Duplicate trait suggestion

[DKenefake]

Given the following code: here

fn rot<T : std::ops::Shl<Output = T>>(x:&T, k:u32) -> T {
    let bit_count = std::mem::size_of::<T>() << 3;
    (x << k as T) | (x >> (bit_count - k as T))
}

The current output is:

error[E0369]: no implementation for `&T << T`
  --> src\lib.rs:10:8
   |
10 |     (x << k as T) | (x >> (bit_count - k as T))
   |      - ^^ ------ T
   |      |
   |      &T
   |
help: consider further restricting this bound
   |
8  | fn rot<T : std::ops::Shl<Output = T> + std::ops::Shl<Output = T>>(x:&T, k:u32) -> T {
   |                                      +++++++++++++++++++++++++++

The code is incorrect and shouldn't compile, but the suggestion is to duplicate a trait restriction that is already present in the function and can be repeated n-times, e.g. with T: std::ops::Shl<Output = T> + std::ops::Shl<Output = T> it will suggest T: std::ops::Shl<Output = T> + std::ops::Shl<Output = T>+ std::ops::Shl<Output = T>. This appears to indicate that the traits are not being checked correctly for suggestions, suggesting trait restrictions that are already present. The same output occurs in the nightly build.

[BGR360]

@rustbot label +D-invalid-suggestion