Disable Flipper memoization without RequestStore

With RequestStore, it is safe to memoize the feature flag values because
they will be cleared on the next request. Without RequestStore, we can
still memoize the Flipper instance but we must not enable memoization of
feature flag values because those would be permanent until the process
is restarted.

lib/feature.rb

@@ -155,13 +155,13 @@ class Feature
 
     def flipper
       if Gitlab::SafeRequestStore.active?
-        Gitlab::SafeRequestStore[:flipper] ||= build_flipper_instance
+        Gitlab::SafeRequestStore[:flipper] ||= build_flipper_instance(memoize: true)
       else
         @flipper ||= build_flipper_instance
       end
     end
 
-    def build_flipper_instance
+    def build_flipper_instance(memoize: false)
       active_record_adapter = Flipper::Adapters::ActiveRecord.new(
         feature_class: FlipperFeature,
         gate_class: FlipperGate)
@@ -182,7 +182,7 @@ class Feature
         expires_in: 1.minute)
 
       Flipper.new(flipper_adapter).tap do |flip|
-        flip.memoize = true
+        flip.memoize = memoize
       end
     end
 

spec/lib/feature_spec.rb

@@ -102,12 +102,14 @@ RSpec.describe Feature, stub_feature_flags: false do
 
   describe '.flipper' do
     context 'when request store is inactive' do
-      it 'memoizes the Flipper instance' do
+      it 'memoizes the Flipper instance but does not not enable Flipper memoization' do
         expect(Flipper).to receive(:new).once.and_call_original
 
         2.times do
-          described_class.send(:flipper)
+          described_class.flipper
         end
+
+        expect(described_class.flipper.adapter.memoizing?).to eq(false)
       end
     end
 
@@ -115,9 +117,11 @@ RSpec.describe Feature, stub_feature_flags: false do
       it 'memoizes the Flipper instance' do
         expect(Flipper).to receive(:new).once.and_call_original
 
-        described_class.send(:flipper)
+        described_class.flipper
         described_class.instance_variable_set(:@flipper, nil)
-        described_class.send(:flipper)
+        described_class.flipper
+
+        expect(described_class.flipper.adapter.memoizing?).to eq(true)
       end
     end
   end