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use crate::utils::{add_where_clauses_for_new_ident, SingleFieldData, State};
use proc_macro2::TokenStream;
use quote::{format_ident, quote};
use syn::{parse::Result, DeriveInput};
/// Provides the hook to expand `#[derive(Index)]` into an implementation of `Index`
pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
let index_type = format_ident!("__IdxT");
let mut state =
State::with_field_ignore(input, trait_name, trait_name.to_lowercase())?;
state.add_trait_path_type_param(quote! { #index_type });
let SingleFieldData {
field,
field_type,
input_type,
trait_path_with_params,
casted_trait,
member,
..
} = state.assert_single_enabled_field();
let type_where_clauses = quote! {
where #field_type: #trait_path_with_params
};
let new_generics = add_where_clauses_for_new_ident(
&input.generics,
&[field],
&index_type,
type_where_clauses,
true,
);
let (impl_generics, _, where_clause) = new_generics.split_for_impl();
let (_, ty_generics, _) = input.generics.split_for_impl();
Ok(quote! {
#[automatically_derived]
impl #impl_generics #trait_path_with_params for #input_type #ty_generics #where_clause {
type Output = #casted_trait::Output;
#[inline]
fn index(&self, idx: #index_type) -> &Self::Output {
#casted_trait::index(&#member, idx)
}
}
})
}