This is the error message I've got when compiling the code from Chapter 19 macros: error: the `#[proc_macro_derive]` attribute is only usable with crates of the `proc-macro` crate type Have no idea how to fix this.
Using #![feature(proc_macro)] in combination with attributes enabled by #[proc_macro_derive(MyTrait, attributes(mycrate))] (e.g. #[mycrate(some_option = "something")]) fails to compile on the current nightly with error: macro undefined: ...