#[derive(Debug)] fails when used with a raw pointer to DST

[whitequark]

... with the following error message:

error[E0277]: the trait bound `core::ops::Fn() -> bool + 'static: core::marker::Sized` is not satisfied
   --> /home/whitequark/Work/artiq-dev/artiq/artiq/runtime/../runtime.rs/src/sched.rs:109:16
    |
109 |     Completion(*const (Fn() -> bool + 'static)),
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
/home/whitequark/Work/artiq-dev/artiq/artiq/runtime/../runtime.rs/src/sched.rs:107:10: 107:15 note: in this expansion of #[derive(Debug)] (defined in /home/whitequark/Work/artiq-dev/artiq/artiq/runtime/../runtime.rs/src/sched.rs)
    |
    = note: `core::ops::Fn() -> bool + 'static` does not have a constant size known at compile-time
    = note: required because of the requirements on the impl of `core::fmt::Debug` for `*const core::ops::Fn() -> bool + 'static`
    = note: required because of the requirements on the impl of `core::fmt::Debug` for `&*const core::ops::Fn() -> bool + 'static`
    = note: required for the cast to the object type `core::fmt::Debug`

since the Debug impl for raw pointers just prints the actual pointer, I don't see why it should require the pointee to be Sized.

[apasel422]

Do you have a code snippet that exhibits this?

[apasel422]

Seems like this is a duplicate of #30427.

[whitequark]

trait T {}
#[derive(Debug)]
struct S(*const T);

[durka]

I'm working on this.

[durka]

It is not a duplicate of #30427. That was fixed by #31479 which extended the Pointer implementation to unsized T. However, the Debug impl, which merely delegates to Pointer, was not updated in that PR.

[whitequark]

Thanks @durka