Track epic destroy note via usage ping

- Add usage ping metrics files

doc/development/usage_ping/dictionary.md

@@ -9812,6 +9812,30 @@ Status: `implemented`
 
 Tiers: `premium`, `ultimate`
 
+### `redis_hll_counters.epics_usage.g_project_management_users_destroying_epic_notes_monthly`
+
+Counts of MAU destroying epic notes
+
+[YAML definition](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/config/metrics/counts_28d/20210315034808_g_project_management_users_destroying_epic_notes_monthly.yml)
+
+Group: `group:product planning`
+
+Status: `implemented`
+
+Tiers: `premium`, `ultimate`
+
+### `redis_hll_counters.epics_usage.g_project_management_users_destroying_epic_notes_weekly`
+
+Counts of WAU destroying epic notes
+
+[YAML definition](https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/config/metrics/counts_7d/20210315034846_g_project_management_users_destroying_epic_notes_weekly.yml)
+
+Group: `group:product planning`
+
+Status: `implemented`
+
+Tiers: `premium`, `ultimate`
+
 ### `redis_hll_counters.ide_edit.g_edit_by_sfe_monthly`
 
 Missing description

ee/app/services/ee/notes/destroy_service.rb

@@ -11,6 +11,14 @@ module EE
 
         ::Analytics::RefreshCommentsData.for_note(note)&.execute(force: true)
         ::Gitlab::StatusPage.trigger_publish(project, current_user, note)
+
+        track_note_removal_usage_epics if note.for_epic?
+      end
+
+      private
+
+      def track_note_removal_usage_epics
+        ::Gitlab::UsageDataCounters::EpicActivityUniqueCounter.track_epic_note_destroyed_action(author: current_user)
       end
     end
   end

ee/changelogs/unreleased/292253-cablett-track-destroy-epic-note.yml

+---
+title: Track epic note destroyed
+merge_request: 56617
+author:
+type: other

ee/config/metrics/counts_28d/20210315034808_g_project_management_users_destroying_epic_notes_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_users_destroying_epic_notes_monthly
+description: Counts of MAU destroying epic notes
+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/56617
+time_frame: 28d
+data_source: redis_hll
+distribution:
+- ee
+tier:
+- premium
+- ultimate

ee/config/metrics/counts_7d/20210315034846_g_project_management_users_destroying_epic_notes_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_users_destroying_epic_notes_weekly
+description: Counts of WAU destroying epic notes
+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/56617
+time_frame: 7d
+data_source: redis_hll
+distribution:
+- ee
+tier:
+- premium
+- ultimate

ee/lib/gitlab/usage_data_counters/epic_activity_unique_counter.rb

@@ -8,12 +8,17 @@ module Gitlab
       # slot of issue events to allow data aggregation.
       # More information in: https://gitlab.com/gitlab-org/gitlab/-/issues/322405
       EPIC_CREATED = 'g_project_management_epic_created'
+      EPIC_NOTE_DESTROYED = 'g_project_management_users_destroying_epic_notes'
 
       class << self
         def track_epic_created_action(author:, time: Time.zone.now)
           track_unique_action(EPIC_CREATED, author, time)
         end
 
+        def track_epic_note_destroyed_action(author:, time: Time.zone.now)
+          track_unique_action(EPIC_NOTE_DESTROYED, author, time)
+        end
+
         private
 
         def track_unique_action(action, author, time)

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

@@ -19,4 +19,16 @@ RSpec.describe Gitlab::UsageDataCounters::EpicActivityUniqueCounter, :clean_gitl
 
     it_behaves_like 'does not track when feature flag is disabled', :track_epics_activity
   end
+
+  context 'for epic note destroyed event' do
+    def track_action(params)
+      described_class.track_epic_note_destroyed_action(**params)
+    end
+
+    it_behaves_like 'a daily tracked issuable event' do
+      let(:action) { described_class::EPIC_NOTE_DESTROYED }
+    end
+
+    it_behaves_like 'does not track when feature flag is disabled', :track_epics_activity
+  end
 end

ee/spec/services/ee/notes/destroy_service_spec.rb

@@ -31,5 +31,17 @@ RSpec.describe Notes::DestroyService do
 
       include_examples 'trigger status page publish'
     end
+
+    describe 'tracking via usage ping' do
+      let_it_be(:note) do
+        create(:note_on_epic, author: user)
+      end
+
+      it 'tracks epic note destroy' do
+        expect(::Gitlab::UsageDataCounters::EpicActivityUniqueCounter).to receive(:track_epic_note_destroyed_action)
+
+        service.execute(note)
+      end
+    end
   end
 end

lib/gitlab/usage_data_counters/known_events/epic_events.yml

@@ -8,3 +8,9 @@
   redis_slot: project_management
   aggregation: daily
   feature_flag: track_epics_activity
+
+- name: g_project_management_users_destroying_epic_notes
+  category: epics_usage
+  redis_slot: project_management
+  aggregation: daily
+  feature_flag: track_epics_activity

spec/lib/gitlab/usage_data_spec.rb

@@ -1358,7 +1358,7 @@ RSpec.describe Gitlab::UsageData, :aggregate_failures do
 
     let(:categories) { ::Gitlab::UsageDataCounters::HLLRedisCounter.categories }
     let(:ineligible_total_categories) do
-      %w[source_code ci_secrets_management incident_management_alerts snippets terraform epics_usage]
+      %w[source_code ci_secrets_management incident_management_alerts snippets terraform]
     end
 
     it 'has all known_events' do