fix ldap group link and add some debug info

app/models/ldap_group_link.rb

@@ -2,6 +2,8 @@ class LdapGroupLink < ActiveRecord::Base
   include Gitlab::Access
   belongs_to :group
 
+  NIL_ATTRIBUTES = %w[cn filter].freeze
+
   validates :cn, :group_access, :group_id, presence: true, unless: :filter
   validates :cn, uniqueness: { scope: [:group_id, :provider] }, unless: :filter
   validates :filter, :group_access, :group_id, presence: true, unless: :cn
@@ -12,6 +14,8 @@ class LdapGroupLink < ActiveRecord::Base
 
   scope :with_provider, ->(provider) { where(provider: provider) }
 
+  before_save :update_blank_attributes
+
   def access_field
     group_access
   end
@@ -30,4 +34,10 @@ class LdapGroupLink < ActiveRecord::Base
   def provider_label
     config.label
   end
+
+  private
+
+  def update_blank_attributes
+    NIL_ATTRIBUTES.each { |attr| self[attr] = nil if self[attr].blank? }
+  end
 end

app/views/ldap_group_links/_ldap_group_link.html.haml

@@ -2,7 +2,7 @@
   .pull-right
     = link_to group_ldap_group_link_path(group, ldap_group_link), method: :delete, class: 'btn btn-danger btn-sm' do
       = fa_icon('unlink', text: 'unlink')
-  %strong= ldap_group_link.cn ? "Group: #{ldap_group_link.cn}" : "Filter: #{ldap_group_link.filter}"
+  %strong= ldap_group_link.cn ? "Group: #{ldap_group_link.cn}" : "Filter: #{truncate(ldap_group_link.filter, length: 70)}"
 
   - if ldap_group_link.config
     .light

ee/lib/ee/gitlab/ldap/user_filter.rb

@@ -12,7 +12,11 @@ module EE
         end
 
         def filter
-          @proxy.adapter.ldap_search(options).map(&:dn)
+          logger.debug "Running filter #{@filter} against #{@proxy.provider}"
+
+          @proxy.adapter.ldap_search(options).map(&:dn).tap do |dns|
+            logger.debug "Found #{dns.count} mathing users for filter #{@filter}"
+          end
         end
 
         private
@@ -28,6 +32,10 @@ module EE
         def config
           @proxy.adapter.config
         end
+
+        def logger
+          Rails.logger
+        end
       end
     end
   end