Index: app/controllers/watchers_controller.rb
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- app/controllers/watchers_controller.rb	(revision dced4762005be491000490fc4c9661d0415272f7)
+++ app/controllers/watchers_controller.rb	(date 1540979006467)
@@ -93,6 +93,8 @@
       end
     elsif params[:project_id]
       @project = Project.visible.find_by_param(params[:project_id])
+    elsif params[:project_ids]
+      @projects = Project.visible.where(:identifier => params[:project_ids]).to_a
     end
   end
 
@@ -120,6 +122,9 @@
     scope = nil
     if params[:q].blank? && @project.present?
       scope = @project.users
+    elsif @projects.present?
+      user_ids = @projects.map { |p| p.users.map(&:id) }.flatten.uniq
+      scope = User.where(:id => user_ids)
     else
       scope = User.all.limit(100)
     end
Index: app/views/watchers/_new.html.erb
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- app/views/watchers/_new.html.erb	(revision dced4762005be491000490fc4c9661d0415272f7)
+++ app/views/watchers/_new.html.erb	(date 1540979062942)
@@ -12,13 +12,15 @@
     <% end  %>
   <% end %>
   <%= hidden_field_tag 'project_id', @project.id if @project %>
+  <%= hidden_field_tag 'project_ids', @projects if @projects %>
 
   <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.size == 1 ? watchables.first.id : nil),
-                 :project_id => @project) }')" %>
+                 :project_id => @project,
+                 :project_ids => @projects) }')" %>
 
   <div id="users_for_watcher">
     <%= principals_check_box_tags('watcher[user_ids][]', users) %>