... cannot be unpinned diagnostic uses a wrong span

[WaffleLapkin]

Given the following code: (playground)

use tokio::io::{self, AsyncRead};
use tokio::fs::File;

async fn f(mut r: impl AsyncRead) -> Result<(), ()> {
    let mut file = File::open("").await.map_err(drop)?;

    io::copy(&mut r, &mut file).await.map_err(drop)?;

    Ok(())
}

The current output is:

error[E0277]: `impl AsyncRead` cannot be unpinned
   --> src/lib.rs:7:22
    |
7   |     io::copy(&mut r, &mut file).await.map_err(drop)?;
    |     --------         ^^^^^^^^^ the trait `Unpin` is not implemented for `impl AsyncRead`
    |     |
    |     required by a bound introduced by this call
    |
    = note: consider using `Box::pin`
note: required by a bound in `tokio::io::copy`
   --> /playground/.cargo/registry/src/github.aaakk.us.kg-1ecc6299db9ec823/tokio-1.11.0/src/io/util/copy.rs:143:24
    |
143 |         R: AsyncRead + Unpin + ?Sized,
    |                        ^^^^^ required by this bound in `tokio::io::copy`
help: consider further restricting this bound
    |
4   | async fn f(mut r: impl AsyncRead + std::marker::Unpin) -> Result<(), ()> {
    |                                  ++++++++++++++++++++

The error mentions impl AsyncRead (ie the &mut r argument), but points to the other argument (&mut file, tokio::fs::File).

[WaffleLapkin]

MRE: (playground)

fn copy<R: Unpin, W>(_: R, _: W) {}

fn f<T>(r: T) {
    let w = ();
    copy(r, w);
}

error[E0277]: `T` cannot be unpinned
 --> src/lib.rs:5:13
  |
5 |     copy(r, w);
  |     ----    ^ the trait `Unpin` is not implemented for `T`
  |     |
  |     required by a bound introduced by this call
  |
  = note: consider using `Box::pin`
note: required by a bound in `copy`
 --> src/lib.rs:1:12
  |
1 | fn copy<R: Unpin, W>(_: R, _: W) {}
  |            ^^^^^ required by this bound in `copy`
help: consider restricting type parameter `T`
  |
3 | fn f<T: std::marker::Unpin>(r: T) {
  |       ++++++++++++++++++++

[hkmatsumoto]

Looks like a duplicate of #90101, but the MRE is nice and clean so we could use add it as a regression test.