[E0403] False positive generated for implicit future type

[hchataing]

Code

pub async fn test() {
    let a = async { loop { } };
    let a = std::pin::pin!(a);
    
    use std::future::Future;
    use std::pin::Pin;
    use std::task::{Poll, Context};
    
    #[allow(non_camel_case_types)]
    struct Foo<'a, a> {
        a: Pin<&'a mut a>,
    }
    
    #[allow(non_camel_case_types)]
    impl<'a, a: Future<Output = ()>> Future for Foo<'a, a> {
        type Output = ();
        fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
            self.a.as_mut().poll(cx)
        }
    }
    
    Foo { a }.await
}

Current output

Compiling playground v0.0.1 (/playground)
error[E0403]: the name `a` is already used for a generic parameter in this item's generic parameters
  --> src/lib.rs:11:20
   |
3  |     let a = async { loop { } };
   |         - first use of `a`
...
11 |     struct Foo<'a, a> {
   |                    ^ already used

error[E0403]: the name `a` is already used for a generic parameter in this item's generic parameters
  --> src/lib.rs:16:14
   |
3  |     let a = async { loop { } };
   |         - first use of `a`
...
16 |     impl<'a, a: Future<Output = ()>> Future for Foo<'a, a> {
   |              ^ already used

error[E0277]: `Foo<'_, _>` is not a future
  --> src/lib.rs:23:15
   |
23 |     Foo { a }.await
   |              -^^^^^
   |              ||
   |              |`Foo<'_, _>` is not a future
   |              help: remove the `.await`
   |
   = help: the trait `Future` is not implemented for `Foo<'_, _>`, which is required by `Foo<'_, _>: IntoFuture`
   = note: Foo<'_, _> must be a future or must implement `IntoFuture` to be awaited
   = note: required for `Foo<'_, _>` to implement `IntoFuture`

Some errors have detailed explanations: E0277, E0403.
For more information about an error, try `rustc --explain E0277`.
error: could not compile `playground` (lib) due to 3 previous errors

Desired output

No error code raised

Rationale and extra context

This code snippet uses neither of the two error code conditions presented in https://doc.rust-lang.org/error_codes/E0403.html.
It seems that the variable name a for the assignment let a = async { loop { test::a().await; } }; is used implicitly in the type name, which would cause the struct declaration to shadow the first declaration.

Other cases

No response

Rust Version

Nightly channel
Build using the Nightly version: 1.82.0-nightly
(2024-08-18 6de928dce9472b864f4e)

Anything else?

No response

[compiler-errors]

Oof -- I think I caused this regression in #128357.

[compiler-errors]

Minimal:

pub fn foo() {
    let a = 1;
    struct Foo<a> { a: a, };
}

[hchataing]

That was fast :) thank you for your help