error: malformed `rustc_on_unimplemented` attribute input --> $DIR/issue-104140.rs:5:1 | LL | #[rustc_on_unimplemented] | ^^^^^^^^^^^^^^^^^^^^^^^^^ | help: the following are the possible correct uses | LL | #[rustc_on_unimplemented = "message"] | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ LL | #[rustc_on_unimplemented(/*opt*/ message = "...", /*opt*/ label = "...", /*opt*/ note = "...")] | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: aborting due to 1 previous error