revert collapsed file forms in edit mode, this caused too much trouble. Added some comments concerning that.

app/assets/javascripts/exercises.js

@@ -12,6 +12,9 @@ $(function() {
     $('#files li:last select[name*="file_type_id"]').val(getSelectedExecutionEnvironment().file_type_id);
     $('#files li:last select').chosen(window.CodeOcean.CHOSEN_OPTIONS);
     $('body, html').scrollTo('#add-file');
+    // if we collapse the file forms by default, we need to click on the new element in order to open it.
+    // however, this crashes for more files (if we add several ones by clicking the add button more often), since the elements are probably not correctly added to the files list.
+    //$('#files li:last>div:first>a>div').click();
   };
 
   var ajaxError = function() {

app/views/exercises/_file_form.html.slim

@@ -4,7 +4,7 @@ li.panel.panel-default
     a.file-heading data-toggle="collapse" data-parent="#files" href="#collapse#{id}"
       div.clearfix role="button"
         span = f.object.name
-  .panel-collapse.collapse id="collapse#{id}" role="tabpanel"
+  .panel-collapse.collapse-in id="collapse#{id}" role="tabpanel"
     .panel-body
       .clearfix = link_to(t('shared.destroy'), '#', class:'btn btn-warning btn-sm discard-file pull-right')
       .form-group