User should be able to leave group. If not - show him proper message

CHANGELOG

@@ -29,6 +29,7 @@ v 7.12.0 (unreleased)
   - Clarify navigation labels for Project Settings and Group Settings.
   - Move user avatar and logout button to sidebar
   - You can not remove user if he/she is an only owner of group
+  - User should be able to leave group. If not - show him proper message
 
 v 7.11.4
   - Fix missing bullets when creating lists

app/controllers/groups/group_members_controller.rb

@@ -66,9 +66,13 @@ class Groups::GroupMembersController < Groups::ApplicationController
       @group_member.destroy
       redirect_to(dashboard_groups_path, notice: "You left #{group.name} group.")
     else
+      if @group.last_owner?(current_user)
+        redirect_to(dashboard_groups_path, alert: "You can not leave #{group.name} group because you're the last owner. Transfer or delete the group.")
+      else
         return render_403
       end
     end
+  end
 
   protected
 

app/views/dashboard/groups/index.html.haml

@@ -23,8 +23,7 @@
               %i.fa.fa-cogs
               Settings
 
-          - if can?(current_user, :destroy_group_member, group_member)
-            = link_to leave_group_group_members_path(group), data: { confirm: leave_group_message(group.name) }, method: :delete, class: "btn-sm btn btn-grouped", title: 'Remove user from group' do
+          = link_to leave_group_group_members_path(group), data: { confirm: leave_group_message(group.name) }, method: :delete, class: "btn-sm btn btn-grouped", title: 'Leave this group' do
             %i.fa.fa-sign-out
             Leave