我正在编写我的第一个 proc 宏,尽管尝试通读此错误、structopt 和 derived_more 的源代码,但我似乎无法准确找到我正在寻找的内容。我想改变这个:
#[derive(Attach)]
#[attach(foo(SomeType, OtherType))]
#[attach(bar(OtherType))]
struct Plugin {}
进入这个:
impl Attach for Plugin {
fn attach(self, srv: &mut Server) {
let this = Arc::new(self);
srv.foo_order(this.clone(), &[TypeId::of::<SomeType>(), TypeId::of::<OtherType>()]);
srv.bar_order(this, &[TypeId::of::<OtherType>()]);
}
}
我已经开始编写一个 proc 宏,但在尝试解析属性时遇到了麻烦:
extern crate proc_macro;
use proc_macro::{Span, TokenStream};
use quote::quote;
use std::any::TypeId;
use syn::{
parse::ParseStream, parse_macro_input, Attribute, AttributeArgs, DeriveInput, Ident, Result,
};
#[proc_macro_derive(Attach, attributes(attach))]
pub fn register_macro(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
impl_register(input)
}
fn impl_register(input: DeriveInput) -> TokenStream {
let name = &input.ident;
let attrs = &input.attrs;
for attr in attrs {
if attr.path.is_ident("attach") {
parse_attach_attribute(&attr);
}
}
println!("{:#?}", input);
TokenStream::from(quote! {
impl ::corten::Attach for #name {
fn attach(self, srv: &mut ::corten::Server) {
}
}
})
}
fn parse_attach_attribute(attr: &Attribute) -> Result<Dependency> {
let list: syn::MetaList = attr.parse_args()?;
// println!("{:#?}", list);
let ident = list.path.get_ident().expect("expected identifier");
let method = Ident::new(&format!("{}_order", ident), ident.span());
println!("{:#?}", method);
let dependencies = list
.nested
.into_pairs()
.map(|pair| pair.into_value())
.collect::<Vec<_>>();
// How does one get the identifiers out of a NestedMeta?
println!("{:#?}", dependencies);
// attr.parse_args_with(|input: ParseStream| {
// let ident = input.p
// let method = Ident::new(&format!("{}_order", ident), Span::call_site());
// let dep = Dependency {
// method,
// }
// })
unimplemented!()
}
struct Dependency {
method: Ident,
dependencies: Vec<Ident>,
}
我遇到的困难是如何将属性列表实际变成可用的形式?据我所知,我需要从中解析“foo”和“bar”,&[Attribute]
以便构建方法标识符,以及“SomeType”和“OtherType”标识符,我最终都会将它们输入quote!
. TokenStream
如果我在控制台中打印,所有信息都在那里:
[
Attribute {
pound_token: Pound,
style: Outer,
bracket_token: Bracket,
path: Path {
leading_colon: None,
segments: [
PathSegment {
ident: Ident {
ident: "attach",
span: #0 bytes(103..109),
},
arguments: None,
},
],
},
tokens: TokenStream [
Group {
delimiter: Parenthesis,
stream: TokenStream [
Ident {
ident: "predecode",
span: #0 bytes(110..119),
},
Group {
delimiter: Parenthesis,
stream: TokenStream [
Ident {
ident: "SomeType",
span: #0 bytes(120..128),
},
Punct {
ch: ',',
spacing: Alone,
span: #0 bytes(128..129),
},
Ident {
ident: "OtherType",
span: #0 bytes(130..139),
},
],
span: #0 bytes(119..140),
},
],
span: #0 bytes(109..141),
},
],
},
Attribute {
pound_token: Pound,
style: Outer,
bracket_token: Bracket,
path: Path {
leading_colon: None,
segments: [
PathSegment {
ident: Ident {
ident: "attach",
span: #0 bytes(145..151),
},
arguments: None,
},
],
},
tokens: TokenStream [
Group {
delimiter: Parenthesis,
stream: TokenStream [
Ident {
ident: "preresolve",
span: #0 bytes(152..162),
},
Group {
delimiter: Parenthesis,
stream: TokenStream [
Ident {
ident: "OtherType",
span: #0 bytes(163..172),
},
],
span: #0 bytes(162..173),
},
],
span: #0 bytes(151..174),
},
],
},
]
但我没有办法真正做到这一点。我怎么去tokens[0].stream.ident
?