Auto merge of #8412 - ecoal95:webidl-sequence-return, r=jdm

Add WebIDL sequence return values

And use it for `WebGLRenderingContext::getSupportedExtensions`.
Part of #544

<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/8412)
<!-- Reviewable:end -->

1 files changed, 23 insertions, 0 deletions

diff --git a/components/script/dom/bindings/conversions.rs b/components/script/dom/bindings/conversions.rs
index 45279e7a966..493ed4c0c27 100644
--- a/components/script/dom/bindings/conversions.rs
+++ b/components/script/dom/bindings/conversions.rs
@@ -46,6 +46,7 @@ use js::jsapi::{HandleId, HandleObject, HandleValue, JS_GetClass};
 use js::jsapi::{JSClass, JSContext, JSObject, JSString, MutableHandleValue};
 use js::jsapi::{JS_GetLatin1StringCharsAndLength, JS_GetReservedSlot};
 use js::jsapi::{JS_GetTwoByteStringCharsAndLength, JS_NewStringCopyN};
+use js::jsapi::{JS_NewArrayObject1, JS_DefineElement, RootedValue, RootedObject};
 use js::jsapi::{JS_NewUCStringCopyN, JS_StringHasLatin1Chars, JS_WrapValue};
 use js::jsval::{BooleanValue, Int32Value, NullValue, UInt32Value, UndefinedValue};
 use js::jsval::{JSVal, ObjectOrNullValue, ObjectValue, StringValue};
@@ -811,6 +812,28 @@ impl<T: FromJSValConvertible> FromJSValConvertible for Option<T> {
     }
 }
 
+impl<T: ToJSValConvertible> ToJSValConvertible for Vec<T> {
+    fn to_jsval(&self, cx: *mut JSContext, rval: MutableHandleValue) {
+        let js_array = RootedObject::new(cx,
+                                         unsafe { JS_NewArrayObject1(cx, self.len() as libc::size_t) });
+        assert!(!js_array.handle().is_null());
+
+        for (index, obj) in self.iter().enumerate() {
+            let mut val = RootedValue::new(cx, UndefinedValue());
+            obj.to_jsval(cx, val.handle_mut());
+
+            unsafe {
+                assert!(JS_DefineElement(cx, js_array.handle(),
+                                         index as u32, val.handle(), js::JSPROP_ENUMERATE, None, None));
+            }
+        }
+
+        unsafe {
+            rval.set(ObjectValue(&*js_array.handle().get()));
+        }
+    }
+}
+
 //http://heycam.github.io/webidl/#es-object
 impl ToJSValConvertible for *mut JSObject {
     fn to_jsval(&self, cx: *mut JSContext, rval: MutableHandleValue) {