error[E0658]: use of unstable library feature 'unstable_default'
  --> $DIR/generics-default-stability-where.rs:7:45
   |
LL | impl<T> Trait3<usize> for T where T: Trait2<usize> {
   |                                             ^^^^^
   |
   = help: add `#![feature(unstable_default)]` to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.