Add note for to clarify trait restriction for function if we get (in my example "borrow as mutable" error)

[godcodehunter]

Code example
https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=63c770ffce3c7420dd845653f7250b9f
We can try brute force all implementation, dropping trait restriction:
for generic type
for concrete type
If we find some implementation which allow you to get rid of this error (or maybe from all errors).
We can provide note with candidates and fix for restriction

[rogday]

Simpler example:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=7040e3738585cb14b0cb77b017d5ef53
foobar is expected to fail with message about lack of restrictions on K

[estebank]

error[E0277]: the trait bound `K: Clone` is not satisfied
  --> src/lib.rs:10:30
   |
10 |     <Vec<_> as Clone>::clone(&v).drain(..);
   |     ------------------------ ^^ the trait `Clone` is not implemented for `K`
   |     |
   |     required by a bound introduced by this call
   |
   = note: required for `Vec<K>` to implement `Clone`
help: consider restricting type parameter `K`
   |
9  | fn bar<K: std::clone::Clone>(v: &Vec<K>) {
   |         +++++++++++++++++++

error[E0596]: cannot borrow data in a `&` reference as mutable
 --> src/lib.rs:4:5
  |
4 |     <&Vec<_> as Clone>::clone(&v).drain(..);
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable

error[E0596]: cannot borrow data in a `&` reference as mutable
  --> src/lib.rs:16:5
   |
16 |     v.clone().drain(..);
   |     ^^^^^^^^^^^^^^^^^^^ cannot borrow as mutable

We need to make E0596 suggest Clone.