Add tracking to merge request assignees/reviewers changes

We need to track how many users change the assignees/reviewers of
MRs.

To get that, whenever the assignees/reviewers changes for a merge
request, we track the following events:

- i_code_review_user_assignees_changed
- i_code_review_user_reviewers_changed

app/services/merge_requests/update_service.rb

@@ -205,6 +205,7 @@ module MergeRequests
 
       new_assignees = merge_request.assignees - old_assignees
       merge_request_activity_counter.track_users_assigned_to_mr(users: new_assignees)
+      merge_request_activity_counter.track_assignees_changed_action(user: current_user)
     end
 
     def handle_reviewers_change(merge_request, old_reviewers)
@@ -216,6 +217,7 @@ module MergeRequests
 
       new_reviewers = merge_request.reviewers - old_reviewers
       merge_request_activity_counter.track_users_review_requested(users: new_reviewers)
+      merge_request_activity_counter.track_reviewers_changed_action(user: current_user)
     end
 
     def create_branch_change_note(issuable, branch_type, event_type, old_branch, new_branch)

changelogs/unreleased/292824-track-assignee-reviewer-changes.yml

+---
+title: Add tracking to merge request assignees/reviewers changes
+merge_request: 55486
+author:
+type: other

config/feature_flags/development/usage_data_i_code_review_user_assignees_changed.yml

+---
+name: usage_data_i_code_review_user_assignees_changed
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55486
+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_reviewers_changed.yml

+---
+name: usage_data_i_code_review_user_reviewers_changed
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55486
+rollout_issue_url:
+milestone: '13.10'
+type: development
+group: group::code review
+default_enabled: true

config/metrics/counts_28d/20210302114145_i_code_review_user_assignees_changed_monthly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_user_assignees_changed_monthly
+description: Count of unique users per month who changed assignees 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/55486
+time_frame: 28d
+data_source: redis_hll
+distribution:
+- ce
+- ee
+tier:
+- free
+- premium
+- ultimate

config/metrics/counts_28d/20210302114219_i_code_review_user_reviewers_changed_monthly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_user_reviewers_changed_monthly
+description: Count of unique users per month who changed reviewers 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/55486
+time_frame: 28d
+data_source: redis_hll
+distribution:
+- ce
+- ee
+tier:
+- free
+- premium
+- ultimate

config/metrics/counts_7d/20210302114202_i_code_review_user_assignees_changed_weekly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_user_assignees_changed_weekly
+description: Count of unique users per week who changed assignees 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/55486
+time_frame: 7d
+data_source: redis_hll
+distribution:
+- ce
+- ee
+tier:
+- free
+- premium
+- ultimate

config/metrics/counts_7d/20210302114235_i_code_review_user_reviewers_changed_weekly.yml

+---
+key_path: redis_hll_counters.code_review.i_code_review_user_reviewers_changed_weekly
+description: Count of unique users per week who changed reviewers 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/55486
+time_frame: 7d
+data_source: redis_hll
+distribution:
+- ce
+- ee
+tier:
+- free
+- premium
+- ultimate

doc/development/usage_ping/dictionary.md

@@ -13004,6 +13004,46 @@ Missing description
 | `tier` |  |
 | `skip_validation` | true |
 
+## `redis_hll_counters.code_review.i_code_review_user_assignees_changed_monthly`
+
+Count of unique users per month who changed assignees of a MR
+
+| field | value |
+| --- | --- |
+| `key_path` | **`redis_hll_counters.code_review.i_code_review_user_assignees_changed_monthly`** |
+| `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` | [Introduced by](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55486) |
+| `time_frame` | 28d |
+| `data_source` | Redis_hll |
+| `distribution` | ce, ee |
+| `tier` | free, premium, ultimate |
+
+## `redis_hll_counters.code_review.i_code_review_user_assignees_changed_weekly`
+
+Count of unique users per week who changed assignees of a MR
+
+| field | value |
+| --- | --- |
+| `key_path` | **`redis_hll_counters.code_review.i_code_review_user_assignees_changed_weekly`** |
+| `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` | [Introduced by](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55486) |
+| `time_frame` | 7d |
+| `data_source` | Redis_hll |
+| `distribution` | ce, ee |
+| `tier` | free, premium, ultimate |
+
 ## `redis_hll_counters.code_review.i_code_review_user_close_mr_monthly`
 
 Count of unique users per week|month who closed a MR
@@ -13692,6 +13732,46 @@ Missing description
 | `tier` |  |
 | `skip_validation` | true |
 
+## `redis_hll_counters.code_review.i_code_review_user_reviewers_changed_monthly`
+
+Count of unique users per month who changed reviewers of a MR
+
+| field | value |
+| --- | --- |
+| `key_path` | **`redis_hll_counters.code_review.i_code_review_user_reviewers_changed_monthly`** |
+| `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` | [Introduced by](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55486) |
+| `time_frame` | 28d |
+| `data_source` | Redis_hll |
+| `distribution` | ce, ee |
+| `tier` | free, premium, ultimate |
+
+## `redis_hll_counters.code_review.i_code_review_user_reviewers_changed_weekly`
+
+Count of unique users per week who changed reviewers of a MR
+
+| field | value |
+| --- | --- |
+| `key_path` | **`redis_hll_counters.code_review.i_code_review_user_reviewers_changed_weekly`** |
+| `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` | [Introduced by](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55486) |
+| `time_frame` | 7d |
+| `data_source` | Redis_hll |
+| `distribution` | ce, ee |
+| `tier` | free, premium, ultimate |
+
 ## `redis_hll_counters.code_review.i_code_review_user_single_file_diffs_monthly`
 
 Count of unique users per week|month with diffs viewed file by file

lib/gitlab/usage_data_counters/aggregated_metrics/code_review.yml

@@ -46,7 +46,9 @@
     'i_code_review_user_mr_discussion_locked',
     'i_code_review_user_mr_discussion_unlocked',
     'i_code_review_user_time_estimate_changed',
-    'i_code_review_user_time_spent_changed'
+    'i_code_review_user_time_spent_changed',
+    'i_code_review_user_assignees_changed',
+    'i_code_review_user_reviewers_changed'
   ]
 - name: code_review_category_monthly_active_users
   operator: OR
@@ -86,7 +88,9 @@
     'i_code_review_user_mr_discussion_locked',
     'i_code_review_user_mr_discussion_unlocked',
     'i_code_review_user_time_estimate_changed',
-    'i_code_review_user_time_spent_changed'
+    'i_code_review_user_time_spent_changed',
+    'i_code_review_user_assignees_changed',
+    'i_code_review_user_reviewers_changed'
   ]
 - name: code_review_extension_category_monthly_active_users
   operator: OR

lib/gitlab/usage_data_counters/known_events/code_review_events.yml

@@ -184,3 +184,13 @@
   category: code_review
   aggregation: weekly
   feature_flag: usage_data_i_code_review_user_time_spent_changed
+- name: i_code_review_user_assignees_changed
+  redis_slot: code_review
+  category: code_review
+  aggregation: weekly
+  feature_flag: usage_data_i_code_review_user_assignees_changed
+- name: i_code_review_user_reviewers_changed
+  redis_slot: code_review
+  category: code_review
+  aggregation: weekly
+  feature_flag: usage_data_i_code_review_user_reviewers_changed

lib/gitlab/usage_data_counters/merge_request_activity_unique_counter.rb

@@ -39,6 +39,8 @@ module Gitlab
       MR_DISCUSSION_UNLOCKED_ACTION = 'i_code_review_user_mr_discussion_unlocked'
       MR_TIME_ESTIMATE_CHANGED_ACTION = 'i_code_review_user_time_estimate_changed'
       MR_TIME_SPENT_CHANGED_ACTION = 'i_code_review_user_time_spent_changed'
+      MR_ASSIGNEES_CHANGED_ACTION = 'i_code_review_user_assignees_changed'
+      MR_REVIEWERS_CHANGED_ACTION = 'i_code_review_user_reviewers_changed'
 
       class << self
         def track_mr_diffs_action(merge_request:)
@@ -173,6 +175,14 @@ module Gitlab
           track_unique_action_by_user(MR_TIME_SPENT_CHANGED_ACTION, user)
         end
 
+        def track_assignees_changed_action(user:)
+          track_unique_action_by_user(MR_ASSIGNEES_CHANGED_ACTION, user)
+        end
+
+        def track_reviewers_changed_action(user:)
+          track_unique_action_by_user(MR_REVIEWERS_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

@@ -316,4 +316,20 @@ RSpec.describe Gitlab::UsageDataCounters::MergeRequestActivityUniqueCounter, :cl
       let(:action) { described_class::MR_TIME_SPENT_CHANGED_ACTION }
     end
   end
+
+  describe '.track_assignees_changed_action' do
+    subject { described_class.track_assignees_changed_action(user: user) }
+
+    it_behaves_like 'a tracked merge request unique event' do
+      let(:action) { described_class::MR_ASSIGNEES_CHANGED_ACTION }
+    end
+  end
+
+  describe '.track_reviewers_changed_action' do
+    subject { described_class.track_reviewers_changed_action(user: user) }
+
+    it_behaves_like 'a tracked merge request unique event' do
+      let(:action) { described_class::MR_REVIEWERS_CHANGED_ACTION }
+    end
+  end
 end

spec/services/merge_requests/update_service_spec.rb

@@ -186,6 +186,54 @@ RSpec.describe MergeRequests::UpdateService, :mailer do
 
           MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
         end
+
+        context 'assignees' do
+          context 'when assignees changed' do
+            it 'tracks assignees changed event' do
+              expect(Gitlab::UsageDataCounters::MergeRequestActivityUniqueCounter)
+                .to receive(:track_assignees_changed_action).once.with(user: user)
+
+              opts[:assignees] = [user2]
+
+              MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
+            end
+          end
+
+          context 'when assignees did not change' do
+            it 'does not track assignees changed event' do
+              expect(Gitlab::UsageDataCounters::MergeRequestActivityUniqueCounter)
+                .not_to receive(:track_assignees_changed_action)
+
+              opts[:assignees] = merge_request.assignees
+
+              MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
+            end
+          end
+        end
+
+        context 'reviewers' do
+          context 'when reviewers changed' do
+            it 'tracks reviewers changed event' do
+              expect(Gitlab::UsageDataCounters::MergeRequestActivityUniqueCounter)
+                .to receive(:track_reviewers_changed_action).once.with(user: user)
+
+              opts[:reviewers] = [user2]
+
+              MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
+            end
+          end
+
+          context 'when reviewers did not change' do
+            it 'does not track reviewers changed event' do
+              expect(Gitlab::UsageDataCounters::MergeRequestActivityUniqueCounter)
+                .not_to receive(:track_reviewers_changed_action)
+
+              opts[:reviewers] = merge_request.reviewers
+
+              MergeRequests::UpdateService.new(project, user, opts).execute(merge_request)
+            end
+          end
+        end
       end
 
       context 'updating milestone' do