Add tracking to merge request lables/milestone changes

We need to track how many users change the labels and milestone for
MRs.

To get that, whenever the labels and milestone changes for a merge
request, we track the following events:

- i_code_review_user_labels_changed
- i_code_review_user_milestone_changed

app/services/merge_requests/update_service.rb

@@ -50,6 +50,7 @@ module MergeRequests
       track_title_and_desc_edits(changed_fields)
       track_discussion_lock_toggle(merge_request, changed_fields)
       track_time_estimate_and_spend_edits(merge_request, old_timelogs, changed_fields)
+      track_labels_change(merge_request, old_labels)
 
       notify_if_labels_added(merge_request, old_labels)
       notify_if_mentions_added(merge_request, old_mentioned_users)
@@ -113,6 +114,12 @@ module MergeRequests
       merge_request_activity_counter.track_time_spent_changed_action(user: current_user) if old_timelogs != merge_request.timelogs
     end
 
+    def track_labels_change(merge_request, old_labels)
+      return if Set.new(merge_request.labels) == Set.new(old_labels)
+
+      merge_request_activity_counter.track_labels_changed_action(user: current_user)
+    end
+
     def notify_if_labels_added(merge_request, old_labels)
       added_labels = merge_request.labels - old_labels
 
@@ -191,6 +198,8 @@ module MergeRequests
 
       return unless merge_request.previous_changes.include?('milestone_id')
 
+      merge_request_activity_counter.track_milestone_changed_action(user: current_user)
+
       if merge_request.milestone.nil?
         notification_service.async.removed_milestone_merge_request(merge_request, current_user)
       else

changelogs/unreleased/292824-track-label-milestone-change.yml

+---
+title: Add tracking to merge request labels/milestone changes
+merge_request: 55484
+author:
+type: other

config/feature_flags/development/usage_data_i_code_review_user_labels_changed.yml

+---
+name: usage_data_i_code_review_user_labels_changed
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55484
+rollout_issue_url:
+milestone: '13.10'
+type: development
+group: group::code review
+default_enabled: true

config/feature_flags/development/usage_data_i_code_review_user_milestone_changed.yml

+---
+name: usage_data_i_code_review_user_milestone_changed
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55484
+rollout_issue_url:
+milestone: '13.10'
+type: development
+group: group::code review
+default_enabled: true

config/metrics/counts_28d/20210302110520_i_code_review_user_milestone_changed_monthly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_user_milestone_changed_monthly
+description: Count of unique users per month who changed milestone of a MR
+product_section: dev
+product_stage: create
+product_group: group::code review
+product_category: code_review
+value_type: number
+status: implemented
+milestone: "13.10"
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55484
+time_frame: 28d
+data_source: redis_hll
+distribution:
+- ce
+- ee
+tier:
+- free
+- premium
+- ultimate

config/metrics/counts_28d/20210302110607_i_code_review_user_labels_changed_monthly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_user_labels_changed_monthly
+description: Count of unique users per month who changed labels of a MR
+product_section: dev
+product_stage: create
+product_group: group::code review
+product_category: code_review
+value_type: number
+status: implemented
+milestone: "13.10"
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55484
+time_frame: 28d
+data_source: redis_hll
+distribution:
+- ce
+- ee
+tier:
+- free
+- premium
+- ultimate

config/metrics/counts_7d/20210302110403_i_code_review_user_milestone_changed_weekly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_user_milestone_changed_weekly
+description: Count of unique users per week who changed milestone of a MR
+product_section: dev
+product_stage: create
+product_group: group::code review
+product_category: code_review
+value_type: number
+status: implemented
+milestone: "13.10"
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55484
+time_frame: 7d
+data_source: redis_hll
+distribution:
+- ce
+- ee
+tier:
+- free
+- premium
+- ultimate

config/metrics/counts_7d/20210302110548_i_code_review_user_labels_changed_weekly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_user_labels_changed_weekly
+description: Count of unique users per week who changed labels of a MR
+product_section: dev
+product_stage: create
+product_group: group::code review
+product_category: code_review
+value_type: number
+status: implemented
+milestone: "13.10"
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55484
+time_frame: 7d
+data_source: redis_hll
+distribution:
+- ce
+- ee
+tier:
+- free
+- premium
+- ultimate

doc/development/usage_ping/dictionary.md

@@ -8444,6 +8444,30 @@ Status: `data_available`
 
 Tiers: 
 
+### `redis_hll_counters.code_review.i_code_review_user_labels_changed_monthly`
+
+Count of unique users per month who changed labels of a MR
+
+[YAML definition](https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/metrics/counts_28d/20210302110607_i_code_review_user_labels_changed_monthly.yml)
+
+Group: `group::code review`
+
+Status: `implemented`
+
+Tiers: `free`, `premium`, `ultimate`
+
+### `redis_hll_counters.code_review.i_code_review_user_labels_changed_weekly`
+
+Count of unique users per week who changed labels of a MR
+
+[YAML definition](https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/metrics/counts_7d/20210302110548_i_code_review_user_labels_changed_weekly.yml)
+
+Group: `group::code review`
+
+Status: `implemented`
+
+Tiers: `free`, `premium`, `ultimate`
+
 ### `redis_hll_counters.code_review.i_code_review_user_marked_as_draft_monthly`
 
 Missing description
@@ -8492,6 +8516,30 @@ Status: `data_available`
 
 Tiers: 
 
+### `redis_hll_counters.code_review.i_code_review_user_milestone_changed_monthly`
+
+Count of unique users per month who changed milestone of a MR
+
+[YAML definition](https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/metrics/counts_28d/20210302110520_i_code_review_user_milestone_changed_monthly.yml)
+
+Group: `group::code review`
+
+Status: `implemented`
+
+Tiers: `free`, `premium`, `ultimate`
+
+### `redis_hll_counters.code_review.i_code_review_user_milestone_changed_weekly`
+
+Count of unique users per week who changed milestone of a MR
+
+[YAML definition](https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/metrics/counts_7d/20210302110403_i_code_review_user_milestone_changed_weekly.yml)
+
+Group: `group::code review`
+
+Status: `implemented`
+
+Tiers: `free`, `premium`, `ultimate`
+
 ### `redis_hll_counters.code_review.i_code_review_user_mr_discussion_locked_monthly`
 
 Count of unique users per month who locked a MR

lib/gitlab/usage_data_counters/aggregated_metrics/code_review.yml

@@ -48,7 +48,9 @@
     'i_code_review_user_time_estimate_changed',
     'i_code_review_user_time_spent_changed',
     'i_code_review_user_assignees_changed',
-    'i_code_review_user_reviewers_changed'
+    'i_code_review_user_reviewers_changed',
+    'i_code_review_user_milestone_changed',
+    'i_code_review_user_labels_changed'
   ]
 - name: code_review_category_monthly_active_users
   operator: OR
@@ -90,7 +92,9 @@
     'i_code_review_user_time_estimate_changed',
     'i_code_review_user_time_spent_changed',
     'i_code_review_user_assignees_changed',
-    'i_code_review_user_reviewers_changed'
+    'i_code_review_user_reviewers_changed',
+    'i_code_review_user_milestone_changed',
+    'i_code_review_user_labels_changed'
   ]
 - name: code_review_extension_category_monthly_active_users
   operator: OR

lib/gitlab/usage_data_counters/known_events/code_review_events.yml

@@ -194,3 +194,13 @@
   category: code_review
   aggregation: weekly
   feature_flag: usage_data_i_code_review_user_reviewers_changed
+- name: i_code_review_user_milestone_changed
+  redis_slot: code_review
+  category: code_review
+  aggregation: weekly
+  feature_flag: usage_data_i_code_review_user_milestone_changed
+- name: i_code_review_user_labels_changed
+  redis_slot: code_review
+  category: code_review
+  aggregation: weekly
+  feature_flag: usage_data_i_code_review_user_labels_changed

lib/gitlab/usage_data_counters/merge_request_activity_unique_counter.rb

@@ -42,6 +42,8 @@ module Gitlab
       MR_ASSIGNEES_CHANGED_ACTION = 'i_code_review_user_assignees_changed'
       MR_REVIEWERS_CHANGED_ACTION = 'i_code_review_user_reviewers_changed'
       MR_INCLUDING_CI_CONFIG_ACTION = 'o_pipeline_authoring_unique_users_pushing_mr_ciconfigfile'
+      MR_MILESTONE_CHANGED_ACTION = 'i_code_review_user_milestone_changed'
+      MR_LABELS_CHANGED_ACTION = 'i_code_review_user_labels_changed'
 
       class << self
         def track_mr_diffs_action(merge_request:)
@@ -191,6 +193,14 @@ module Gitlab
           track_unique_action_by_user(MR_INCLUDING_CI_CONFIG_ACTION, user)
         end
 
+        def track_milestone_changed_action(user:)
+          track_unique_action_by_user(MR_MILESTONE_CHANGED_ACTION, user)
+        end
+
+        def track_labels_changed_action(user:)
+          track_unique_action_by_user(MR_LABELS_CHANGED_ACTION, user)
+        end
+
         private
 
         def track_unique_action_by_merge_request(action, merge_request)

spec/lib/gitlab/usage_data_counters/merge_request_activity_unique_counter_spec.rb

@@ -370,4 +370,20 @@ RSpec.describe Gitlab::UsageDataCounters::MergeRequestActivityUniqueCounter, :cl
       it_behaves_like 'not tracked merge request unique event'
     end
   end
+
+  describe '.track_milestone_changed_action' do
+    subject { described_class.track_milestone_changed_action(user: user) }
+
+    it_behaves_like 'a tracked merge request unique event' do
+      let(:action) { described_class::MR_MILESTONE_CHANGED_ACTION }
+    end
+  end
+
+  describe '.track_labels_changed_action' do
+    subject { described_class.track_labels_changed_action(user: user) }
+
+    it_behaves_like 'a tracked merge request unique event' do
+      let(:action) { described_class::MR_LABELS_CHANGED_ACTION }
+    end
+  end
 end

spec/services/merge_requests/update_service_spec.rb

@@ -187,6 +187,24 @@ RSpec.describe MergeRequests::UpdateService, :mailer do
           MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
         end
 
+        it 'tracks milestone change' do
+          expect(Gitlab::UsageDataCounters::MergeRequestActivityUniqueCounter)
+            .to receive(:track_milestone_changed_action).once.with(user: user)
+
+          opts[:milestone] = milestone
+
+          MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
+        end
+
+        it 'track labels change' do
+          expect(Gitlab::UsageDataCounters::MergeRequestActivityUniqueCounter)
+            .to receive(:track_labels_changed_action).once.with(user: user)
+
+          opts[:label_ids] = [label2.id]
+
+          MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
+        end
+
         context 'assignees' do
           context 'when assignees changed' do
             it 'tracks assignees changed event' do