From 2e3a5474501df3d1f6f0690f3c9c84f293734384 Mon Sep 17 00:00:00 2001
From: qm3ster <qm3ster@gmail.com>
Date: Sun, 10 May 2020 02:27:35 +0300
Subject: [PATCH] Enable deriving on generic types

---
 strong-xml-derive/src/lib.rs | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/strong-xml-derive/src/lib.rs b/strong-xml-derive/src/lib.rs
index 6d968d9..163d229 100644
--- a/strong-xml-derive/src/lib.rs
+++ b/strong-xml-derive/src/lib.rs
@@ -21,13 +21,25 @@ pub fn derive_xml_read(input: TokenStream) -> TokenStream {
 
     let input_lifetime = utils::gen_input_lifetime(&generics);
 
-    let mut generics_with_lifetime = generics.clone();
-    generics_with_lifetime.params.push(input_lifetime.into());
+    let mut generics_with_lifetime_and_where = generics.clone();
+    generics_with_lifetime_and_where
+        .params
+        .push(input_lifetime.into());
+    generics_with_lifetime_and_where
+        .make_where_clause()
+        .predicates
+        .extend(generics.type_params().map(|t| {
+            let x: syn::WherePredicate = syn::parse_quote! {#t: strong_xml::XmlRead<'__input>};
+            x
+        }));
+
+    let (_, ty_generics, _) = generics.split_for_impl();
+    let (impl_generics, _, where_clause) = generics_with_lifetime_and_where.split_for_impl();
 
     let impl_read = read::impl_read(Element::parse(input.clone()));
 
     let gen = quote! {
-        impl #generics_with_lifetime strong_xml::XmlRead<'__input> for #name #generics {
+        impl #impl_generics strong_xml::XmlRead<'__input> for #name #ty_generics #where_clause {
             fn from_reader(
                 mut reader: &mut strong_xml::XmlReader<'__input>
             ) -> strong_xml::XmlResult<Self> {
@@ -47,11 +59,22 @@ pub fn derive_xml_write(input: TokenStream) -> TokenStream {
 
     let name = &input.ident;
     let generics = &input.generics;
+    let mut generics_with_where = generics.clone();
+
+    generics_with_where
+        .make_where_clause()
+        .predicates
+        .extend(generics.type_params().map(|t| {
+            let x: syn::WherePredicate = syn::parse_quote! {#t: strong_xml::XmlWrite};
+            x
+        }));
+
+    let (impl_generics, ty_generics, where_clause) = generics_with_where.split_for_impl();
 
     let impl_write = write::impl_write(Element::parse(input.clone()));
 
     let gen = quote! {
-        impl #generics strong_xml::XmlWrite for #name #generics {
+        impl #impl_generics strong_xml::XmlWrite for #name #ty_generics #where_clause {
             fn to_writer<W: std::io::Write>(
                 &self,
                 mut writer: &mut strong_xml::XmlWriter<W>