impl_trait_in_fn_trait_return breaks with ref params

[douglas-raillard-arm]

I tried the new impl_trait_in_fn_trait_return feature tracked at #99697

#![feature(impl_trait_in_fn_trait_return)]

// Having the closure take any kind of reference as parameter results in a
// compilation error. Turning "&()" into "()" fixes it.

fn allowed_in_ret_type() -> impl Fn(&()) -> impl Into<u32> {
    |_| 0u32
}

// This compiles just fine:
// fn allowed_in_ret_type() -> impl Fn(()) -> impl Into<u32> {
//     |_| 0u32
// }

I expected to see this happen:

The code should compile.

Instead, this happened:

error: concrete type differs from previous defining opaque type use
--> src/main.rs:4:9
    |
4 |     |_| 0u32
    |         ^^^^ expected `impl Into<u32>`, got `u32`
    |
note: previous use here
    --> src/main.rs:4:5
    |
4 |     |_| 0u32
    |     ^^^^^^^^

    error[E0720]: cannot resolve opaque type
    --> src/main.rs:3:45
    |
3 | fn allowed_in_ret_type() -> impl Fn(&()) -> impl Into<u32> {
    |                                             ^^^^^^^^^^^^^^ recursive opaque type
        4 |     |_| 0u32
        |     -------- returning here with type `[closure@src/main.rs:4:5: 4:8]`

        For more information about this error, try `rustc --explain E0720`.

Meta

rustc --version --verbose:

rustc 1.67.0-nightly (edf018221 2022-11-02)

[Rageking8]

@rustbot label +T-compiler +F-impl_trait_in_fn_trait_return +requires-nightly