Should `map_clone` trigger on copies of double references?

[Manishearth]

fn main() {
    let x = Some(&"abcd");
    let y = x.map(|&p| p);
}

playpen

warning: You are using an explicit closure for cloning elements
 --> src/main.rs:3:13
  |
3 |     let y = x.map(|&p| p);
  |             ^^^^^^^^^^^^^ help: Consider calling the dedicated `cloned` method: `x.cloned()`
  |
  = note: #[warn(clippy::map_clone)] on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#map_clone

So map_clone triggers even for copies, which makes sense, since cloned() works on copies. Here it specificially is triggering on copies of a double reference.

However, we also have clone_double_ref which warns about cloning &&T since that may not do what one expected.

Also .map(|&x| x) is much clearer than .cloned() in such cases, it's not at all obvious that the .cloned() is there to unwrap a reference

I feel that this is a false positive, but I can see others disagreeing. Thoughts?

h/t @hawkw

[oli-obk]

Note that there's also .copied() which would make it much clearer that there's not heavy duty code happening.

[Manishearth]

In that case we should definitely suggest that whenever possible.

[Manishearth]

Fixed in #3970, but we can't land that until .copied() stabilizes.

[Centril]

.copied was stabilized in 1.36.0.

[Manishearth]

Sweet, put next steps here: #4043