Error message suggests to use a Box to wrap dyn Trait when it's unnecessary

Code

use std::io::Write;

fn foo(f: Option<&mut dyn Write>) {
    if let Some(f) = f {
        writeln!(f, "Hello").unwrap();
    }
}

fn bar() {
    let mut out = Some(std::io::stdout());
    foo(out.as_mut());
}

Current output

error[E0308]: mismatched types
  --> src/lib.rs:11:9
   |
11 |     foo(out.as_mut());
   |     --- ^^^^^^^^^^^^ expected `Option<&mut dyn Write>`, found `Option<&mut Stdout>`
   |     |
   |     arguments to this function are incorrect
   |
   = note: expected enum `Option<&mut dyn std::io::Write>`
              found enum `Option<&mut Stdout>`
   = help: `Stdout` implements `Write` so you could box the found value and coerce it to the trait object `Box<dyn Write>`, you will have to change the expected type as well
note: function defined here
  --> src/lib.rs:3:4
   |
3  | fn foo(f: Option<&mut dyn Write>) {
   |    ^^^ -------------------------

Desired output

= help: `Stdout` implements `Write` so you could make a reference to the found value and coerce it to the trait object `&mut dyn Write` or `Box<&dyn Write>`, you will have to change the expected type as well

Rationale and extra context

I can make it compile without using a Box.

fn bar() {
    let mut out = Some(std::io::stdout());
    foo(out.as_mut().map(|p| p as &mut dyn Write));
}

I don't think error message should suggest to use a Box when it's not necessary.

Also maybe it's just me but I'm not quite sure what you will have to change the expected type as well means.

Other cases

No response

Rust Version

$ rustc --version --verbose
rustc 1.80.1 (3f5fd8dd4 2024-08-06)
binary: rustc
commit-hash: 3f5fd8dd41153bc5fdca9427e9e05be2c767ba23
commit-date: 2024-08-06
host: x86_64-unknown-linux-gnu
release: 1.80.1

Anything else?

No response

Start by compiling the reproducer in src/lib.rs with the reported Rust version and compare the current diagnostic with the desired help text. Trace the compiler diagnostic that suggests boxing a dyn Write value, then update its wording and add coverage for the Option<&mut dyn Write> case; done means the output no longer unnecessarily recommends Box and clearly explains the reference coercion.