error[E0428]: the name `A` is defined multiple times --> $DIR/define-two.rs:15:21 | LL | #[proc_macro_derive(A)] | - previous definition of the macro `A` here ... LL | #[proc_macro_derive(A)] | ^ `A` redefined here | = note: `A` must be defined only once in the macro namespace of this module error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0428`.