error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
  --> $DIR/wf-impl-self-type.rs:5:14
   |
LL | impl Foo for Option<[u8]> {}
   |              ^^^^^^^^^^^^ doesn't have a size known at compile-time
   | 
  ::: $SRC_DIR/core/src/option.rs:LL:COL
   |
LL | pub enum Option<T> {
   |                 - required by this bound in `std::option::Option`
   |
   = help: the trait `std::marker::Sized` is not implemented for `[u8]`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.