"Parameter type may not live long enough" compilation error for async-fn-in-trait

[bryangarza]

Encountered in these test cases:

• async-generics.rs
• async-generics-and-bounds.rs
• async-lifetimes-and-bounds.rs

From #102642

Here is async-generics.rs

// edition: 2021

#![feature(async_fn_in_trait)]
#![allow(incomplete_features)]

trait MyTrait<T, U> {
    async fn foo(&self) -> &(T, U);
}
//~^^ ERROR the parameter type `U` may not live long enough
//~| ERROR the parameter type `T` may not live long enough

impl<T, U> MyTrait<T, U> for (T, U) {
    async fn foo(&self) -> &(T, U) {
        self
    }
}

fn main() {}

I expected to see this happen: Successful compilation

Instead, this happened:

error[E0311]: the parameter type `U` may not live long enough
  --> $DIR/async-generics.rs:7:28
   |
LL |     async fn foo(&self) -> &(T, U);
   |                            ^^^^^^^
   |
note: the parameter type `U` must be valid for the anonymous lifetime as defined here...
  --> $DIR/async-generics.rs:7:18
   |
LL |     async fn foo(&self) -> &(T, U);
   |                  ^
note: ...so that the reference type `&(T, U)` does not outlive the data it points at
  --> $DIR/async-generics.rs:7:28
   |
LL |     async fn foo(&self) -> &(T, U);
   |                            ^^^^^^^

error[E0311]: the parameter type `T` may not live long enough
  --> $DIR/async-generics.rs:7:28
   |
LL |     async fn foo(&self) -> &(T, U);
   |                            ^^^^^^^
   |
note: the parameter type `T` must be valid for the anonymous lifetime as defined here...
  --> $DIR/async-generics.rs:7:18
   |
LL |     async fn foo(&self) -> &(T, U);
   |                  ^
note: ...so that the reference type `&(T, U)` does not outlive the data it points at
  --> $DIR/async-generics.rs:7:28
   |
LL |     async fn foo(&self) -> &(T, U);
   |                            ^^^^^^^

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0311`.

Meta

rustc --version --verbose:

rustc 1.66.0-nightly (092255976 2022-10-03)
binary: rustc
commit-hash: 092255976862c1f0121bb4446acd38336a860c4f
commit-date: 2022-10-03
host: x86_64-unknown-linux-gnu
release: 1.66.0-nightly
LLVM version: 15.0.2

[compiler-errors]

This is probably actually the same issue as the other one, and as #102552 (comment).

[bryangarza]

Ah, so #102681 and 102552#issuecomment are all the same? Okay, I'm going to use this one as the master one and link it in all 4 tests.

[compiler-errors]

Yeah, please don't remove the tests but I don't actually know if all of these outlives errors are valid errors or not... best to just lump them into one issue for now.

[compiler-errors]

Thanks, and sorry for the confusion.

[bryangarza]

Gotcha, yeah I'll keep all of the tests in the PR! :)