cache all feature flags on root accounts

since they are the most common target of feature flag predicates

Change-Id: I2c6be68f442b2eb66f8cd5ad57cafbc83f114ba1
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/271502
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>

app/models/account.rb

@@ -1574,6 +1574,7 @@ class Account < ActiveRecord::Base
 
   # an opportunity for plugins to load some other stuff up before caching the account
   def precache
+    feature_flags.load
   end
 
   class ::Canvas::AccountCacheError < StandardError; end

app/models/feature_flag.rb

@@ -64,22 +64,25 @@ class FeatureFlag < ActiveRecord::Base
   end
 
   def clear_cache
-    if self.context
-      self.class.connection.after_transaction_commit { self.context.feature_flag_cache.delete(self.context.feature_flag_cache_key(feature)) }
-      self.context.touch if Feature.definitions[feature].try(:touch_context)
-      if self.context.is_a?(Account)
-        if self.context.site_admin?
-          Switchman::DatabaseServer.send_in_each_region(self.context, :clear_cache_key, {}, :feature_flags)
+    if context
+      self.class.connection.after_transaction_commit do
+        context.feature_flag_cache.delete(context.feature_flag_cache_key(feature))
+        context.touch if Feature.definitions[feature].try(:touch_context) || context.try(:root_account?)
+
+          if context.is_a?(Account)
+          if context.site_admin?
+            Switchman::DatabaseServer.send_in_each_region(context, :clear_cache_key, {}, :feature_flags)
           else
-          self.context.clear_cache_key(:feature_flags)
+            context.clear_cache_key(:feature_flags)
           end
         end
 
-      if ::Rails.env.development? && self.context.is_a?(Account) && Account.all_special_accounts.include?(self.context)
+        if !::Rails.env.production? && context.is_a?(Account) && Account.all_special_accounts.include?(context)
           Account.clear_special_account_cache!(true)
         end
       end
     end
+  end
 
   def audit_log_update(operation: :update)
     # kill switch in case something goes crazy in rolling this out.

lib/feature_flags.rb

@@ -45,12 +45,12 @@ module FeatureFlags
 
   def set_feature_flag!(feature, state)
     feature = feature.to_s
-    flag = self.feature_flags.where(feature: feature).first
-    flag ||= self.feature_flags.build(feature: feature)
+    flag = feature_flags.find_or_initialize_by(feature: feature)
     flag.state = state
     @feature_flag_cache ||= {}
     @feature_flag_cache[feature] = flag
     flag.save!
+    association(:feature_flags).reset
   end
 
   def allow_feature!(feature)
@@ -141,6 +141,10 @@ module FeatureFlags
     # find the highest flag that doesn't allow override,
     # or the most specific flag otherwise
     accounts = feature_flag_account_ids.map do |id|
+      # optimizations for accounts we likely already have loaded (including their feature flags!)
+      next Account.site_admin if id == Account.site_admin.global_id
+      next Account.current_domain_root_account if id == Account.current_domain_root_account&.global_id
+
       account = Account.new
       account.id = id
       account.shard = Shard.shard_for(id, self.shard)
@@ -150,9 +154,10 @@ module FeatureFlags
 
     all_contexts = (accounts + [self]).uniq
     all_contexts -= [self] if inherited_only
-    all_contexts.each_with_index do |context, idx|
+    all_contexts.each do |context|
       flag = context.feature_flag(feature, skip_cache: context == self && skip_cache)
       next unless flag
+
       retval = flag
       break unless flag.can_override?
     end

spec/models/enrollment_spec.rb

@@ -2977,6 +2977,7 @@ describe Enrollment do
       before :each do
         course_with_student
         @course.root_account.enable_feature!(:granular_permissions_manage_users)
+        @enrollment.reload
       end
 
       it 'is true for a user who has been granted :manage_students' do
@@ -3041,6 +3042,7 @@ describe Enrollment do
       before :each do
         course_with_observer
         @course.root_account.enable_feature!(:granular_permissions_manage_users)
+        @enrollment.reload
       end
 
       it 'is true with :manage_students' do
@@ -3074,6 +3076,7 @@ describe Enrollment do
       before :each do
         course_with_teacher
         @course.root_account.enable_feature!(:granular_permissions_manage_users)
+        @enrollment.reload
       end
 
       it 'is false with :manage_students' do

spec/models/quizzes/quiz_spec.rb

@@ -1147,7 +1147,7 @@ describe Quizzes::Quiz do
     end
 
     it "returns false when feature flag is off" do
-      @course.root_account.set_feature_flag! 'timer_without_autosubmission', 'off'
+      @quiz.context.root_account.set_feature_flag! 'timer_without_autosubmission', 'off'
       expect(@quiz.timer_autosubmit_disabled?).to be(false)
       @quiz.update({
         disable_timer_autosubmission: true
@@ -1156,12 +1156,12 @@ describe Quizzes::Quiz do
     end
 
     it "returns false when feature flag is on and disable_timer_autosubmission is false" do
-      @course.root_account.set_feature_flag! 'timer_without_autosubmission', 'on'
+      @quiz.context.root_account.set_feature_flag! 'timer_without_autosubmission', 'on'
       expect(@quiz.timer_autosubmit_disabled?).to be(false)
     end
 
     it "returns true when feature flag is on and disable_timer_autosubmission is true" do
-      @course.root_account.set_feature_flag! 'timer_without_autosubmission', 'on'
+      @quiz.context.root_account.set_feature_flag! 'timer_without_autosubmission', 'on'
       @quiz.update({
         disable_timer_autosubmission: true
       })

spec/views/courses/settings.html.erb_spec.rb

@@ -145,6 +145,7 @@ describe "courses/settings.html.erb" do
     end
 
     before :each do
+      @course.root_account.reload
       view_context(@course, @teacher)
     end
 
@@ -247,7 +248,7 @@ describe "courses/settings.html.erb" do
     end
 
     context "with the feature enabled" do
-      before { Account.default.enable_feature!(:course_templates) }
+      before { @course.root_account.enable_feature!(:course_templates) }
 
       it "is visible" do
         render