Submit image when selected

This could have been done with a tiny amount of inline JS, but I went this way in case I needed any special logic for UJS. It turns out we don't.. but it still looks a bit cleaner this way.

app/views/admin/products_v3/_edit_image.html.haml

@@ -5,12 +5,11 @@
 
   -# Submit to controller, because StimulusReflex doesn't support file uploads
   = form_for [:admin, product, image], url: admin_product_image_path(product, image),
-      html: { multipart: true } do |f|
+      html: { multipart: true }, data: { controller: "form" } do |f|
     %input{ type: :hidden, name: :return_url, value: return_url}
     = f.hidden_field :viewable_id, value: product.id
 
     %p
       -# label.button provides a handy shortcut to open the file selector on click. Unfortunately this trick isn't keyboard accessible though..
       = f.label :attachment, t(".upload"), class: "button primary icon-upload-alt"
-      = f.file_field :attachment, style: "display: none"
-      = f.submit # todo: submit automatically
+      = f.file_field :attachment, style: "display: none", "data-action": "change->form#submit"

app/webpacker/controllers/form_controller.js

@@ -0,0 +1,7 @@
+import { Controller } from "stimulus";
+
+export default class FormController extends Controller {
+  submit() {
+    this.element.submit();
+  }
+}