Updating the contents of an image?

I've been a bit confused today about the Image widget. I want to have it display the contents of a file on disk and if that file changes display the updated version. But I could not figure out how to make image actually update itself once Data changes. I had a look at the implementation and realised that the update method is not implemented. It also didn't seem to work with a LensWrap.

I wrapped it in a controller and this works, but I was wondering whether this isn't quite the stumbling block for new users.

struct ImageController;

impl druid::widget::Controller<WatchoutState, Image> for ImageController {
    fn update(
        &mut self,
        child: &mut Image,
        ctx: &mut druid::UpdateCtx,
        old_data: &WatchoutState,
        data: &WatchoutState,
        env: &druid::Env,
    ) {
        child.set_image_data(data.image.clone())
        ctx.children_changed();
    }
}

// Usage
let image = Image::new(ImageBuf::empty());
let size_box = druid::widget::SizedBox::new(image.controller(ImageController))
        .expand()

Is there a reason why images don't update? (or am I holding it wrong?) Otherwise I'd gladly submit a PR.

Start with the Image widget implementation, especially its update method, and compare it with the controller's update entry point shown here. Reproduce the file-backed image case from the linked watchout example, including the LensWrap behavior, then verify that changing the image data refreshes the displayed image without the controller workaround.