Making trait method `async` causes inference failure (E0790)

[benschulz]

I tried this code (playground):

struct Frob;

trait FromFrob: Sized {
    async fn from_frob(frob: &Frob) -> Self;
}

struct Frobbable;
impl FromFrob for Frobbable {
    async fn from_frob(_frob: &Frob) -> Self {
        todo!()
    }
}

fn main() {
    futures::executor::block_on(async move {
        let _: Frobbable = FromFrob::from_frob(&Frob).await;
    });
}

I expected to see this happen: Compilation succeeds as for the synchronous version (playground).

Instead, this happened: Compilation failed with the following error.

error[E0790]: cannot call associated function on trait without specifying the corresponding `impl` type
  --> src/main.rs:16:28
   |
4  |     async fn from_frob(frob: &Frob) -> Self;
   |     ---------------------------------------- `FromFrob::from_frob` defined here
...
16 |         let _: Frobbable = FromFrob::from_frob(&Frob).await;
   |                            ^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot call associated function of trait
   |
help: use the fully-qualified path to the only available implementation
   |
16 |         let _: Frobbable = <Frobbable as FromFrob>::from_frob(&Frob).await;
   |                            +++++++++++++         +

Meta

rustc --version --verbose:

rustc 1.89.0-nightly (414482f6a 2025-05-13)
binary: rustc
commit-hash: 414482f6a0d4e7290f614300581a0b55442552a3
commit-date: 2025-05-13
host: x86_64-unknown-linux-gnu
release: 1.89.0-nightly
LLVM version: 20.1.4

I also tried RUSTFLAGS="-Znext-solver=globally" which had no impact.

Potentially relates to #135698.