Return only users who can see the watchable

app/views/work_packages/_form.html.erb

@@ -63,8 +63,8 @@ See doc/COPYRIGHT.rdoc for more details.
   <hr class="form_separator" />
   <div id="watchers_form">
     <label class="watcher_label"><%= l(:label_work_package_watchers) %></label>
-    <% work_package.project.users.sort.each do |user| -%>
-      <label class="floating"><%= check_box_tag 'work_package[watcher_user_ids][]', user.id, work_package.watched_by?(user) %> <%=h user %></label>
+    <% work_package.possible_watcher_users.sort.each do |user| -%>
+      <label class="floating"><%= check_box_tag 'work_package[watcher_user_ids][]', user.id, work_package.watched_by?(user) && work_package.visible?(user) %> <%=h user %></label>
     <% end -%>
   </div>
 <% end %>

lib/plugins/acts_as_watchable/lib/acts_as_watchable.rb

@@ -89,10 +89,10 @@ module Redmine
           # TODO: There might be addable users which are not in the current
           #       project. But its hard (performance wise) to find them
           #       correctly. So we only search for users in the project scope.
-          #       Also, the watchable might not be allowed to be seen by all
-          #       users in the project.
           #       This implementation is so wrong, it makes me sad.
-          project.users
+          watchers = project.users
+          watchers = watchers.select { |w| visible?(w) } if respond_to?(:visible?)
+          watchers
         end
 
         # Returns an array of users that are proposed as watchers