error[E0004]: non-exhaustive patterns: `box _` not covered
  --> $DIR/issue-3601.rs:30:44
   |
LL |         box NodeKind::Element(ed) => match ed.kind {
   |                                            ^^^^^^^ pattern `box _` not covered
   |
note: `Box<ElementKind>` defined here
  --> $SRC_DIR/alloc/src/boxed.rs:LL:COL
   |
LL | / pub struct Box<
LL | |     T: ?Sized,
LL | |     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
LL | | >(Unique<T>, A);
   | |_^
   = note: the matched value is of type `Box<ElementKind>`
help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
   |
LL ~             box ElementKind::HTMLImageElement(ref d) if d.image.is_some() => { true }
LL +             box _ => todo!()
   |

error: aborting due to previous error

For more information about this error, try `rustc --explain E0004`.