How to do it...

1. Create a new sub-crate for the custom derive with cargo new chapter-five-derive.

2. Open the newly generated chapter-five-derive/Cargo.toml.
3. Add this directly above the [dependencies] section of the file in order to mark the crate as a procedural macro crate:

[lib]
proc-macro = true

4. Under [dependencies], add the following lines:

syn = "0.11.11"
quote = "0.3.15"

If you want, you can go to the crates.io web pages for syn (https://crates.io/crates/syn) and quote (https://crates.io/crates/quote) to check for the newest version and use that one instead.

5.  In the chapter-five-derive/src/lib.rs file, delete the generated code and add the following:

1    extern crate proc_macro; 
2    #[macro_use]
3    extern crate quote;
4    extern crate syn;
5 
6    use proc_macro::TokenStream;
7 
8    // HelloWorld is the name for the derive
9    // hello_world_name is the name of our optional attribute
10   #[proc_macro_derive(HelloWorld, attributes(hello_world_name...