False positive: `cow` and `into_owned`

[Hofer-Julian]

Summary

When using a Cow type clippy warns about the usage of into_owned but it's suggested alternative doesn't work.

Lint Name

clippy::unnecessary_to_owned

Reproducer

I tried this code:

use std::borrow::Cow;

fn main() {
    test_function();
}

fn test_function() -> impl IntoIterator {
    let cow: Cow<'_, Vec<String>> = Cow::Owned(vec![String::from("example")]);

    // Suggestion which fails to compile
    // return cow.iter().cloned();

    cow.into_owned().into_iter()
}

I saw this happen:

unnecessary use of `into_owned`
for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_to_owned
`#[warn(clippy::unnecessary_to_owned)]` on by default

I expected to see this happen:

Either no warning, or a suggestion that works

Version

rustc 1.80.1 (3f5fd8dd4 2024-08-06)
binary: rustc
commit-hash: 3f5fd8dd41153bc5fdca9427e9e05be2c767ba23
commit-date: 2024-08-06
host: x86_64-unknown-linux-gnu
release: 1.80.1
LLVM version: 18.1.7

Additional Labels

No response

[samueltardieu]

This is indeed a false positive, as well as a false negative: it should have suggested to drop .into_iter().