make attachments form openable by providing a local variable

By default, open the attachment for on the work package form

app/views/attachments/_nested_form.html.erb

@@ -39,11 +39,13 @@ an attachments_attributes= and not every model supports this we build a nested f
             end
 %>
 
-<fieldset id="attachments" class="header_collapsible collapsible collapsed">
+<% open ||= false %>
+
+<fieldset id="attachments" class="header_collapsible collapsible<%= open ? '' : ' collapsed' %>">
   <legend title="<%=l(:description_attachment_toggle)%>", onclick="toggleFieldset(this);">
     <a href="javascript:"><%=l(:label_attachment_plural)%></a>
   </legend>
-  <div style="display: none;">
+  <div <%= 'style="display: none;"' unless open %>>
     <div id="attachments_fields">
       <div class="grid-block" id="attachment_template">
         <div class="form--field">

app/views/work_packages/_form.html.erb

@@ -74,7 +74,7 @@ See doc/COPYRIGHT.rdoc for more details.
 <% if work_package.new_record? %>
   <hr class="form--separator -invisible">
 
-  <%= render :partial => 'attachments/nested_form' %>
+  <%= render :partial => 'attachments/nested_form', locals: { open: true } %>
 <% end %>
 
 <%= call_hook(:view_work_packages_form_details_bottom, { :issue => work_package, :form => f }) %>