System Initiative

use darling::FromAttributes; use manyhow::{ Result, bail, }; use proc_macro::TokenStream; use proc_macro2::TokenStream as TokenStream2; use quote::quote; use syn::{ Data, DataStruct, DeriveInput, Ident, }; #[derive(Debug, FromAttributes)] #[darling(attributes(acceptable))] struct Config { version: u64, } pub(crate) fn expand(input: TokenStream, errors: &mut manyhow::Emitter) -> Result<TokenStream2> { let input = syn::parse::<DeriveInput>(input)?; let DeriveInput { ident, data, attrs, .. } = input; let config = Config::from_attributes(&attrs)?; match data { Data::Struct(data_struct) => derive_from_struct(ident, data_struct, config, errors), Data::Enum(_) | Data::Union(_) => { bail!("current only struct types are supported for `#[derive(Versioned)]`") } } } fn derive_from_struct( ident: Ident, data: DataStruct, config: Config, _errors: &mut manyhow::Emitter, ) -> Result<TokenStream2> { let version = config.version; let Some(id_field) = data .fields .iter() .filter_map(|field| field.ident.as_ref()) .find(|ident| *ident == "id") else { bail!(ident, "unable to find 'id' field in struct"); }; Ok(quote! { impl acceptable::Versioned for #ident { #[inline] fn id(&self) -> acceptable::RequestId { self.#id_field.into() } #[inline] fn message_version() -> u64 { #version } } }) }