| error[E0128]: type parameters with a default cannot use forward declared identifiers | |
| --> $DIR/generic-type-params-forward-mention.rs:12:23 | |
| | | |
| LL | struct Foo<T = Option<U>, U = bool>(T, U); | |
| | ^ defaulted type parameters cannot be forward declared | |
| error: aborting due to previous error | |
| For more information about this error, try `rustc --explain E0128`. |