Do not propose to remove async move if variables are captured by ref

[samueltardieu]

Fixes #10482

changelog: FP [redundant_async_block] Do not propose to remove async move if variables are captured by ref

[rustbot]

r? @xFrednet

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[samueltardieu]

The captured_by_ref() function can have false positives, but this errs on the safe side.

[OliverNChalk]

Is there an estimated release date for this, our codebase is running into this quite a bit when we launch tasks to drive components

[cynecx]

This fix is rather incomplete because CaptureBy::Ref can also move a value into the closure:

use std::future::Future;

async fn work(_: &str) {}

fn spawn(_: impl Future<Output = ()> + 'static) {}

fn main() {
    let val = "Hello World".to_owned();
    spawn(async { work(&{ val }).await }); // false-positive
}

[samueltardieu]

Indeed, fixed.

[samueltardieu]

I also propose to put the lint in nursery for the time being, notably because of #10509.

[xFrednet]

Hey, thank you for the PR and comments left by others. I'll sadly be busy until the end of the week, but you'll get a review by the end of next week :)

[xFrednet]

Generally looks good to me, I have a few questions, regarding names and documentation, but I'd say this is ready, once they've been cleared up.

Thank you for your patience, while waiting for the review :)

[xFrednet]

Looks good to me, thank you!

@bors r+

I've added the beta-nominated label. It looks like the lint has a few FP and changing the lint group should be able to land before the next release :)

[bors]

📌 Commit 3497086 has been approved by xFrednet

It is now in the queue for this repository.

[bors]

⌛ Testing commit 3497086 with merge 5839621...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: xFrednet
Pushing 5839621 to master...

[flip1995]

This will make it into the same release as the commit that added the lint. No action required.