[no-floating-promises] Should not report on async IIFEs

[sindresorhus]

Repro

{
  "rules": {
    "@typescript-eslint/no-floating-promises": "error"
  }
}

(async () => {
	await something();
})();

Expected Result

I expected it not to report as it's an intentional action. It doesn't catch a mistake.

If you're not willing to add this exception by default, at least add an option to ignore async IIFEs.

Actual Result

It reports as a floating promise, which is technically correct, but not wanted behavior, at least from my perspective.

Additional Info

Versions

package	version
@typescript-eslint/eslint-plugin	1.11.0
@typescript-eslint/parser	1.11.0
TypeScript	3.5.1
ESLint	5.16.0
node	8.16.0
npm	6.9.0

[Jessidhia]

Using the void operator makes this explicit, and the promise does not count as floating: void (async () => { /* ... */ })()

[bradzacher]

I would be okay with this living as an option.

It is potentially a reportable error because you might be using an IIFE to enclose some logic + variables with the intention of awaiting the response. I've seen this pattern before because it saves you passing arguments in, and it avoids the locally scoped variables from leaking into the wider function.

Whilst you have intentionally done this pattern, it doesn't mean everyone will intentionally float a promise there.

[sindresorhus]

You're right. An option would be best.

[glen-84]

@Jessidhia,

Using the void operator makes this explicit, and the promise does not count as floating: void (async () => { /* ... */ })()

While this is true in TSLint (at least for now), it doesn't appear to work in ESLint. Would this be considered a bug, or an enhancement request?

Edit: I've just noticed the discussion in #495.