error: can't mark as unstable using an already stable feature
  --> $DIR/unstable-attribute-rejects-already-stable-features.rs:6:1
   |
LL | #[unstable(feature = "arbitrary_enum_discriminant", issue = "42")]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this feature is already stable
LL | #[rustc_const_unstable(feature = "arbitrary_enum_discriminant", issue = "42")]
LL | const fn my_fun() {}
   | -------------------- the stability attribute annotates this item
   |
help: consider removing the attribute
  --> $DIR/unstable-attribute-rejects-already-stable-features.rs:6:1
   |
LL | #[unstable(feature = "arbitrary_enum_discriminant", issue = "42")]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: can't mark as unstable using an already stable feature
  --> $DIR/unstable-attribute-rejects-already-stable-features.rs:7:1
   |
LL | #[rustc_const_unstable(feature = "arbitrary_enum_discriminant", issue = "42")]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ this feature is already stable
LL | const fn my_fun() {}
   | -------------------- the stability attribute annotates this item
   |
help: consider removing the attribute
  --> $DIR/unstable-attribute-rejects-already-stable-features.rs:7:1
   |
LL | #[rustc_const_unstable(feature = "arbitrary_enum_discriminant", issue = "42")]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: aborting due to 2 previous errors