审题

// This test looks for a derive macro with the right name to exist. For now the
// test doesn't require any specific code to be generated by the macro, so
// returning an empty TokenStream should be sufficient.
//
// Before moving on, have your derive macro parse the macro input as a
// syn::DeriveInput syntax tree.
//
//
// Resources:
//
//   - The DeriveInput syntax tree which represents input of a derive macro:
//     https://docs.rs/syn/1.0/syn/struct.DeriveInput.html
//
//   - An example of a derive macro implemented using Syn:
//     https://github.com/dtolnay/syn/tree/master/examples/heapsize

use derive_debug::CustomDebug;

#[derive(CustomDebug)]
pub struct Field {
    name: &'static str,
    bitmask: u16,
}

fn main() {}

从这一关的测试用例不难发现，解题方式不过也是一个占位，相当于是热身。

题解

详细可以参看builder-1，这里直接粘贴代码。

#[proc_macro_derive(CustomDebug, attributes(debug))]
pub fn derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let ast = syn::parse_macro_input!(input as syn::DeriveInput);
    match solution1(&ast) {
        syn::Result::Ok(token_stream) => {
            return proc_macro::TokenStream::from(token_stream);
        }
        syn::Result::Err(e) => {
            return e.into_compile_error().into();
        }
    }
}

当然，代码里面直接Result::Ok(proc-macro2:: TokenStream::new())即可，因为当前的确不需要做任何的事情。

整体

#[proc_macro_derive(CustomDebug, attributes(debug))]
pub fn derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let ast = syn::parse_macro_input!(input as syn::DeriveInput);
    match solution1(&ast) {
        syn::Result::Ok(token_stream) => {
            return proc_macro::TokenStream::from(token_stream);
        }
        syn::Result::Err(e) => {
            return e.into_compile_error().into();
        }
    }
}

要用以前的分步习惯，我们之后还是把常用的方法抽取到common.rs，其他每个问题的回答抽取到对应的solutionx.rs中

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