show groupless submissions in speedgrader

fixes CNVS-15753

Test plan:
  * make a group assignment with a group category that has no groups
  * submit some homework
  * the submissions should display (and be gradeable) in speedgrader
  * add some groups (with people in them)
  * submit more homework for the people with groups
  * the submissions for people in groups and people not in groups
    should all display
  * downloading submissions should work as well

Change-Id: I7e6081cec61936c4f833394e995963698f4b57b7
Reviewed-on: https://gerrit.instructure.com/41596
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Matt Berns <mberns@instructure.com>
Reviewed-by: Mike Nomitch <mnomitch@instructure.com>
QA-Review: Sean Lewis <slewis@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>

app/models/assignment.rb

@@ -1395,9 +1395,7 @@ class Assignment < ActiveRecord::Base
                                  else
                                    []
                                  end
-      group_category.groups.includes(:group_memberships => :user).map { |g|
-        [g.name, g.users]
-      }.map { |group_name, group_students|
+      groups_and_ungrouped(user).map { |group_name, group_students|
         visible_group_students = group_students & visible_students_for_speed_grader(user)
         representative   = (visible_group_students & users_with_turnitin_data).first
         representative ||= (visible_group_students & users_with_submissions).first
@@ -1419,6 +1417,17 @@ class Assignment < ActiveRecord::Base
     end
   end
 
+  def groups_and_ungrouped(user)
+    groups_and_users = group_category.
+      groups.includes(:group_memberships => :user).
+      map { |g| [g.name, g.users] }
+    users_in_group = groups_and_users.flat_map { |_,users| users }
+    groupless_users = visible_students_for_speed_grader(user) - users_in_group
+    phony_groups = groupless_users.map { |u| [u.name, [u]] }
+    groups_and_users + phony_groups
+  end
+  private :groups_and_ungrouped
+
   # using this method instead of students_with_visibility so we
   # can add the includes and students_visible_to/participating_students scopes
   def visible_students_for_speed_grader(user)

spec/models/assignment_spec.rb

@@ -2501,6 +2501,7 @@ describe Assignment do
 
     context "group assignments" do
       before :once do
+        course_with_teacher(active_all: true)
         gc = @course.group_categories.create! name: "Assignment Groups"
         @groups = 2.times.map { |i| gc.groups.create! name: "Group #{i}", context: @course }
         students = create_users_in_course(@course, 4, return_type: :record)
@@ -2551,6 +2552,11 @@ describe Assignment do
         s.update_attribute :submission_type, 'online_upload'
         @assignment.representatives(@teacher).should include g1rep
       end
+
+      it "includes users who aren't in a group" do
+        student_in_course active_all: true
+        @assignment.representatives(@teacher).last.should == @student
+      end
     end
 
     context "quizzes" do