hanger/
lib.rs

1extern crate proc_macro;
2
3#[macro_use]
4extern crate quote;
5
6use proc_macro::TokenStream;
7use syn::parse;
8use syn::punctuated::Punctuated;
9
10#[proc_macro_attribute]
11pub fn hook(attr: TokenStream, input: TokenStream) -> TokenStream {
12    let hooks = syn::parse_macro_input!(attr as Hooks);
13    let mut function = syn::parse_macro_input!(input as syn::ItemFn);
14
15    let before: Box<syn::Block> = if let Some(func) = hooks.before {
16        Box::new(syn::parse_quote!({ #func() }))
17    } else {
18        Box::new(syn::parse_quote!({}))
19    };
20    let after: Box<syn::Block> = if let Some(func) = hooks.after {
21        Box::new(syn::parse_quote!({ #func() }))
22    } else {
23        Box::new(syn::parse_quote!({}))
24    };
25
26    let body = function.block;
27    function.block = Box::new(syn::parse_quote!({
28        #before { #body } #after
29    }));
30    TokenStream::from(quote!(#function))
31}
32
33struct Hooks {
34    before: Option<syn::TypePath>,
35    after: Option<syn::TypePath>,
36}
37
38mod pk {
39    use super::*;
40
41    syn::custom_keyword!(before);
42    syn::custom_keyword!(after);
43
44    pub enum Arg {
45        Before {
46            b: before,
47            eq: syn::Token![=],
48            func: syn::TypePath,
49        },
50        After {
51            a: after,
52            eq: syn::Token![=],
53            func: syn::TypePath,
54        },
55    }
56
57    impl parse::Parse for Arg {
58        fn parse(input: parse::ParseStream) -> parse::Result<Self> {
59            let lookahead = input.lookahead1();
60            if lookahead.peek(before) {
61                Ok(Arg::Before {
62                    b: input.parse::<before>()?,
63                    eq: input.parse::<syn::Token![=]>()?,
64                    func: input.parse()?,
65                })
66            } else {
67                Ok(Arg::After {
68                    a: input.parse::<after>()?,
69                    eq: input.parse::<syn::Token![=]>()?,
70                    func: input.parse()?,
71                })
72            }
73        }
74    }
75}
76
77impl parse::Parse for Hooks {
78    fn parse(input: parse::ParseStream) -> parse::Result<Self> {
79        let mut hb = None;
80        let mut ha = None;
81        let parser = Punctuated::<pk::Arg, syn::Token![,]>::parse_terminated;
82        if let Ok(args) = parser(input) {
83            for arg in args.iter() {
84                match arg {
85                    pk::Arg::After { func, .. } => ha = Some(func.clone()),
86                    pk::Arg::Before { func, .. } => hb = Some(func.clone()),
87                }
88            }
89        }
90
91        if hb.is_none() && ha.is_none() {
92            hb = Some(input.parse::<syn::TypePath>()?);
93        }
94
95        Ok(Hooks {
96            after: ha,
97            before: hb,
98        })
99    }
100}
hanger/lib.rs

hanger/
lib.rs
