Shorthand projections inside RPITITs fail to resolve

[Vollbrecht]

Recent rust nigthly version can't compile previously working code, duo to compiler not being able to find associated type inside a "async fn in trait" definition.

Code

Compiling this code:

#![allow(async_fn_in_trait)]
pub trait foo {}

pub trait bar {
    type foo: foo;
}
pub trait baz {
    async fn boom<X: bar>() -> Result<(), X::foo>;
}

I expected to see this happen: In previous version up to nightly-2024-10-28 this code compiled

Instead, this happened: It stoped compiling with the error

error[E0220]: associated type `foo` not found for `X`
8 |     async fn boom<X: bar>() -> Result<(), X::foo>;
  |                                              ^^^ there is an associated type `foo` in the trait `bar`

Version it worked on

nightly-2024-10-28

Version with regression

nightly-2024-10-29

rustc --version --verbose:

rustc 1.84.0-nightly (1e4f10ba6 2024-10-29)
binary: rustc
commit-hash: 1e4f10ba6476e48a42a79b9f846a2d9366525b9e
commit-date: 2024-10-29
host: x86_64-unknown-linux-gnu
release: 1.84.0-nightly
LLVM version: 19.1.1

No, code just stops compiling.

[Dirbaio]

minimized it a bit more: playground

#![allow(async_fn_in_trait)]

pub trait Bar {
    type Foo;
}

pub trait Baz {
    async fn boom<X: Bar>() -> X::Foo;
}

bisected:

searched nightlies: from nightly-2024-10-28 to nightly-2024-10-30
regressed nightly: nightly-2024-10-30
searched commit range: 3f1be1e...1e4f10b
regressed commit: 2dece5b

Regression in rust-lang-ci@96aebe2
The PR introducing the regression in this rollup is #132194: Collect item bounds for RPITITs from trait where clauses ju…

[fmease]

cc @compiler-errors

[fmease]

Alt:

pub trait Bar {
    type Foo;
}

pub trait Baz {
    fn boom<X: Bar>() -> impl std::future::Future<Output = X::Foo>; //~ ERROR associated type `Foo` not found for `X`
}

[compiler-errors]

@rustbot claim