discarded_futures : Unwaited return for when Future is expected

[bsz0206]

Unwaited does work only on void returns. We are forced to ignore, which is not nice:

FutureBuilder(
// ignore: discarded_futures
future: asyncCall(),

Unwaited does work only on void returns:
FutureBuilder(
future: unawaited(asyncCall()),,

[devoncarew]

Thanks for the report; this repo is for proposals to add existing lints to our recommended lint set. You might want to re-file this at the dart-lang/sdk repo?

[bsz0206]

thanks. can you refer me to the page?

[lrhn]

The discarded_futures lint is causing a lot of confusion. It's name doesn't match it's description, and it's unclear which the implementation is matching, if either.

The description doesn't say that using unawaitedshould have any effect.
To turn off the lint, you should change the surrounding function to being async.

See #59204.

[FMorschel]

Hey @bsz0206, considering #59204, I've tested

import 'dart:async';

Future<void> f() async {}

void g() {
  unawaited(f());
}

And got no lint, so I think this can be closed?

---

If you have any other problems with the FutureBuilder widget, you may want to have a look at (which are all duplicates):

• discarded_futures lint false positive #59504
• Possible false positive in discarded_futures lint #58889
• update discarded_futures lint rule to not trigger when a widget expect a futur #59455
• [analyzer] False positives for discarded_futures when passing future-returning function call as an argument #59151
• discarded_futures false positive? #59387

[bsz0206]

No, the use case is different. The future functions returns something other than void:

Future getMeAnString() async {
/* ... */
}

FutureBuilder(
future: getMeAnString(),
builder: ..
...
)

then I would get: Asynchronous function invoked in a non-'async' function. Try converting the enclosing function to be 'async' and then 'await' the future. and I will have to add an //ignore :

FutureBuilder(
// ignore: discarded_futures
future: getMeAnString(),
builder: ..
...
)

This literally means almost every FutureBuilder would need an extra ignore that is not nice.

Hey @bsz0206, considering #59204, I've tested

import 'dart:async';

Future<void> f() async {}

void g() {
  unawaited(f());
}

And got no lint, so I think this can be closed?

[FMorschel]

Thanks for clarifying! Then this is the same as the other issues I mentioned. I'm working on a fix for this.

[FMorschel]

@pq here is the CL: https://dart-review.googlesource.com/c/sdk/+/403901

Once you review it, can you also take a look at all of the issues mentioned to make sure you agree they are dupes? Thanks!

[FMorschel]

I noticed that this should consider FutureOr. I'll review it later today. Also, I'll open another issue to address that it shows the unnawaited fix for FutureOr but that is not valid.