error[E0658]: specialization is unstable
  --> $DIR/specialization-feature-gate-default.rs:7:1
   |
LL | / default impl<T> Foo for T {
LL | |     fn foo(&self) {}
LL | | }
   | |_^
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/31844
   = help: add #![feature(specialization)] to the crate attributes to enable

error: aborting due to previous error

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