Suggest pin::pin! over Box::pin in diagnostics #109964
Description
Code
Consider the following code, taken from the async book (playground):
pub fn main() {
let mut test1 = Test::new("test1");
let mut test1 = unsafe { Pin::new_unchecked(&mut test1) };
Test::init(test1.as_mut());
let mut test2 = Test::new("test2");
let mut test2 = unsafe { Pin::new_unchecked(&mut test2) };
Test::init(test2.as_mut());
println!("a: {}, b: {}", Test::a(test1.as_ref()), Test::b(test1.as_ref()));
std::mem::swap(test1.get_mut(), test2.get_mut());
println!("a: {}, b: {}", Test::a(test2.as_ref()), Test::b(test2.as_ref()));
}Current output
error[E0277]: `PhantomPinned` cannot be unpinned
--> src/main.rs:47:26
|
47 | std::mem::swap(test1.get_mut(), test2.get_mut());
| ^^^^^^^ within `Test`, the trait `Unpin` is not implemented for `PhantomPinned`
|
= note: consider using `Box::pin`
note: required because it appears within the type `Test`Desired output
error[E0277]: `PhantomPinned` cannot be unpinned
--> src/main.rs:47:26
|
47 | std::mem::swap(test1.get_mut(), test2.get_mut());
| ^^^^^^^ within `Test`, the trait `Unpin` is not implemented for `PhantomPinned`
|
= note: consider using `core::pin::pin!`
note: required because it appears within the type `Test`Rationale and extra context
Local pin construction was stabilized in Rust 1.68. We should update the diagnostics to suggest this instead of the more expensive Box::pin call.
Other cases
No response
Anything else?
cc/ @wg-async
This is probably a "good first issue" as well. If someone can tag it as such?