hash32_derive/
lib.rs

1extern crate proc_macro;
2extern crate proc_macro2;
3#[macro_use]
4extern crate quote;
5#[macro_use]
6extern crate syn;
7
8use proc_macro::TokenStream;
9use proc_macro2::{TokenStream as TokenStream2, Literal as Literal2};
10use syn::{Data, DeriveInput, Fields, GenericParam, Generics};
11
12#[proc_macro_derive(Hash32)]
13pub fn derive_hash32(input: TokenStream) -> TokenStream {
14    let input: DeriveInput = syn::parse(input).unwrap();
15
16    let name = input.ident;
17    let generics = add_trait_bounds(input.generics);
18    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
19
20    let const_ = format_ident!("__IMPL_HASH32_FOR_{}", name);
21    let hash = compute_hash(&input.data);
22    quote!(
23        #[allow(non_upper_case_globals)]
24        const #const_: () = {
25            extern crate hash32;
26
27            impl #impl_generics hash32::Hash for #name #ty_generics #where_clause {
28                fn hash<H: hash32::Hasher>(&self, _h: &mut H) -> () {
29                    #hash
30                }
31             }
32        };
33    )
34    .into()
35}
36
37// Add a bound `T: Hash` to every type parameter T.
38fn add_trait_bounds(mut generics: Generics) -> Generics {
39    for param in &mut generics.params {
40        if let GenericParam::Type(ref mut type_param) = *param {
41            type_param.bounds.push(parse_quote!(hash32::Hash));
42        }
43    }
44    generics
45}
46
47fn compute_hash(data: &Data) -> TokenStream2 {
48    match *data {
49        Data::Struct(ref data) => match data.fields {
50            Fields::Named(ref fields) => {
51                let fnames = fields.named.iter().map(|f| &f.ident);
52                quote! {
53                    #(
54                        hash32::Hash::hash(&self.#fnames, _h);
55                    )*
56                }
57            }
58            Fields::Unnamed(ref fields) => {
59                let indices = (0..fields.unnamed.len()).map(|index| Literal2::usize_unsuffixed(index));
60                quote! {
61                    #(
62                        hash32::Hash::hash(&self.#indices, _h);
63                    )*
64                }
65            }
66            Fields::Unit => quote! {},
67        },
68        Data::Enum(..) | Data::Union(..) => {
69            panic!("#[derive(Hash)] doesn't currently support `enum` and `union`")
70        }
71    }
72}
hash32_derive/lib.rs

hash32_derive/
lib.rs
