table & model changes for group managers with permission to edit membership

lib/guardian.rb

@@ -4,6 +4,7 @@ require_dependency 'guardian/post_guardian'
 require_dependency 'guardian/topic_guardian'
 require_dependency 'guardian/user_guardian'
 require_dependency 'guardian/post_revision_guardian'
+require_dependency 'guardian/group_guardian'
 
 # The guardian is responsible for confirming access to various site resources and operations
 class Guardian
@@ -13,6 +14,7 @@ class Guardian
   include TopicGuardian
   include UserGuardian
   include PostRevisionGuardian
+  include GroupGuardian
 
   class AnonymousUser
     def blank?; true; end

lib/guardian/group_guardian.rb

@@ -0,0 +1,11 @@
+#mixin for all guardian methods dealing with group permissions
+module GroupGuardian
+
+  # Edit authority for groups means membership changes only.
+  # Automatic groups are not represented in the GROUP_USERS
+  # table and thus do not allow membership changes.
+  def can_edit_group?(group)
+    (group.managers.include?(user) || is_admin?) && !group.automatic
+  end
+
+end