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use crate::internal::get_root_path;
use proc_macro2::TokenStream;
use quote::{quote, quote_spanned, ToTokens};
use syn::{
parse::{Parse, ParseStream, Result as ParseResult},
parse_quote,
spanned::Spanned,
Data, DeriveInput, Fields, GenericParam, Generics, Ident, Path,
};
pub struct DeriveRead {
ident: Ident,
generics: Generics,
data: Data,
root_path: Path,
}
impl Parse for DeriveRead {
fn parse(input: ParseStream) -> ParseResult<Self> {
let DeriveInput {
attrs,
ident,
mut generics,
data,
..
} = input.parse()?;
let root_path = get_root_path(&attrs);
for param in &mut generics.params {
if let GenericParam::Type(ref mut type_param) = *param {
type_param.bounds.push(parse_quote!(#root_path::Read));
}
}
Ok(Self {
ident,
generics,
data,
root_path,
})
}
}
impl ToTokens for DeriveRead {
fn to_tokens(&self, tokens: &mut TokenStream) {
let name = &self.ident;
let (impl_generics, ty_generics, where_clause) =
&self.generics.split_for_impl();
let root = &self.root_path;
let call_site = ::proc_macro2::Span::call_site();
let reads = match &self.data {
Data::Struct(ref data) => match data.fields {
Fields::Named(ref fields) => {
let field_reads = fields.named.iter().map(|f| {
let ident = &f.ident;
let ty = &f.ty;
quote_spanned! {f.span() =>
let #ident = <#ty as #root::Read>::read(bytes, pos)?;
}
});
let field_names = fields.named.iter().map(|f| {
let ident = &f.ident;
quote! {
#ident,
}
});
quote! {
#(#field_reads)*
let item = #name {
#(#field_names)*
};
Ok(item)
}
}
Fields::Unnamed(ref fields) => {
let field_reads = fields.unnamed.iter().enumerate().map(|(i, f)| {
let ty = &f.ty;
let ident = Ident::new(format!("field_{}", i).as_str(), call_site);
quote_spanned! {f.span() =>
let #ident = <#ty as #root::Read>::read(bytes, pos)?;
}
});
let fields_list =
fields.unnamed.iter().enumerate().map(|(i, _f)| {
let ident = Ident::new(
format!("field_{}", i).as_str(),
call_site,
);
quote! {
#ident,
}
});
quote! {
#(#field_reads)*
let item = #name(
#(#fields_list)*
);
Ok(item)
}
}
Fields::Unit => {
unimplemented!();
}
},
Data::Enum(_) | Data::Union(_) => unimplemented!(),
};
let expanded = quote! {
#[automatically_derived]
#[allow(unused_qualifications)]
impl #impl_generics #root::Read for #name #ty_generics #where_clause {
#[inline]
fn read(bytes: &[u8], pos: &mut usize) -> Result<Self, #root::ReadError> {
#reads
}
}
};
expanded.to_tokens(tokens);
}
}