(codegen) Improve generics support for impl_object macro

Author: theduke

integration_tests/juniper_tests/src/codegen/impl_object.rs

@@ -11,6 +11,7 @@ struct Context {
     version: Option<String>,
 }
 
+
 #[derive(Default)]
 struct TheQuery {
     b: bool,

juniper_codegen/src/impl_object.rs

@@ -168,6 +168,7 @@ pub fn build(args: TokenStream, body: TokenStream) -> TokenStream {
         scalar: impl_attrs.scalar,
         description: impl_attrs.description,
         fields: Vec::new(),
+        generics: _impl.generics.clone(),
     };
 
     for item in &mut _impl.items {
@@ -274,7 +275,7 @@ pub fn build(args: TokenStream, body: TokenStream) -> TokenStream {
         }
     }
 
-    let graphql_type_impl = definition.to_tokens();
+    let graphql_type_impl = definition.into_tokens();
     let body = quote!(
         #_impl
         #graphql_type_impl

juniper_codegen/src/util.rs

@@ -273,10 +273,11 @@ pub struct GraphQLTypeDefiniton {
     pub scalar: Option<syn::Type>,
     pub description: Option<String>,
     pub fields: Vec<GraphQLTypeDefinitionField>,
+    pub generics: syn::Generics,
 }
 
 impl GraphQLTypeDefiniton {
-    pub fn to_tokens(&self) -> proc_macro2::TokenStream {
+    pub fn into_tokens(self) -> proc_macro2::TokenStream {
         let name = &self.name;
         let ty = &self._type;
         let context = self
@@ -347,8 +348,36 @@ impl GraphQLTypeDefiniton {
             None => quote!(),
         };
 
+
+        let (_, ty_generics, _) = self.generics.split_for_impl();
+
+        let mut generics = self.generics.clone();
+
+        if self.scalar.is_none() {
+            generics.params.push(parse_quote!(__S));
+            {
+                let where_clause = generics.where_clause.get_or_insert(parse_quote!(where));
+                where_clause
+                    .predicates
+                    .push(parse_quote!(__S: juniper::ScalarValue));
+                where_clause
+                    .predicates
+                    .push(parse_quote!(for<'__b> &'__b __S: juniper::ScalarRefValue<'__b>));
+            }
+        }
+
+        let scalar = self
+            .scalar
+            .as_ref()
+            .map(|s| quote!( #s ))
+            .unwrap_or_else(|| quote!( __S ));
+
+        let (impl_generics, _, where_clause) = generics.split_for_impl();
+
         quote!(
-            impl juniper::GraphQLType<#scalar> for #ty {
+        impl#impl_generics juniper::GraphQLType<#scalar> for #ty #ty_generics
+            #where_clause
+        {
                 type Context = #context;
                 type TypeInfo = ();
 
@@ -361,7 +390,7 @@ impl GraphQLTypeDefiniton {
                     registry: &mut juniper::Registry<'r, #scalar>
                 ) -> juniper::meta::MetaType<'r, #scalar>
                     where #scalar : 'r,
-                        for<'z> &'z juniper::DefaultScalarValue: juniper::ScalarRefValue<'z>,
+                        // for<'z> &'z juniper::DefaultScalarValue: juniper::ScalarRefValue<'z>,
                 {
                     let fields = vec![
                         #( #field_definitions ),*
@@ -377,9 +406,9 @@ impl GraphQLTypeDefiniton {
                     &self,
                     _info: &(),
                     field: &str,
-                    args: &juniper::Arguments,
-                    executor: &juniper::Executor<Self::Context>,
-                ) -> juniper::ExecutionResult {
+                    args: &juniper::Arguments<#scalar>,
+                    executor: &juniper::Executor<Self::Context, #scalar>,
+                ) -> juniper::ExecutionResult<#scalar> {
                     match field {
                         #( #resolve_matches )*
                         _ => {