error: Undefined Behavior: constructing invalid value: wrong trait in wide pointer vtable: expected `Trait fn(&'a ())>`, but encountered `Trait` --> tests/fail/validity/dyn-transmute-inner-binder.rs:LL:CC | LL | let y: &dyn Trait fn(&'a ())> = unsafe { std::mem::transmute(x) }; | ^^^^^^^^^^^^^^^^^^^^^^ Undefined Behavior occurred here | = help: this indicates a bug in the program: it performed an invalid operation, and caused Undefined Behavior = help: see https://doc.rust-lang.org/nightly/reference/behavior-considered-undefined.html for further information = note: BACKTRACE: = note: inside `main` at tests/fail/validity/dyn-transmute-inner-binder.rs:LL:CC note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace error: aborting due to 1 previous error