`single_use_lifetimes`: false positive (suggests unstable anonymous lifetimes in `impl Trait`)

Consider this code (playground):

#[warn(single_use_lifetimes)]

// warning: lifetime parameter `'a` only used once
fn foo<'a>(x: impl IntoIterator<Item = &'a i32>) -> Vec<i32> {
  x.into_iter().copied().collect()
}

fn main() {
  foo(&[1, 2, 3]);
}

The warning is issued: warning: lifetime parameter `'a` only used once. However, removing the lifetime as suggested makes code to not compile:

#[warn(single_use_lifetimes)]

// error[E0658]: anonymous lifetimes in `impl Trait` are unstable
fn foo(x: impl IntoIterator<Item = &i32>) -> Vec<i32> {
  x.into_iter().copied().collect()
}

fn main() {
  foo(&[1, 2, 3]);
}

So the compiler contradicts itself.

I suspect single_use_lifetimes does not correctly verify whether the compiler feature is available. My understanding is that it will be stabilized in 2024 edition (https://github.com/rust-lang/rust/issues/117587).

rust-lang / rust

`single_use_lifetimes`: false positive (suggests unstable anonymous lifetimes in `impl Trait`) #129255

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