Record issues added to epic on usage ping

Record issues addded to epic by users
using HLL redis counters.

doc/development/usage_ping/dictionary.md

@@ -9812,6 +9812,30 @@ Status: `implemented`
 
 Tiers: `premium`, `ultimate`
 
+### `redis_hll_counters.epics_usage.g_project_management_epic_issue_added_monthly`
+
+Count of MAU adding issues to epics
+
+[YAML definition](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/config/metrics/counts_28d/20210312144719_g_product_planning_epic_issue_added_monthly.yml)
+
+Group: `group::product planning`
+
+Status: `implemented`
+
+Tiers: `premium`, `ultimate`
+
+### `redis_hll_counters.epics_usage.g_project_management_epic_issue_added_weekly`
+
+Count of WAU adding issues to epics
+
+[YAML definition](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/config/metrics/counts_7d/20210312181918_g_product_planning_epic_issue_added_weekly.yml)
+
+Group: `group::product planning`
+
+Status: `implemented`
+
+Tiers: `premium`, `ultimate`
+
 ### `redis_hll_counters.epics_usage.g_project_management_users_destroying_epic_notes_monthly`
 
 Counts of MAU destroying epic notes

ee/app/services/epic_issues/create_service.rb

@@ -19,6 +19,7 @@ module EpicIssues
 
       if link.save
         create_notes(referenced_issue, params)
+        usage_ping_record_epic_issue_added
       end
 
       link
@@ -64,5 +65,9 @@ module EpicIssues
     def issuable_group_descendants
       @descendants ||= issuable.group.self_and_descendants
     end
+
+    def usage_ping_record_epic_issue_added
+      ::Gitlab::UsageDataCounters::EpicActivityUniqueCounter.track_epic_issue_added(author: current_user)
+    end
   end
 end

ee/changelogs/unreleased/issue_292253-track_epic_issue.yml

+---
+title: Record issues added to epic on usage ping
+merge_request: 56559
+author:
+type: other

ee/config/metrics/counts_28d/20210312144719_g_product_planning_epic_issue_added_monthly.yml

+---
+# Name of this metric contains g_project_management prefix
+# because we are using the same slot from issue_tracking to
+# allow data aggregation.
+key_path: redis_hll_counters.epics_usage.g_project_management_epic_issue_added_monthly
+description: Count of MAU adding issues to epics
+product_section: dev
+product_stage: plan
+product_group: group::product planning
+product_category: epics_usage
+value_type: number
+status: implemented
+milestone: "13.11"
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/56559
+time_frame: 28d
+data_source: redis_hll
+distribution:
+- ee
+tier:
+- premium
+- ultimate

ee/config/metrics/counts_7d/20210312181918_g_product_planning_epic_issue_added_weekly.yml

+---
+# Name of this metric contains g_project_management prefix
+# because we are using the same slot from issue_tracking to
+# allow data aggregation.
+key_path: redis_hll_counters.epics_usage.g_project_management_epic_issue_added_weekly
+description: Count of WAU adding issues to epics
+product_section: dev
+product_stage: plan
+product_group: group::product planning
+product_category: epics_usage
+value_type: number
+status: implemented
+milestone: "13.11"
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/56559
+time_frame: 7d
+data_source: redis_hll
+distribution:
+- ee
+tier:
+- premium
+- ultimate

ee/lib/gitlab/usage_data_counters/epic_activity_unique_counter.rb

@@ -12,6 +12,7 @@ module Gitlab
       EPIC_NOTE_DESTROYED = 'g_project_management_users_destroying_epic_notes'
       EPIC_START_DATE_SET_AS_FIXED = 'g_project_management_users_setting_epic_start_date_as_fixed'
       EPIC_START_DATE_SET_AS_INHERITED = 'g_project_management_users_setting_epic_start_date_as_inherited'
+      EPIC_ISSUE_ADDED = 'g_project_management_epic_issue_added'
 
       class << self
         def track_epic_created_action(author:, time: Time.zone.now)
@@ -34,6 +35,10 @@ module Gitlab
           track_unique_action(EPIC_START_DATE_SET_AS_INHERITED, author, time)
         end
 
+        def track_epic_issue_added(author:, time: Time.zone.now)
+          track_unique_action(EPIC_ISSUE_ADDED, author, time)
+        end
+
         private
 
         def track_unique_action(action, author, time)

ee/spec/lib/gitlab/usage_data_counters/epic_activity_unique_counter_spec.rb

@@ -69,4 +69,16 @@ RSpec.describe Gitlab::UsageDataCounters::EpicActivityUniqueCounter, :clean_gitl
       it_behaves_like 'does not track when feature flag is disabled', :track_epics_activity
     end
   end
+
+  context 'for adding issue to epic event' do
+    def track_action(params)
+      described_class.track_epic_issue_added(**params)
+    end
+
+    it_behaves_like 'a daily tracked issuable event' do
+      let(:action) { described_class::EPIC_ISSUE_ADDED }
+    end
+
+    it_behaves_like 'does not track when feature flag is disabled', :track_epics_activity
+  end
 end

ee/spec/services/epic_issues/create_service_spec.rb

@@ -66,6 +66,12 @@ RSpec.describe EpicIssues::CreateService do
         expect(note.noteable_type).to eq('Issue')
         expect(note.system_note_metadata.action).to eq('issue_added_to_epic')
       end
+
+      it 'records action on usage ping' do
+        expect(::Gitlab::UsageDataCounters::EpicActivityUniqueCounter).to receive(:track_epic_issue_added).with(author: user)
+
+        subject
+      end
     end
 
     shared_examples 'returns an error' do

lib/gitlab/usage_data_counters/known_events/epic_events.yml

@@ -32,3 +32,9 @@
   redis_slot: project_management
   aggregation: daily
   feature_flag: track_epics_activity
+
+- name: g_project_management_epic_issue_added
+  category: epics_usage
+  redis_slot: project_management
+  aggregation: daily
+  feature_flag: track_epics_activity