`impl cmp::PartialEq<String> for Path` is recursive

[hkBst]

I tried this code:

use std::path::Path;
pub trait ParEq<Rhs = Self>
where
    Rhs: ?Sized,
{
    fn eq2(&self, other: &Rhs) -> bool;
}

impl ParEq<String> for Path {
    fn eq2(&self, other: &String) -> bool {
        self.eq2(&*other)
    }
}

fn main() {
    // &Path == &String
    Path::new("path") == &"path".to_string();
}

I expected to see this happen: works or compile error

Instead, this happened: runtime stack overflow

This is in current nightly. I believe this is due to the object of this clippy warning:

warning: function cannot return without recursing
    --> library/std/src/path.rs:3428:5
     |
3428 | /     fn eq(&self, other: &String) -> bool {
3429 | |         self == &*other
3430 | |     }
     | |_____^
     |
note: recursive call site
    --> library/std/src/path.rs:3429:9
     |
3429 |         self == &*other
     |         ^^^^^^^^^^^^^^^
     = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#unconditional_recursion
     = note: `-W clippy::unconditional-recursion` implied by `-W clippy::suspicious`
     = help: to override `-W clippy::suspicious` add `#[allow(clippy::unconditional_recursion)]`

[hkBst]

Code seems to have been introduced here: #140956

[cyrgani]

The same problem was already fixed for PathBuf (#146183), but apparently not for Path. As this is already present on beta, the fix should probably be backported too.

[el-ev]

@rustbot claim

[cuviper]

Rustc has it's own default-warn unconditional_recursion lint too -- I wonder why that didn't trigger here?

[cuviper]

See #146994 to add clippy's lint to CI.