MiniCssExtractPlugin({filename: hashFilename ? "[name]-[chunkhash:6].css" : "[name].css"});
}

function defineAppConfig(maxDataAgeDays) {
	return new webpack.DefinePlugin({MAX_DATA_AGE_DAYS: maxDataAgeDays});
}

Both of the above functions trigger @typescript-eslint/promise-function-async, but as far as I can tell neither of these plugin constructors return any or Promise types?

I'm getting similar error on v1.13.0

import { Reducer } from 'redux';
const reducer: Reducer<Record<string, string>> = (state = {}, _action) => state;

Versions

have you tried the allowAny: false option?
Also if you try the 2.0 canary version, it should have the above option as the default value.

(closing as this didn't get closed when #553 was merged)