type alias `Plus2` is never used about rust HOT 10 OPEN

There are also similar older versions of this issue, like the following (playground). That's been warning since 1.57:

use std::mem;

#[repr(transparent)]
pub struct X<T: ?Sized> {
    pub inner: T,
}

pub struct Y {}

impl Drop for Y {
    fn drop(&mut self) {
        type A = Vec<u8>;
        const _: () = assert!(mem::size_of::<X<A>>() == mem::size_of::<A>());
    }
}

Note that this is not a reduction of the OP and not necessarily a duplicate, but was encountered in real world code.

from rust.

warnings are popping up as well, so wrong repo I guess ? is there a way to transfer this issue to rustc ?

from rust.

No worries, somebody will chase it down at some point :)

from rust.

Regression in rust-lang-ci@4cfe57a
The PR introducing the regression in this rollup is #122382: Detect unused structs which implement private traits

I will have a look

from rust.

dead_code comes from rustc, does cargo +nightly-2024-07-18 check --all-targets --features serde exhibit the same behaviour?

from rust.

checking

from rust.

This will need a smaller reproduction. Any chance you could try extracting the relevant code out?

from rust.

I don't really have time currently I'm afraid :/ otherwise I could offer an automated bisect on that

from rust.

@rustbot claim

from rust.

Reduced (play):

struct T<X>(X);

type A<X> = T<X>;

trait Tr {
    fn foo();
}

impl<X> Tr for T<A<X>> {
    fn foo() {}
}

fn main() {
   T::<T<()>>::foo();
}

from rust.