Add a Dangerbot rule to suggest adding specs for Redis/HLL metrics migration

danger/analytics_instrumentation/Dangerfile

@@ -11,3 +11,5 @@ analytics_instrumentation.check_usage_data_insertions!
 analytics_instrumentation.check_deprecated_data_sources!
 
 analytics_instrumentation.check_removed_metric_fields!
+
+analytics_instrumentation.warn_about_migrated_redis_keys_specs!

spec/tooling/danger/analytics_instrumentation_spec.rb

@@ -443,4 +443,38 @@
       end
     end
   end
+
+  describe '#warn_about_migrated_redis_keys_specs!' do
+    let(:redis_hll_file) { 'lib/gitlab/usage_data_counters/hll_redis_key_overrides.yml' }
+    let(:total_counter_file) { 'lib/gitlab/usage_data_counters/total_counter_redis_key_overrides.yml' }
+
+    subject(:check_redis_keys_files_overrides) { analytics_instrumentation.warn_about_migrated_redis_keys_specs! }
+
+    before do
+      allow(fake_helper).to receive(:changed_lines).with(redis_hll_file).and_return([file_diff_hll])
+      allow(fake_helper).to receive(:changed_lines).with(total_counter_file).and_return([file_diff_total])
+    end
+
+    context 'when new keys added to overrides files' do
+      let(:file_diff_hll) { "+user_viewed_cluster_configuration-user: user_viewed_cluster_configuration" }
+      let(:file_diff_total) { "+user_viewed_cluster_configuration-user: USER_VIEWED_CLUSTER_CONFIGURATION" }
+
+      it 'adds suggestion to add specs' do
+        expect(analytics_instrumentation).to receive(:warn)
+
+        check_redis_keys_files_overrides
+      end
+    end
+
+    context 'when no new keys added to overrides files' do
+      let(:file_diff_hll) { "-user_viewed_cluster_configuration-user: user_viewed_cluster_configuration" }
+      let(:file_diff_total) { "-user_viewed_cluster_configuration-user: USER_VIEWED_CLUSTER_CONFIGURATION" }
+
+      it 'adds suggestion to add specs' do
+        expect(analytics_instrumentation).not_to receive(:warn)
+
+        check_redis_keys_files_overrides
+      end
+    end
+  end
 end

tooling/danger/analytics_instrumentation.rb

@@ -97,12 +97,22 @@ def check_removed_metric_fields!
         end
       end
 
-      def modified_config_files
-        helper.modified_files.select { |f| f.include?('config/metrics') && f.end_with?('yml') }
+      def warn_about_migrated_redis_keys_specs!
+        override_files_changes = ["lib/gitlab/usage_data_counters/hll_redis_key_overrides.yml",
+          "lib/gitlab/usage_data_counters/total_counter_redis_key_overrides.yml"].map do |filename|
+          helper.changed_lines(filename).filter { |line| line.start_with?("+") }
+        end
+        return if override_files_changes.flatten.none?
+
+        warn "Redis keys overrides were added. Please consider cover keys merging with specs. See the [related issue](https://gitlab.com/gitlab-org/gitlab/-/issues/475191) for details"
       end
 
       private
 
+      def modified_config_files
+        helper.modified_files.select { |f| f.include?('config/metrics') && f.end_with?('yml') }
+      end
+
       def comment_removed_metric(filename, has_removed_url, has_removed_milestone)
         mr_has_milestone = !helper.mr_milestone.nil?
         milestone = mr_has_milestone ? helper.mr_milestone['title'] : '[PLEASE SET MILESTONE]'