redmine/app/views/watchers/_new.html.erb

<%
title =
  if watchables.present?
    l(:"permission_add_#{watchables.first.class.name.underscore}_watchers")
  else
    l(:permission_add_issue_watchers)
  end
-%>
<h3 class="title"><%= title %></h3>

<%= form_tag(watchables.present? ? watchers_path : watchers_append_path,
             :remote => true,
             :method => :post,
             :id => 'new-watcher-form') do %>

  <% if watchables.present? %>
    <%= hidden_field_tag 'object_type', watchables.first.class.name.underscore %>
    <% watchables.each do |watchable| %>
      <%= hidden_field_tag 'object_id[]', watchable.id %>
    <% end  %>
  <% end %>
  <%= hidden_field_tag 'project_id', @project.id if @project %>

  <p><%= label_tag 'user_search', l(:label_user_search) %><%= text_field_tag 'user_search', nil %></p>
  <%= javascript_tag(
        "observeSearchfield(
          'user_search',
          'users_for_watcher',
          '#{escape_javascript(
               url_for(
                 :controller => 'watchers',
                 :action => 'autocomplete_for_user',
                 :object_type => (watchables.present? ? watchables.first.class.name.underscore : nil),
                 :object_id => (watchables.present? ? watchables.map(&:id) : nil),
                 :project_id => @project
               )
             )}'
         )"
       ) %>
  <div id="users_for_watcher">
    <%= principals_check_box_tags('watcher[user_ids][]', users) %>
  </div>

  <p class="buttons">
    <%= submit_tag l(:button_add), :name => nil, :onclick => "hideModal(this);" %>
    <%= link_to_function l(:button_cancel), "hideModal(this);" %>
  </p>
<% end %>