`unnecessary_to_owned` in conjunction with reference counted slices and iterators

[SLUCHABLUB]

Summary

When trying to return an iterator over values in an Rc<[T]> that is owned by the function by first converting it to a Vec, the unnecessary_to_owned lint gets triggered. Clippy also suggested a "fix" which wouldn't compile.

error from clippy's suggested code:

error[E0716]: temporary value dropped while borrowed
  --> src/main.rs:13:5
   |
13 |       rc_slice_provider()
   |       -^^^^^^^^^^^^^^^^^^
   |       |
   |  _____creates a temporary value which is freed while still in use
   | |
14 | |         .iter()
15 | |         .copied()
   | |_________________- opaque type requires that borrow lasts for `'static`
16 |   }
   |   - temporary value is freed at the end of this statement

Lint Name

unnecessary_to_owned

Reproducer

I tried this code:

#![deny(clippy::unnecessary_to_owned)]

use std::rc::Rc;

#[derive(Copy, Clone)]
struct Foo;

fn rc_slice_provider() -> Rc<[Foo]> {
    Rc::from([Foo])
}

fn iterator_provider() -> impl Iterator<Item = Foo> {
    rc_slice_provider()
        .to_vec() // can't return a reference since the rc is owned by the function
        .into_iter()
}

I saw this happen:

error: unnecessary use of `to_vec`
  --> src/main.rs:13:5
   |
13 | /     rc_slice_provider()
14 | |         .to_vec() // can't return a reference since the rc is owned by the function
15 | |         .into_iter()
   | |____________________^ help: use: `rc_slice_provider().iter().copied()`
   |

I expected to see this happen:

Nothing I suppose. (You could technically create a user-defined iterator that takes ownership of the rc to avoid the reallocation so I guess the lint is somewhat warranted)

Version

example ran in playground but here is my local:

rustc 1.84.1 (e71f9a9a9 2025-01-27)
binary: rustc
commit-hash: e71f9a9a98b0faf423844bf0ba7438f29dc27d58
commit-date: 2025-01-27
host: aarch64-apple-darwin
release: 1.84.1
LLVM version: 19.1.5

Additional Labels

No response