From 8241e6c656495448c61007ac19c41376924d6773 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lena=20Hellstr=C3=B6m?= <lena@stygian.nexus>
Date: Mon, 20 Sep 2021 15:58:16 +0200
Subject: [PATCH] Add generic bound support to derive

---
 derive/src/derive_struct.rs | 23 +++++++++++++++++------
 derive/src/lib.rs           |  6 ++++--
 tests/derive.rs             |  6 ++++--
 3 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/derive/src/derive_struct.rs b/derive/src/derive_struct.rs
index 7f922e9..1668657 100644
--- a/derive/src/derive_struct.rs
+++ b/derive/src/derive_struct.rs
@@ -1,15 +1,16 @@
 use crate::Result;
 use proc_macro::TokenStream;
-use quote::quote;
-use syn::{spanned::Spanned, Ident};
+use quote::{quote, quote_spanned};
+use syn::{spanned::Spanned, Generics, Ident};
 
 pub struct DeriveStruct {
     name: Ident,
+    generics: Generics,
     fields: Vec<Ident>,
 }
 
 impl DeriveStruct {
-    pub fn parse(name: Ident, str: syn::DataStruct) -> Result<Self> {
+    pub fn parse(name: Ident, generics: Generics, str: syn::DataStruct) -> Result<Self> {
         let fields = match str.fields {
             syn::Fields::Named(fields) => fields
                 .named
@@ -24,11 +25,21 @@ impl DeriveStruct {
                 .collect(),
             syn::Fields::Unit => Vec::new(),
         };
-        Ok(Self { name, fields })
+        Ok(Self {
+            name,
+            generics,
+            fields,
+        })
     }
 
     pub fn to_encodable(self) -> Result<TokenStream> {
-        let DeriveStruct { name, fields } = self;
+        let DeriveStruct {
+            name,
+            generics,
+            fields,
+        } = self;
+
+        let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
 
         let fields = fields
             .into_iter()
@@ -40,7 +51,7 @@ impl DeriveStruct {
             .collect::<Vec<_>>();
 
         let result = quote! {
-            impl bincode::enc::Encodeable for #name {
+            impl #impl_generics bincode::enc::Encodeable for #name #ty_generics #where_clause {
                 fn encode<E: bincode::enc::Encode>(&self, mut encoder: E) -> Result<(), bincode::error::EncodeError> {
                     #(#fields)*
                     Ok(())
diff --git a/derive/src/lib.rs b/derive/src/lib.rs
index 82be10a..c9cce74 100644
--- a/derive/src/lib.rs
+++ b/derive/src/lib.rs
@@ -21,7 +21,8 @@ pub fn derive_encodable(input: TokenStream) -> TokenStream {
 fn derive_encodable_inner(input: DeriveInput) -> Result<TokenStream> {
     match input.data {
         syn::Data::Struct(struct_definition) => {
-            DeriveStruct::parse(input.ident, struct_definition).and_then(|str| str.to_encodable())
+            DeriveStruct::parse(input.ident, input.generics, struct_definition)
+                .and_then(|str| str.to_encodable())
         }
         syn::Data::Enum(enum_definition) => {
             DeriveEnum::parse(input.ident, enum_definition).and_then(|str| str.to_encodable())
@@ -39,7 +40,8 @@ pub fn derive_decodable(input: TokenStream) -> TokenStream {
 fn derive_decodable_inner(input: DeriveInput) -> Result<TokenStream> {
     match input.data {
         syn::Data::Struct(struct_definition) => {
-            DeriveStruct::parse(input.ident, struct_definition).and_then(|str| str.to_decodable())
+            DeriveStruct::parse(input.ident, input.generics, struct_definition)
+                .and_then(|str| str.to_decodable())
         }
         syn::Data::Enum(enum_definition) => {
             DeriveEnum::parse(input.ident, enum_definition).and_then(|str| str.to_decodable())
diff --git a/tests/derive.rs b/tests/derive.rs
index 4aa0156..155925b 100644
--- a/tests/derive.rs
+++ b/tests/derive.rs
@@ -1,6 +1,8 @@
+use bincode::enc::Encodeable;
+
 #[derive(bincode::Encodable, PartialEq, Debug)]
-pub struct Test {
-    a: i32,
+pub struct Test<T: Encodeable> {
+    a: T,
     b: u32,
     c: u8,
 }