Error code E0698

When using generators (or async) all type variables must be bound so a generator can be constructed.

Erroneous code example:

#![allow(unused)]
fn main() {
async fn bar<T>() -> () {}

async fn foo() {
    bar().await; // error: cannot infer type for `T`
}
}

In the above example T is unknowable by the compiler. To fix this you must bind T to a concrete type such as String so that a generator can then be constructed:

#![allow(unused)]
fn main() {
async fn bar<T>() -> () {}

async fn foo() {
    bar::<String>().await;
    //   ^^^^^^^^ specify type explicitly
}
}