error: `diagnostic::on_unimplemented` is not an unsafe attribute
  --> $DIR/unsafe-safe-attribute_diagnostic.rs:1:3
   |
LL | #[unsafe(diagnostic::on_unimplemented(
   |   ^^^^^^ this is not an unsafe attribute
   |
   = note: extraneous unsafe is not allowed in attributes

error: aborting due to 1 previous error