error[E0636]: the feature `if_let` has already been enabled
  --> $DIR/duplicate-features.rs:7:12
   |
LL | #![feature(if_let)]
   |            ^^^^^^

error[E0636]: the feature `rust1` has already been enabled
  --> $DIR/duplicate-features.rs:4:12
   |
LL | #![feature(rust1)]
   |            ^^^^^

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0636`.