Use RequestStore to memoize Flipper features so that memoized values are cleared between requests

Signed-off-by: Rémy Coutable <remy@rymai.me>

lib/feature.rb

@@ -63,8 +63,15 @@ class Feature
     end
     def flipper
-      Thread.current[:flipper] ||=
-        Flipper.new(flipper_adapter).tap { |flip| flip.memoize = true }
+      if RequestStore.active?
+        RequestStore[:flipper] ||= build_flipper_instance
+      else
+        @flipper ||= build_flipper_instance
+      end
+    end
+
+    def build_flipper_instance
+      Flipper.new(flipper_adapter).tap { |flip| flip.memoize = true }
     end
     # This method is called from config/initializers/flipper.rb and can be used

spec/lib/feature_spec.rb

@@ -64,4 +64,28 @@ describe Feature do
       expect(described_class.all).to eq(features.to_a)
     end
   end
+
+  describe '.flipper' do
+    shared_examples 'a memoized Flipper instance' do
+      it 'memoizes the Flipper instance' do
+        expect(Flipper).to receive(:new).once.and_call_original
+
+        2.times do
+          described_class.flipper
+        end
+      end
+    end
+
+    context 'when request store is inactive' do
+      before do
+        described_class.instance_variable_set(:@flipper, nil)
+      end
+
+      it_behaves_like 'a memoized Flipper instance'
+    end
+
+    context 'when request store is inactive', :request_store do
+      it_behaves_like 'a memoized Flipper instance'
+    end
+  end
 end