Add feature flag mechanism to aggregated metrics

In order to enable for more controll when adding
product analytics aggregated metrics, we need to implement logic
that will check feature flags defined for each of the aggregated
metrics definition.

doc/development/product_analytics/usage_ping.md

@@ -737,13 +737,20 @@ In order to add data for aggregated metrics into Usage Ping payload you should a
 - operator: operator that defines how aggregated metric data will be counted. Available operators are:
   - `ANY`: removes duplicates and counts all entries that triggered any of listed events
 - events: list of events names (from [`known_events.yml`](#known-events-in-usage-data-payload)) to aggregate into metric. All events in this list must have the same `redis_slot` and `aggregation` attributes.
+- feature_flag: name of [development feature flag](../feature_flags/development.md#development-type) that will be checked before
+metrics aggregation is performed. Corresponding feature flag should have `default_enabled` attribute set to `false`. 
+`feature_flag` attribute is **OPTIONAL**  and can be omitted, when `feature_flag` is missing no feature flag will be checked.
 
-Example aggregated metric entry:
+Example aggregated metric entries:
 
 ```yaml
 - name: example_aggregated_metric
+  operator: ANY
+  events: ['i_search_advanced', 'i_search_paid']
+- name: example_aggregated_metric_with_feautre_flag
   operator: ANY
   events: ['i_search_total', 'i_search_advanced', 'i_search_paid']
+  feature_flag: example_aggregated_metric
 ```
 
 Aggregated metrics will be added under `aggregated_metrics` key in both `counts_weekly` and `counts_monthly` top level keys in Usage Ping payload.

lib/gitlab/usage_data_counters/aggregated_metrics/common.yml

@@ -4,10 +4,15 @@
 #             - "ALL": counts unique elements that were observed triggering all of following events
 #  events: list of events names to aggregate into metric. All events in this list must have the same 'redis_slot' and 'aggregation' attributes
 #           see from lib/gitlab/usage_data_counters/known_events/ for the list of valid events.
+#  feature_flag: name of development feature flag that will be checked before metrics aggregation is performed.
+#                Corresponding feature flag should have `default_enabled` attribute set to `false`.
+#                This attribute is OPTIONAL and can be omitted, when `feature_flag` is missing no feature flag will be checked.
 ---
 - name: product_analytics_test_aggregated_metrics
   operator: ANY
   events: ['i_search_total', 'i_search_advanced', 'i_search_paid']
+  feature_flag: product_analytics_aggregated_metrics
 - name: product_analytics_test_combined_events
   operator: ALL
   events: ['i_search_total', 'i_search_advanced', 'i_search_paid']
+  feature_flag: product_analytics_aggregated_metrics

lib/gitlab/usage_data_counters/hll_redis_counter.rb

@@ -97,15 +97,11 @@ module Gitlab
         end
 
         def aggregated_metrics_monthly_data
-          aggregated_metrics.to_h do |aggregation|
-            [aggregation[:name], calculate_count_for_aggregation(aggregation, start_date: 4.weeks.ago.to_date, end_date: Date.current)]
-          end
+          aggregated_metrics_data(4.weeks.ago.to_date)
         end
 
         def aggregated_metrics_weekly_data
-          aggregated_metrics.to_h do |aggregation|
-            [aggregation[:name], calculate_count_for_aggregation(aggregation, start_date: 7.days.ago.to_date, end_date: Date.current)]
-          end
+          aggregated_metrics_data(7.days.ago.to_date)
         end
 
         def known_events
@@ -132,6 +128,14 @@ module Gitlab
           Plan.all_plans
         end
 
+        def aggregated_metrics_data(start_date)
+          aggregated_metrics.each_with_object({}) do |aggregation, weekly_data|
+            next if aggregation[:feature_flag] && Feature.disabled?(aggregation[:feature_flag], default_enabled: false, type: :development)
+
+            weekly_data[aggregation[:name]] = calculate_count_for_aggregation(aggregation, start_date: start_date, end_date: Date.current)
+          end
+        end
+
         def calculate_count_for_aggregation(aggregation, start_date:, end_date:)
           case aggregation[:operator]
           when UNION_OF_AGGREGATED_METRICS

spec/lib/gitlab/usage_data_counters/aggregated_metrics_spec.rb

@@ -33,7 +33,7 @@ RSpec.describe 'aggregated metrics' do
         end
 
         it "has expected structure" do
-          expect(aggregate.keys).to match_array(%w[name operator events])
+          expect(aggregate.keys).to include(*%w[name operator events])
         end
 
         it "uses allowed aggregation operators" do

spec/lib/gitlab/usage_data_counters/hll_redis_counter_spec.rb

@@ -441,6 +441,28 @@ RSpec.describe Gitlab::UsageDataCounters::HLLRedisCounter, :clean_gitlab_redis_s
             expect(aggregated_metrics_data).to eq(results)
           end
         end
+
+        context 'hidden behind feature flag' do
+          let(:enabled_feature_flag) { 'test_ff_enabled' }
+          let(:disabled_feature_flag) { 'test_ff_disabled' }
+          let(:aggregated_metrics) do
+            [
+              # represents stable aggregated metrics that has been fully released
+              { name: 'gmau_without_ff', events: %w[event3_slot event5_slot], operator: "ANY" },
+              # represents new aggregated metric that is under performance testing on gitlab.com
+              { name: 'gmau_enabled', events: %w[event4], operator: "ALL", feature_flag: enabled_feature_flag },
+              # represents aggregated metric that is under development and shouldn't be yet collected even on gitlab.com
+              { name: 'gmau_disabled', events: %w[event4], operator: "ALL", feature_flag: disabled_feature_flag }
+            ].map(&:with_indifferent_access)
+          end
+
+          it 'returns the number of unique events for all known events' do
+            skip_feature_flags_yaml_validation
+            stub_feature_flags(enabled_feature_flag => true, disabled_feature_flag => false)
+
+            expect(aggregated_metrics_data).to eq('gmau_without_ff' => 2, 'gmau_enabled' => 3)
+          end
+        end
       end
     end