error[E0277]: the size for values of type `[u8]` cannot be known at compilation time
  --> $DIR/wf-array-elem-sized.rs:7:10
   |
LL |     foo: [[u8]],
   |          ^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `[u8]`
   = note: slice and array elements must have `Sized` type

error: aborting due to previous error

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