ilyagr.bsky.social
just playing with tangled
rfc1149.tngl.sh
1mod content_hash;
2
3extern crate proc_macro;
4
5use quote::quote;
6use syn::parse_macro_input;
7use syn::DeriveInput;
8
9/// Derive macro generating an impl of the trait `ContentHash`.
10///
11/// Derives the `ContentHash` trait for a struct by calling `ContentHash::hash`
12/// on each of the struct members in the order that they're declared. All
13/// members of the struct must implement the `ContentHash` trait.
14#[proc_macro_derive(ContentHash)]
15pub fn derive_content_hash(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
16 let input = parse_macro_input!(input as DeriveInput);
17
18 // The name of the struct.
19 let name = &input.ident;
20
21 // Generate an expression to hash each of the fields in the struct.
22 let hash_impl = content_hash::generate_hash_impl(&input.data);
23
24 // Handle structs and enums with generics.
25 let generics = content_hash::add_trait_bounds(input.generics);
26 let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
27
28 let expanded = quote! {
29 #[automatically_derived]
30 impl #impl_generics ::jj_lib::content_hash::ContentHash for #name #ty_generics
31 #where_clause {
32 fn hash(&self, state: &mut impl digest::Update) {
33 #hash_impl
34 }
35 }
36 };
37 expanded.into()
38}