`clippy::redundant-async-block` causes lifetime mismatch

Using the following flags

--force-warn clippy::redundant-async-block

this code:

use core::hash::{BuildHasher, BuildHasherDefault};

fn compute_max_collisions(name: &str, hasher: impl BuildHasher) {
    let table_mask = (1 << 17) - 1;
    let mut table_orig_order = vec![0u64; 1 << 17];
    let mut table_swap_order = vec![0u64; 1 << 17];
    for krate in 0..64_u32 {
        for def_index in 0..1024_u32 {
            let h_orig = hasher.hash_one(((def_index as u64) << 32) | krate as u64);
            let h_swap = hasher.hash_one(((krate as u64) << 32) | def_index as u64);
            table_orig_order[(h_orig & table_mask) as usize] += 1;
            table_swap_order[(h_swap & table_mask) as usize] += 1;
        }
    }
    
    let max_orig = table_orig_order.into_iter().max().unwrap();
    let max_swap = table_swap_order.into_iter().max().unwrap();
    println!("{name} max orig collisions: {max_orig}");
    println!("{name} max swap collisions: {max_swap}");
}

fn assert_future_unit_covariant_workaround<'s>(
    f: impl Future<Output = &'static ()> + 'static,
) -> impl Future<Output = &'s ()> + 's {
    // this works
    async move { f.await }
}

caused the following diagnostics:

    Checking _c562ca7861133a3f34c92e33f4b3dfde571553ec v0.1.0 (/tmp/icemaker_global_tempdir.GToAtTsoC3qp/icemaker_clippyfix_tempdir.z8myuo9KkZEY/_c562ca7861133a3f34c92e33f4b3dfde571553ec)
warning: this async expression only awaits a single future
  --> src/lib.rs:26:5
   |
26 |     async move { f.await }
   |     ^^^^^^^^^^^^^^^^^^^^^^ help: you can reduce it to: `f`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_async_block
   = note: requested on the command line with `--force-warn clippy::redundant-async-block`

warning: `_c562ca7861133a3f34c92e33f4b3dfde571553ec` (lib) generated 1 warning (run `cargo clippy --fix --lib -p _c562ca7861133a3f34c92e33f4b3dfde571553ec` to apply 1 suggestion)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.21s

However after applying these diagnostics, the resulting code:

use core::hash::{BuildHasher, BuildHasherDefault};

fn compute_max_collisions(name: &str, hasher: impl BuildHasher) {
    let table_mask = (1 << 17) - 1;
    let mut table_orig_order = vec![0u64; 1 << 17];
    let mut table_swap_order = vec![0u64; 1 << 17];
    for krate in 0..64_u32 {
        for def_index in 0..1024_u32 {
            let h_orig = hasher.hash_one(((def_index as u64) << 32) | krate as u64);
            let h_swap = hasher.hash_one(((krate as u64) << 32) | def_index as u64);
            table_orig_order[(h_orig & table_mask) as usize] += 1;
            table_swap_order[(h_swap & table_mask) as usize] += 1;
        }
    }
    
    let max_orig = table_orig_order.into_iter().max().unwrap();
    let max_swap = table_swap_order.into_iter().max().unwrap();
    println!("{name} max orig collisions: {max_orig}");
    println!("{name} max swap collisions: {max_swap}");
}

fn assert_future_unit_covariant_workaround<'s>(
    f: impl Future<Output = &'static ()> + 'static,
) -> impl Future<Output = &'s ()> + 's {
    // this works
    f
}

no longer compiled:

    Checking _c562ca7861133a3f34c92e33f4b3dfde571553ec v0.1.0 (/tmp/icemaker_global_tempdir.GToAtTsoC3qp/icemaker_clippyfix_tempdir.z8myuo9KkZEY/_c562ca7861133a3f34c92e33f4b3dfde571553ec)
error: lifetime may not live long enough
  --> src/lib.rs:26:5
   |
22 | fn assert_future_unit_covariant_workaround<'s>(
   |                                            -- lifetime `'s` defined here
...
26 |     f
   |     ^ returning this value requires that `'s` must outlive `'static`

error: could not compile `_c562ca7861133a3f34c92e33f4b3dfde571553ec` (lib test) due to 1 previous error
warning: build failed, waiting for other jobs to finish...
error: could not compile `_c562ca7861133a3f34c92e33f4b3dfde571553ec` (lib) due to 1 previous error

Version:

rustc 1.95.0-nightly (75963ce79 2026-01-25)
binary: rustc
commit-hash: 75963ce795666bc1f961e5d60060809809f6bc68
commit-date: 2026-01-25
host: x86_64-unknown-linux-gnu
release: 1.95.0-nightly
LLVM version: 21.1.8

Reproduce the issue with the example in src/lib.rs using --force-warn clippy::redundant-async-block, then run cargo clippy --fix --lib to inspect the suggested change. Compare the original and rewritten functions and verify that the resulting code still compiles without the lifetime mismatch.