Suggest to swap a struct and a trait in trait impls where appropriate

[hkmatsumoto]

Given the following code: Playground

pub trait Trait {}

pub struct Struct {}

impl Struct for Trait {}

The current output is:

error[E0404]: expected trait, found struct `Struct`
 --> src/lib.rs:5:6
  |
5 | impl Struct for Trait {}
  |      ^^^^^^ not a trait

warning: trait objects without an explicit `dyn` are deprecated
 --> src/lib.rs:5:17
  |
5 | impl Struct for Trait {}
  |                 ^^^^^ help: use `dyn`: `dyn Trait`
  |
  = note: `#[warn(bare_trait_objects)]` on by default
  = warning: this is accepted in the current edition (Rust 2018) but is a hard error in Rust 2021!
  = note: for more information, see issue #80165 <https://github.com/rust-lang/rust/issues/80165>

[compiler-errors]

@TaKO8Ki, you have a lot of claimed issues. are you working on this?

[TaKO8Ki]

@compiler-errors I'm working on this issue. However, I have some issues I'm not working on, so I will unassign me from them.

[compiler-errors]

Okay, just be aware that holding onto many issues for months may discourage others from working on open issues like this.