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//! Derive macros for justcode Encode and Decode traits.
use proc_macro::TokenStream;
use quote::quote;
use syn::{parse_macro_input, Data, DeriveInput, Fields};
/// Derive macro for the `Encode` trait.
#[proc_macro_derive(Encode)]
pub fn derive_encode(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let name = &input.ident;
let generics = &input.generics;
let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
let encode_body = match &input.data {
Data::Struct(data_struct) => match &data_struct.fields {
Fields::Named(fields) => {
let field_encodes = fields.named.iter().map(|field| {
let field_name = &field.ident;
quote! {
self.#field_name.encode(writer)?;
}
});
quote! {
#(#field_encodes)*
}
}
Fields::Unnamed(fields) => {
let field_encodes = fields.unnamed.iter().enumerate().map(|(i, _)| {
let index = syn::Index::from(i);
quote! {
self.#index.encode(writer)?;
}
});
quote! {
#(#field_encodes)*
}
}
Fields::Unit => {
quote! {}
}
},
Data::Enum(data_enum) => {
// Encode variant index first, then variant data
let variant_encodes = data_enum.variants.iter().enumerate().map(|(idx, variant)| {
let variant_idx = idx as u32;
let variant_name = &variant.ident;
match &variant.fields {
Fields::Named(fields) => {
let field_names: Vec<_> = fields.named.iter().map(|f| &f.ident).collect();
let field_encodes = field_names.iter().map(|field_name| {
quote! {
#field_name.encode(writer)?;
}
});
quote! {
#name::#variant_name { #(#field_names,)* } => {
use justcode_core::varint::encode_length;
encode_length(writer, #variant_idx as usize, writer.config())?;
#(#field_encodes)*
}
}
}
Fields::Unnamed(fields) => {
let field_count = fields.unnamed.len();
let field_indices: Vec<_> = (0..field_count)
.map(|i| syn::Index::from(i))
.collect();
let field_encodes = field_indices.iter().map(|index| {
quote! {
#index.encode(writer)?;
}
});
let field_patterns = field_indices.iter();
quote! {
#name::#variant_name(#(#field_patterns,)*) => {
use justcode_core::varint::encode_length;
encode_length(writer, #variant_idx as usize, writer.config())?;
#(#field_encodes)*
}
}
}
Fields::Unit => {
quote! {
#name::#variant_name => {
use justcode_core::varint::encode_length;
encode_length(writer, #variant_idx as usize, writer.config())?;
}
}
}
}
});
quote! {
match self {
#(#variant_encodes)*
}
}
}
Data::Union(_) => {
return syn::Error::new_spanned(
name,
"justcode does not support encoding unions",
)
.to_compile_error()
.into();
}
};
let expanded = quote! {
impl #impl_generics justcode_core::Encode for #name #ty_generics #where_clause {
fn encode(&self, writer: &mut justcode_core::writer::Writer) -> justcode_core::Result<()> {
#encode_body
Ok(())
}
}
};
TokenStream::from(expanded)
}
/// Derive macro for the `Decode` trait.
#[proc_macro_derive(Decode)]
pub fn derive_decode(input: TokenStream) -> TokenStream {
let input = parse_macro_input!(input as DeriveInput);
let name = &input.ident;
let generics = &input.generics;
let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
let decode_body = match &input.data {
Data::Struct(data_struct) => match &data_struct.fields {
Fields::Named(fields) => {
let field_decodes = fields.named.iter().map(|field| {
let field_name = &field.ident;
let field_ty = &field.ty;
quote! {
#field_name: <#field_ty as justcode_core::Decode>::decode(reader)?
}
});
quote! {
Ok(#name {
#(#field_decodes,)*
})
}
}
Fields::Unnamed(fields) => {
let field_decodes = fields.unnamed.iter().map(|field| {
let field_ty = &field.ty;
quote! {
<#field_ty as justcode_core::Decode>::decode(reader)?
}
});
quote! {
Ok(#name(#(#field_decodes,)*))
}
}
Fields::Unit => {
quote! {
Ok(#name)
}
}
},
Data::Enum(data_enum) => {
// Decode variant index first, then variant data
let variant_decodes = data_enum.variants.iter().enumerate().map(|(idx, variant)| {
let variant_idx = idx as u32;
let variant_name = &variant.ident;
match &variant.fields {
Fields::Named(fields) => {
let field_decodes = fields.named.iter().map(|field| {
let field_name = &field.ident;
let field_ty = &field.ty;
quote! {
#field_name: <#field_ty as justcode_core::Decode>::decode(reader)?
}
});
quote! {
#variant_idx => Ok(#name::#variant_name {
#(#field_decodes,)*
})
}
}
Fields::Unnamed(fields) => {
let field_decodes = fields.unnamed.iter().map(|field| {
let field_ty = &field.ty;
quote! {
<#field_ty as justcode_core::Decode>::decode(reader)?
}
});
quote! {
#variant_idx => Ok(#name::#variant_name(
#(#field_decodes,)*
))
}
}
Fields::Unit => {
quote! {
#variant_idx => Ok(#name::#variant_name)
}
}
}
});
quote! {
use justcode_core::varint::decode_length;
let variant_idx = decode_length(reader, reader.config())? as u32;
match variant_idx {
#(#variant_decodes,)*
_ => Err(justcode_core::error::JustcodeError::custom(format!("invalid variant index: {}", variant_idx))),
}
}
}
Data::Union(_) => {
return syn::Error::new_spanned(
name,
"justcode does not support decoding unions",
)
.to_compile_error()
.into();
}
};
let expanded = quote! {
impl #impl_generics justcode_core::Decode for #name #ty_generics #where_clause {
fn decode(reader: &mut justcode_core::reader::Reader) -> justcode_core::Result<Self> {
#decode_body
}
}
};
TokenStream::from(expanded)
}