don't load all contexts for group recipient lookup

fixes CNVS-18578

test plan
quauntitative functionality test
- regression test recipient picker when picking in groups

qualitative speed test
- have a high enrollment user with normally slow response times
 during conversation recipient finding
- compose a conversation message
- search for recipients in a group using the dropdown recipient
 picker
- ensure that the response time for the recipient is not as bad
 as it was

Change-Id: Ie7655544f93d1168ac78f0b1497c1bec9f0319c6
Reviewed-on: https://gerrit.instructure.com/49395
Tested-by: Jenkins
Reviewed-by: Matthew Wheeler <mwheeler@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Joel Hough <joel@instructure.com>

app/helpers/search_helper.rb

@@ -99,6 +99,11 @@ def load_all_contexts(options = {})
         end
         add_sections.call sections
         add_groups.call context.groups.active, context
+      elsif context.is_a?(Group)
+        if context.grants_right?(@current_user, session, :read)
+          add_groups.call [context]
+          add_courses.call [context.context], :current if context.context.is_a?(Course)
+        end
       elsif context.is_a?(CourseSection)
         visibility = context.course.enrollment_visibility_level_for(@current_user, context.course.section_visibilities_for(@current_user), true)
         sections = (visibility == :restricted) ? [] : [context]

spec/helpers/search_helper_spec.rb

@@ -45,6 +45,18 @@
       expect(@contexts[:sections].count).to eq 1
     end
 
+    it "only loads the group and its course when given a group context" do
+      course_with_teacher(:active_all => true)
+      course_with_teacher(:active_all => true, :user => @teacher)
+      @current_user = @teacher
+      group_model(context: @course)
+      load_all_contexts(context: @group)
+
+      expect(@contexts[:courses].count).to eq 1
+      expect(@contexts[:groups].count).to eq 1
+      expect(@contexts[:sections].count).to eq 0
+    end
+
     it "loads the section even with section-restricted teacher privileges" do
       course_with_teacher(:active_all => true, :limit_privileges_to_course_section => true)
       @current_user = @teacher