created can_manage_comments helper for rendering button

app/helpers/application_helper.rb

@@ -263,6 +263,10 @@ module ApplicationHelper
     end
   end
 
+  def can_manage_comments(conference)
+    (current_user.has_role? :organizer, conference) || (current_user.has_role? :cfp, conference)
+  end
+
   def sign_in_path
     if CONFIG['authentication']['ichain']['enabled']
       new_user_ichain_session_path

app/models/ability.rb

@@ -137,7 +137,7 @@ class Ability
     can :manage, Sponsor, conference_id: conf_ids_for_organizer
     can :manage, SponsorshipLevel, conference_id: conf_ids_for_organizer
     can :manage, Ticket, conference_id: conf_ids_for_organizer
-    can [:index, :create], Comment, commentable_type: 'Event',
+    can :index, Comment, commentable_type: 'Event',
                                     commentable_id: Event.where(conference_id: conf_ids_for_organizer).pluck(:id)
   end
 
@@ -157,7 +157,7 @@ class Ability
     can :manage, CallForPaper, conference_id: conf_ids_for_cfp
     can :manage, Commercial, commercialable_type: 'Event',
                              commercialable_id: Event.where(conference_id: conf_ids_for_cfp).pluck(:id)
-    can [:index, :create], Comment, commentable_type: 'Event',
+    can :index, Comment, commentable_type: 'Event',
                                     commentable_id: Event.where(conference_id: conf_ids_for_cfp).pluck(:id)
   end
 

app/views/layouts/_navigation.html.haml

@@ -25,7 +25,7 @@
                 %b.caret
               %ul.dropdown-menu
                 = render 'layouts/user_menu'
-          - if can? :index, Comment #TODO modify condition
+          - if can_manage_comments(@conference)
             %ul.nav.navbar-nav.navbar-right
               %li.dropdown
                 %a.dropdown-toggle{"data-toggle" => "dropdown", :href => "#", id: "unread-comments-preview"}