This would be very helpful to add new features from plugins related to custom fields.

Thanks a lot to take in accout this very small patch

  <% unless @issue_custom_fields.empty? %>
  
<%= toggle_checkboxes_link('#project_issue_custom_fields input[type=checkbox]:enabled') %><%=l(:label_custom_field_plural)%>
  <% @issue_custom_fields.each do |custom_field| %>
    
      <%= check_box_tag 'project[issue_custom_field_ids][]', custom_field.id, (@project.all_issue_custom_fields.include? custom_field),
          :disabled => (custom_field.is_for_all? ? "disabled" : nil),
          :id => nil %>
      <%= custom_field_name_tag(custom_field) %>
    
  <% end %>
  <%= hidden_field_tag 'project[issue_custom_field_ids][]', '' %>
  

<%
  # The new hook
-%>
<%= call_hook(:view_project_settings_issues_custom_fields, { :issue_custom_fields => @issue_custom_fields, :project => @project }) %>
  <% end %>