error[E0275]: overflow evaluating the requirement `Element: MetaSized`
  --> $DIR/overflow.rs:16:16
   |
LL | struct Element(<Box<Box<Element>> as ParseTokens>::Output);
   |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: required for `Box<Element>` to implement `ParseTokens`
  --> $DIR/overflow.rs:12:31
   |
LL | impl<T: ParseTokens + ?Sized> ParseTokens for Box<T> {
   |      -                        ^^^^^^^^^^^     ^^^^^^
   |      |
   |      unsatisfied trait bound introduced here
   = note: 1 redundant requirement hidden
   = note: required for `Box<Box<Element>>` to implement `ParseTokens`

error[E0275]: overflow evaluating the requirement `Box<Element>: ParseTokens`
  --> $DIR/overflow.rs:18:22
   |
LL | impl ParseTokens for Element {
   |                      ^^^^^^^
   |
note: required for `Box<Box<Element>>` to implement `ParseTokens`
  --> $DIR/overflow.rs:12:31
   |
LL | impl<T: ParseTokens + ?Sized> ParseTokens for Box<T> {
   |         -----------           ^^^^^^^^^^^     ^^^^^^
   |         |
   |         unsatisfied trait bound introduced here
note: required because it appears within the type `Element`
  --> $DIR/overflow.rs:16:8
   |
LL | struct Element(<Box<Box<Element>> as ParseTokens>::Output);
   |        ^^^^^^^
note: required by a bound in `ParseTokens`
  --> $DIR/overflow.rs:9:1
   |
LL | / trait ParseTokens {
LL | |     type Output;
LL | | }
   | |_^ required by this bound in `ParseTokens`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0275`.