in midst of refactor

orchid-api-derive/src/encode.rs

@@ -0,0 +1,68 @@
+
+use proc_macro::TokenStream;
+use proc_macro2 as pm2;
+use quote::ToTokens;
+use syn::spanned::Spanned;
+
+use crate::common::{add_trait_bounds, destructure, pos_field_name};
+
+pub fn derive(input: TokenStream) -> TokenStream {
+  // Parse the input tokens into a syntax tree
+  let input = parse_macro_input!(input as syn::DeriveInput);
+  let e_generics = add_trait_bounds(input.generics, parse_quote!(orchid_api_traits::Decode));
+  let (e_impl_generics, e_ty_generics, e_where_clause) = e_generics.split_for_impl();
+  let name = input.ident;
+  let encode = encode_body(&input.data);
+  let expanded = quote! {
+    impl #e_impl_generics orchid_api_traits::Encode for #name #e_ty_generics #e_where_clause {
+      fn encode<W: std::io::Write>(&self, write: &mut W) { #encode }
+    }
+  };
+  TokenStream::from(expanded)
+}
+
+fn encode_body(data: &syn::Data) -> Option<pm2::TokenStream> {
+  match data {
+    syn::Data::Union(_) => panic!("Unions can't be deserialized"),
+    syn::Data::Struct(str) => {
+      let dest = destructure(&str.fields)?;
+      let body = encode_items(&str.fields);
+      Some(quote! {
+        let Self #dest = &self;
+        #body
+      })
+    },
+    syn::Data::Enum(en) => {
+      let options = en.variants.iter().enumerate().map(|(i, v @ syn::Variant { ident, .. })| {
+        let dest = destructure(&v.fields).unwrap_or_default();
+        let body = encode_items(&v.fields);
+        quote! {
+          Self::#ident #dest => {
+            (#i as u64).encode(write);
+            #body
+          }
+        }
+      });
+      Some(quote! {
+        match self {
+          #(#options)*
+          _ => unreachable!("Autogenerated encode impl for all possible variants"),
+        }
+      })
+    },
+  }
+}
+
+fn encode_names<T: ToTokens>(names: impl Iterator<Item = T>) -> pm2::TokenStream {
+  quote! { #( #names .encode(write); )* }
+}
+
+fn encode_items(fields: &syn::Fields) -> Option<pm2::TokenStream> {
+  match fields {
+    syn::Fields::Unit => None,
+    syn::Fields::Named(_) => Some(encode_names(fields.iter().map(|f| f.ident.as_ref().unwrap()))),
+    syn::Fields::Unnamed(un) =>
+      Some(encode_names((0..fields.len()).map(|i| pos_field_name(i, un.span())))),
+  }
+}
+