error[E0658]: associated type defaults are unstable
  --> $DIR/feature-gate-assoc-type-defaults.rs:4:5
   |
LL |     type Bar = u8;
   |     ^^^^^^^^^^^^^^
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/29661
   = help: add `#![feature(associated_type_defaults)]` to the crate attributes to enable

error: aborting due to previous error

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