Cargo clone_on_copy false positive or bad suggestion

Lint name: clone_on_copy

I tried this code:

    #[test]
    fn copy_on_clone_false_positive() {
        let mut empty = [];
        let mut array = [0, 1];
        assert_eq!(
            (&mut empty[..], &mut array.clone()[..]),
            array.split_at_mut(0)
        );
    }

$ cargo clippy --all-targets

I expected to see this happen: No warning.

Instead, this happened: This warning:

warning: using `clone` on type `[i32; 2]` which implements the `Copy` trait
   --> src/file.rs:470:35
    |
470 |             (&mut empty[..], &mut array.clone()[..]),
    |                                   ^^^^^^^^^^^^^ help: try removing the `clone` call: `array`
    |
    = note: `#[warn(clippy::clone_on_copy)]` on by default
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#clone_on_copy

warning: 1 warning emitted

When I apply the suggested fix:

    #[test]
    fn copy_on_clone_false_positive() {
        let mut empty = [];
        let mut array = [0, 1];
        assert_eq!(
            (&mut empty[..], &mut array[..]),
            array.split_at_mut(0)
        );
    }

It no longer compiles:

error[E0499]: cannot borrow `array` as mutable more than once at a time
   --> src/file.rs:469:54
    |
469 |         assert_eq!((&mut empty[..], &mut array[..]), array.split_at_mut(0));
    |         ---------------------------------------------^^^^^------------------
    |         |                                |           |
    |         |                                |           second mutable borrow occurs here
    |         |                                first mutable borrow occurs here
    |         first borrow later used here

Meta

• cargo clippy -V: clippy 0.1.52 (9bc8c42b 2021-05-09)
• rustc -Vv:

rustc 1.52.1 (9bc8c42bb 2021-05-09)
binary: rustc
commit-hash: 9bc8c42bb2f19e745a63f3445f1ac248fb015e53
commit-date: 2021-05-09
host: x86_64-apple-darwin
release: 1.52.1
LLVM version: 12.0.0

Start with the clone_on_copy lint implementation and reproduce the example with cargo clippy --all-targets. Check why removing clone creates the reported mutable-borrow error, then add a regression test covering this case and confirm the diagnostic no longer suggests the invalid change.