error: unsupported operation: unsized locals are not supported
  --> $DIR/unsized-local.rs:LL:CC
   |
LL |     let x = *(Box::new(A) as Box<dyn Foo>);
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ unsized locals are not supported
   |
   = help: this is likely not a bug in the program; it indicates that the program performed an operation that the interpreter does not support
   = note: BACKTRACE:
   = note: inside `main` at $DIR/unsized-local.rs:LL:CC

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to previous error