cannot implement async trait that returning "impl Trait" #281
Description
Since rust 1.75, we are able to write functions that return impl Trait in trait.
I'd like to use it with async_trait, like below:
#[async_trait::async_trait]
pub trait X {
type Error;
async fn x(&self) -> Result<impl AsRef<str> + Send + Sync, Self::Error>;
}The code upon can pass the compilation, but implementing X cannot.
struct T;
#[async_trait::async_trait]
impl X for T {
type Error = ();
async fn x(&self) -> Result<impl AsRef<str> + Send + Sync, Self::Error> {
Ok("Hello World")
}
}Complation error:
error[E0562]: `impl Trait` is not allowed in paths
--> scratch/src/main.rs:11:33
|
11 | async fn x(&self) -> Result<impl AsRef<str> + Send + Sync, Self::Error> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
error[E0562]: `impl Trait` is not allowed in the type of variable bindings
--> scratch/src/main.rs:11:33
|
11 | async fn x(&self) -> Result<impl AsRef<str> + Send + Sync, Self::Error> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `impl Trait` is only allowed in arguments and return types of functions and methods
After inspecting code generated by async_trait macro:
impl X for T {
type Error = ();
#[allow(
elided_named_lifetimes,
clippy::async_yields_async,
clippy::diverging_sub_expression,
clippy::let_unit_value,
clippy::needless_arbitrary_self_type,
clippy::no_effect_underscore_binding,
clippy::shadow_same,
clippy::type_complexity,
clippy::type_repetition_in_bounds,
clippy::used_underscore_binding
)]
fn x<'life0, 'async_trait>(
&'life0 self,
) -> ::core::pin::Pin<
Box<
dyn ::core::future::Future<
Output = Result<impl AsRef<str>, Self::Error>,
> + ::core::marker::Send + 'async_trait,
>,
>
where
'life0: 'async_trait,
Self: 'async_trait,
{
Box::pin(async move {
if let ::core::option::Option::Some(__ret) = ::core::option::Option::None::<
Result<impl AsRef<str> + Send + Sync, Self::Error>,
> {
#[allow(unreachable_code)] return __ret;
}
let __self = self;
let __ret: Result<impl AsRef<str> + Send + Sync, Self::Error> = { Ok("Hello World") };
#[allow(unreachable_code)] __ret
})
}
}Upon inspecting the generated code by the async_trait macro, the impl Trait appears in type annotations, causing the issue. Replacing these occurrences of impl Trait with _ resolves the compilation errors.
Can the macro automatically replace all instances of impl Trait with _ to bypass this issue?