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use crate::utils::{add_extra_where_clauses, SingleFieldData, State};
use proc_macro2::TokenStream;
use quote::quote;
use syn::{parse::Result, DeriveInput};
/// Provides the hook to expand `#[derive(DerefMut)]` into an implementation of `DerefMut`
pub fn expand(input: &DeriveInput, trait_name: &'static str) -> Result<TokenStream> {
let state =
State::with_field_ignore_and_forward(input, trait_name, "deref_mut".into())?;
let SingleFieldData {
input_type,
trait_path,
casted_trait,
ty_generics,
field_type,
member,
info,
..
} = state.assert_single_enabled_field();
let (body, generics) = if info.forward {
(
quote! { #casted_trait::deref_mut(&mut #member) },
add_extra_where_clauses(
&input.generics,
quote! {
where #field_type: #trait_path
},
),
)
} else {
(quote! { &mut #member }, input.generics.clone())
};
let (impl_generics, _, where_clause) = generics.split_for_impl();
Ok(quote! {
#[automatically_derived]
impl #impl_generics #trait_path for #input_type #ty_generics #where_clause {
#[inline]
fn deref_mut(&mut self) -> &mut Self::Target {
#body
}
}
})
}