Derive DomObject with a proc macro

components/domobject_derive/lib.rs

@@ -0,0 +1,53 @@
+/* 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/. */
+
+extern crate proc_macro;
+#[macro_use] extern crate quote;
+extern crate syn;
+
+#[proc_macro_derive(DomObject)]
+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 type_ = syn::parse_macro_input(input).unwrap();
+
+    let first_field_name = if let syn::Body::Struct(syn::VariantData::Struct(ref fields)) = type_.body {
+        let first_field = fields.first().expect("#[derive(DomObject)] should not be applied on empty structs");
+        first_field.ident.as_ref().unwrap()
+    } else {
+        panic!("#[derive(DomObject)] should only be applied on proper structs")
+    };
+
+    let name = &type_.ident;
+    let (impl_generics, ty_generics, where_clause) = type_.generics.split_for_impl();
+
+    let tokens = quote! {
+        impl #impl_generics ::js::conversions::ToJSValConvertible for #name #ty_generics #where_clause {
+            #[allow(unsafe_code)]
+            unsafe fn to_jsval(&self,
+                                cx: *mut ::js::jsapi::JSContext,
+                                rval: ::js::jsapi::MutableHandleValue) {
+                let object = ::dom::bindings::reflector::DomObject::reflector(self).get_jsobject();
+                object.to_jsval(cx, rval)
+            }
+        }
+
+        impl #impl_generics ::dom::bindings::reflector::DomObject for #name #ty_generics #where_clause {
+            #[inline]
+            fn reflector(&self) -> &::dom::bindings::reflector::Reflector {
+                self.#first_field_name.reflector()
+            }
+        }
+
+        impl #impl_generics ::dom::bindings::reflector::MutDomObject for #name #ty_generics #where_clause {
+            fn init_reflector(&mut self, obj: *mut ::js::jsapi::JSObject) {
+                self.#first_field_name.init_reflector(obj);
+            }
+        }
+    };
+
+    tokens.to_string()
+}