Conversion to (DOMString or object) is broken

[Ms2ger]

pub enum StringOrObject {
    String(DOMString),
    Object(*mut JSObject),
}

impl ToJSValConvertible for StringOrObject {
    unsafe fn to_jsval(&self, cx: *mut JSContext, rval: MutableHandleValue) {
        match *self {
            StringOrObject::String(ref inner) => inner.to_jsval(cx, rval),
            StringOrObject::Object(ref inner) => inner.to_jsval(cx, rval),
        }
    }
}

impl FromJSValConvertible for StringOrObject {
    type Config = ();
    unsafe fn from_jsval(cx: *mut JSContext,
                         value: HandleValue,
                         _option: ())
                         -> Result<ConversionResult<StringOrObject>, ()> {
        if value.get().is_object() {

        }

        match StringOrObject::TryConvertToString(cx, value) {
            Err(_) => return Err(()),
            Ok(Some(value)) => return Ok(ConversionResult::Success(StringOrObject::String(value))),
            Ok(None) => (),
        }


        throw_not_in_union(cx, "Object");
        Err(())
    }
}

impl StringOrObject {
    unsafe fn TryConvertToString(cx: *mut JSContext, value: HandleValue) -> Result<Option<DOMString>, ()> {
        Ok(Some(match FromJSValConvertible::from_jsval(cx, value, StringificationBehavior::Default) {
            Ok(ConversionResult::Success(strval)) => strval,
            Ok(ConversionResult::Failure(error)) => {
                return Ok(None);
            }
            _ => { return Err(()); },
        }))
    }

    unsafe fn TryConvertToObject(cx: *mut JSContext, value: HandleValue) -> Result<Option<*mut JSObject>, ()> {
        Ok(Some(value.get().to_object()))
    }
}

We don't currently use the conversion in that direction, so this is not particularly urgent, but probably good to fix anyway.

[Xanewok]

Specific case of #17011.

[Xanewok]

This should be fixed by #20265.