fix sections_visible_to for array arguments

test plan:
* create a course with at least 2 sections
* enroll a teacher or ta both sections,
 checking "Can grade students in their section only"

* as the teacher/ta, visit the inbox
and start composing a message
* select the course
* use the address book button, click on "Course Sections",
 and then a specific section
* should not recieve a 500 network error

fixes #CNVS-16585

Change-Id: I99511bc46a67fd425c3eefde8cec2d9e275454d4
Reviewed-on: https://gerrit.instructure.com/44737
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>

app/models/course.rb

@@ -2163,22 +2163,22 @@ class Course < ActiveRecord::Base
       else scope.none
     end
   end
-
+  
   def sections_visible_to(user, sections = active_course_sections)
     visibilities = section_visibilities_for(user)
+    visibility = enrollment_visibility_level_for(user, visibilities)
     section_ids = visibilities.map{ |s| s[:course_section_id] }
-    case enrollment_visibility_level_for(user, visibilities)
-    when :full, :limited
-      if visibilities.all?{ |v| ['StudentEnrollment', 'StudentViewEnrollment', 'ObserverEnrollment'].include? v[:type] }
-        sections.where(:id => section_ids)
+    is_scope = sections.respond_to?(:where)
+
+    if [:full, :limited, :sections].include?(visibility)
+      if visibility == :sections || visibilities.all?{ |v| ['StudentEnrollment', 'StudentViewEnrollment', 'ObserverEnrollment'].include? v[:type] }
+        is_scope ? sections.where(:id => section_ids) : sections.select{|section| section_ids.include?(section.id)}
       else
         sections
       end
-    when :sections
-      sections.where(:id => section_ids)
     else
       # return an empty set, but keep it as a scope for downstream consistency
-      sections.none
+      is_scope ? sections.none : []
     end
   end
 

spec/helpers/search_helper_spec.rb

@@ -45,6 +45,15 @@ describe SearchHelper do
       expect(@contexts[:sections].count).to eq 1
     end
 
+    it "loads the section even with restricted privileges" do
+      course_with_teacher(:active_all => true, :limit_privileges_to_course_section => true)
+      @current_user = @teacher
+      load_all_contexts(context: @course.default_section)
+
+      expect(@contexts[:courses].count).to eq 1
+      expect(@contexts[:sections].count).to eq 1
+    end
+
     describe "sharding" do
       specs_require_sharding