RPITIT seems to assume return type is the type parameter when it looks the same

[Artemis21]

I tried this code:

#![feature(return_position_impl_trait_in_trait)]

trait Foo<T> {
    fn foo<F2: Foo<T>>(self) -> impl Foo<T>;
}

struct Bar;

impl Foo<u8> for Bar {
    fn foo<F2: Foo<u8>>(self) -> impl Foo<u8> {
        self
    }
}

fn main() {}

I expected this to compile without error, since it is implementing the trait correctly.

Instead, the following error was shown:

error[E0053]: method `foo` has an incompatible type for trait
  --> src/main.rs:10:42
   |
10 |     fn foo<F2: Foo<u8>>(self, f2: F2) -> impl Foo<u8> {
   |            --                            ^^^^^^^^^^^^
   |            |                             |
   |            |                             expected `u8`, found type parameter `F2`
   |            this type parameter           help: change the output type to match the trait: `impl Foo<u8>`
   |
note: type in trait
  --> src/main.rs:4:41
   |
4  |     fn foo<F2: Foo<T>>(self, f2: F2) -> impl Foo<T>;
   |                                         ^^^^^^^^^^^
   = note: expected fn pointer `fn(Bar, _) -> impl Foo<u8>`
              found fn pointer `fn(Bar, _) -> impl Foo<u8>`

It suggests replacing the code with the code I already have, which doesn't make much sense, as well as complaining that two things which appear identical are not.

Playground.

Meta

rustc --version --verbose:

rustc 1.66.0-nightly (3f83906b3 2022-09-24)
binary: rustc
commit-hash: 3f83906b30798bf61513fa340524cebf6676f9db
commit-date: 2022-09-24
host: x86_64-unknown-linux-gnu
release: 1.66.0-nightly
LLVM version: 15.0.0

[Rageking8]

@rustbot label +T-compiler +requires-nightly +F-return_position_impl_trait_in_trait +D-invalid-suggestion

[compiler-errors]

@rustbot claim