1 use crate::utils::{add_where_clauses_for_new_ident, SingleFieldData, State};
2 use proc_macro2::{Span, TokenStream};
3 use quote::quote;
4 use syn::{parse::Result, DeriveInput, Ident};
5
6 /// Provides the hook to expand `#[derive(Index)]` into an implementation of `Index`
expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream>7 pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
8 let index_type = &Ident::new("__IdxT", Span::call_site());
9 let mut state = State::with_field_ignore(
10 input,
11 trait_name,
12 quote!(::core::ops),
13 trait_name.to_lowercase(),
14 )?;
15 state.add_trait_path_type_param(quote!(#index_type));
16 let SingleFieldData {
17 field,
18 field_type,
19 input_type,
20 trait_path_with_params,
21 casted_trait,
22 member,
23 ..
24 } = state.assert_single_enabled_field();
25
26 let type_where_clauses = quote! {
27 where #field_type: #trait_path_with_params
28 };
29
30 let new_generics = add_where_clauses_for_new_ident(
31 &input.generics,
32 &[field],
33 index_type,
34 type_where_clauses,
35 true,
36 );
37
38 let (impl_generics, _, where_clause) = new_generics.split_for_impl();
39 let (_, ty_generics, _) = input.generics.split_for_impl();
40 Ok(quote! {
41 impl#impl_generics #trait_path_with_params for #input_type#ty_generics #where_clause
42 {
43 type Output = #casted_trait::Output;
44 #[inline]
45 fn index(&self, idx: #index_type) -> &Self::Output {
46 #casted_trait::index(&#member, idx)
47 }
48 }
49 })
50 }
51