error[E0658]: cannot cast `dyn A` to `dyn B`, trait upcasting coercion is experimental
  --> $DIR/upcast-through-struct-tail.rs:10:5
   |
LL |     x
   |     ^
   |
   = note: see issue #65991 <https://github.com/rust-lang/rust/issues/65991> for more information
   = help: add `#![feature(trait_upcasting)]` to the crate attributes to enable
   = note: required when coercing `Box<Wrapper<(dyn A + 'a)>>` into `Box<Wrapper<(dyn B + 'a)>>`

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0658`.