|  | error: unstable feature `feat_foo` is used without being enabled. | 
|  | --> $DIR/unstable-impl-cannot-use-feature.rs:26:5 | 
|  | | | 
|  | LL |     Bar::foo(); | 
|  | |     ^^^ | 
|  | | | 
|  | = help: The feature can be enabled by marking the current item with `#[unstable_feature_bound(feat_foo)]` | 
|  | note: required for `Bar` to implement `Foo` | 
|  | --> $DIR/unstable-impl-cannot-use-feature.rs:20:6 | 
|  | | | 
|  | LL | #[unstable_feature_bound(feat_foo)] | 
|  | | ----------------------------------- unsatisfied trait bound introduced here | 
|  | LL | impl Foo for Bar { | 
|  | |      ^^^     ^^^ | 
|  |  | 
|  | error: aborting due to 1 previous error | 
|  |  |