Confusing error when using CoercePointee #134846
Description
Code
#![feature(derive_coerce_pointee)] use std::marker::CoercePointee; use std::rc::Rc; #[repr(transparent)] #[derive(CoercePointee)] struct RcWithId<T: ?Sized> { inner: Rc<(i32, Box<T>)>, }Current output
error[E0277]: the trait bound `Box<T>: Unsize<Box<__S>>` is not satisfied --> src/main.rs:6:10 | 6 | #[derive(CoercePointee)] | ^^^^^^^^^^^^^ the trait `Unsize<Box<__S>>` is not implemented for `Box<T>` | = note: all implementations of `Unsize` are provided automatically by the compiler, see <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> for more information = note: required for `Rc<(i32, Box<T>)>` to implement `DispatchFromDyn<Rc<(i32, Box<__S>)>>` = note: this error originates in the derive macro `CoercePointee` (in Nightly builds, run with -Z macro-backtrace for more info) error[E0277]: the trait bound `Box<T>: Unsize<Box<__S>>` is not satisfied --> src/main.rs:6:10 | 6 | #[derive(CoercePointee)] | ^^^^^^^^^^^^^ the trait `Unsize<Box<__S>>` is not implemented for `Box<T>` | = note: all implementations of `Unsize` are provided automatically by the compiler, see <https://doc.rust-lang.org/stable/std/marker/trait.Unsize.html> for more information = note: this error originates in the derive macro `CoercePointee` (in Nightly builds, run with -Z macro-backtrace for more info)Desired output
Something that does not mention internal things like `Unsize` or `__S`Rationale and extra context
No response
Other cases
Rust Version
current nightlyAnything else?
No response