1 error[E0128]: generic parameters with a default cannot use forward declared identifiers
2 --> $DIR/generic-type-params-forward-mention.rs:2:23
4 LL | struct Foo<T = Option<U>, U = bool>(T, U);
5 | ^ defaulted generic parameters cannot be forward declared
7 error: aborting due to previous error
9 For more information about this error, try `rustc --explain E0128`.