`util::local_poll_adapter::tests::deferred_success` test looks little bit too flaky

[motorailgun]

Problem

Test for utility LocalPollAdapter, util::local_poll_adapter::tests::deferred_success is failing multiple times on CI but re-running doesn't (or maybe sometimes does) reproduce the failure.

Recently failed runs:

• https://github.com/rust-lang/cargo/actions/runs/24542250922/job/71750398656
• https://github.com/rust-lang/cargo/actions/runs/24606774042/job/71954228414

Possible cause is that short waiting time here might be causing Future to immediately returning Ready:

cargo/src/cargo/util/local_poll_adapter.rs

Line 114 in 6ea2e71

futures_timer::Delay::new(Duration::from_millis(1)).await

and thus poll() returns Ready.

cargo/src/cargo/util/local_poll_adapter.rs

Lines 67 to 75 in 6ea2e71

	// Attempt to run the future immediately. If it has no `await` yields,
	// it will return here.
	if let Some((k, v)) = (&mut future).now_or_never() {
	if let Ok(success) = &v {
	// Only cache successful results.
	self.cache.insert(k, Poll::Ready(Ok(success.clone())));
	}
	return Poll::Ready(v);
	}

Steps

No response

Possible Solution(s)

No response

Notes

I can't reproduce this on local.

#!/bin/bash

set -xe

for i in `seq 100`
do
	echo test $i
	cargo test util::local_poll_adapter::tests::deferred_success
done

Version

CI, and local:

cargo 1.97.0-nightly (eb94155a9 2026-04-09)
release: 1.97.0-nightly
commit-hash: eb94155a9a60943bd7b1cb04abec42f5d0de6ddc
commit-date: 2026-04-09
host: x86_64-unknown-linux-gnu
libgit2: 1.9.2 (sys:0.20.4 vendored)
libcurl: 8.19.0-DEV (sys:0.4.87+curl-8.19.0 vendored ssl:OpenSSL/3.5.4)
ssl: OpenSSL 3.5.4 30 Sep 2025
os: Arch Linux [64-bit]

[weihanglo]

Thanks for creating this issue. Also affected #16867 (comment).

@rustbot label +A-testing-cargo-itself -S-triage +S-needs-design