Make #[derive(JSTraceable)] a procedural macro

components/jstraceable_derive/lib.rs

@@ -0,0 +1,58 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#![feature(proc_macro, proc_macro_lib)]
+
+extern crate proc_macro;
+#[macro_use] extern crate quote;
+extern crate syn;
+extern crate synstructure;
+
+#[cfg(not(test))]
+#[proc_macro_derive(JSTraceable)]
+pub fn expand_token_stream(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
+    expand_string(&input.to_string()).parse().unwrap()
+}
+
+fn expand_string(input: &str) -> String {
+    let mut type_ = syn::parse_macro_input(input).unwrap();
+
+    let style = synstructure::BindStyle::Ref.into();
+    let match_body = synstructure::each_field(&mut type_, &style, |binding| {
+        Some(quote! { #binding.trace(tracer); })
+    });
+
+    let name = &type_.ident;
+    let (impl_generics, ty_generics, mut where_clause) = type_.generics.split_for_impl();
+    for param in &type_.generics.ty_params {
+        where_clause.predicates.push(syn::WherePredicate::BoundPredicate(syn::WhereBoundPredicate {
+            bound_lifetimes: Vec::new(),
+            bounded_ty: syn::Ty::Path(None, param.ident.clone().into()),
+            bounds: vec![syn::TyParamBound::Trait(
+                syn::PolyTraitRef {
+                    bound_lifetimes: Vec::new(),
+                    trait_ref: syn::parse_path("::dom::bindings::trace::JSTraceable").unwrap(),
+                },
+                syn::TraitBoundModifier::None
+            )],
+        }))
+    }
+
+    let tokens = quote! {
+        #type_
+
+        impl #impl_generics ::dom::bindings::trace::JSTraceable for #name #ty_generics #where_clause {
+            #[inline]
+            #[allow(unused_variables, unused_imports)]
+            fn trace(&self, tracer: *mut ::js::jsapi::JSTracer) {
+                use ::dom::bindings::trace::JSTraceable;
+                match *self {
+                    #match_body
+                }
+            }
+        }
+    };
+
+    tokens.to_string()
+}