Unable to call `Self` in blanket implementation

[sommd]

I think this is a bug, sorry if it's not.

Problem

When creating a blanket impl, e.g. impl<T: A> B for T, if you trying to call a fn on Self it doesn't work:

use async_trait::async_trait;

#[async_trait]
trait A {
    async fn a();
}

trait B {
    fn b();
}

#[async_trait]
impl<T: B> A for T {
    async fn a() {
        Self::b();
    }
}

error[E0276]: impl has stricter requirements than trait
  --> src/lib.rs:12:1
   |
5  |     async fn a();
   |     ------------- definition of `a` from trait
...
12 | #[async_trait]
   | ^^^^^^^^^^^^^^ impl has extra requirement `T: 'async_trait`
   |
   = note: this error originates in the attribute macro `async_trait` (in Nightly builds, run with -Z macro-backtrace for more info)

Same problem even if B has #[async_trait] (with or without B::b() being async).

Expected

I feel like this should work because it works when not using async:

trait A {
    fn a();
}

trait B {
    fn b();
}

impl<T: B> A for T {
    fn a() {
        Self::b();
    }
}

Workaround

I did figure out a workaround (halfway through writing this 😅), which is to use T instead of Self, so I don't think this issue is high priority, but I figured I should still report it (and share the workaround).

use async_trait::async_trait;

#[async_trait]
trait A {
    async fn a();
}

trait B {
    fn b();
}

#[async_trait]
impl<T: B> A for T {
    async fn a() {
        T::b();
    }
}