FP cloned_instead_of_copied: explicit Iter::Cloned, HRTBs

Summary

.

Lint Name

cloned_instead_of_copied

Reproducer

I tried this code:

// Tests that HRTBs are correctly accepted -- https://github.com/rust-lang/rust/issues/50301
// check-pass
trait Trait
where
    for<'a> &'a Self::IntoIter: IntoIterator<Item = u32>,
{
    type IntoIter;
    fn get(&self) -> Self::IntoIter;
}

struct Impl(Vec<u32>);

impl Trait for Impl {
    type IntoIter = ImplIntoIter;
    fn get(&self) -> Self::IntoIter {
        ImplIntoIter(self.0.clone())
    }
}

struct ImplIntoIter(Vec<u32>);

impl<'a> IntoIterator for &'a ImplIntoIter {
    type Item = <Self::IntoIter as Iterator>::Item;
    type IntoIter = std::iter::Cloned<std::slice::Iter<'a, u32>>;
    fn into_iter(self) -> Self::IntoIter {
        (&self.0).into_iter().cloned()
    }
}

fn main() {
}

I saw this happen:
cargo clippy --fix -- -Aclippy::all -Wclippy::cloned_instead_of_copied

    Checking clpy v0.1.0 (/tmp/clpy)
warning: failed to automatically apply fixes suggested by rustc to crate `clpy`

after fixes were automatically applied the compiler reported errors within these files:

  * src/main.rs

This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag

The following errors were reported:
error[E0308]: mismatched types
  --> src/main.rs:26:9
   |
25 |     fn into_iter(self) -> Self::IntoIter {
   |                           -------------- expected `std::iter::Cloned<std::slice::Iter<'_, u32>>` because of return type
26 |         (&self.0).into_iter().copied()
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `std::iter::Cloned`, found struct `std::iter::Copied`
   |
   = note: expected struct `std::iter::Cloned<std::slice::Iter<'_, u32>>`
              found struct `std::iter::Copied<std::slice::Iter<'_, u32>>`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
Original diagnostics will follow.

warning: used `cloned` where `copied` could be used instead
  --> src/main.rs:26:31
   |
26 |         (&self.0).into_iter().cloned()
   |                               ^^^^^^ help: try: `copied`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#cloned_instead_of_copied
   = note: requested on the command line with `-W clippy::cloned-instead-of-copied`

warning: `clpy` (bin "clpy") generated 1 warning (run `cargo fix --bin "clpy"` to apply 1 suggestion)
warning: `clpy` (bin "clpy" test) generated 1 warning (1 duplicate)
    Finished dev [unoptimized + debuginfo] target(s) in 0.19s

Version

rustc 1.67.0-nightly (c5d82ed7a 2022-11-19)
binary: rustc
commit-hash: c5d82ed7a4ad94a538bb87e5016e7d5ce0bd434b
commit-date: 2022-11-19
host: x86_64-unknown-linux-gnu
release: 1.67.0-nightly
LLVM version: 15.0.4

Additional Labels

No response

Start with the cloned_instead_of_copied lint and reproduce the report using the provided Rust example and cargo clippy command. Trace why the suggestion changes an explicitly declared std::iter::Cloned return type to Copied; done means the lint no longer emits an invalid fix for this HRTB case.