Adjust client middleware metrics Counter

According to https://github.com/mperham/sidekiq/wiki/Middleware
the client middleware of Sidekiq can either be a String of the class
name, of the class itself.

At this change we enforce a constantize when a String is given.

lib/gitlab/sidekiq_middleware/client_metrics.rb

@@ -9,8 +9,10 @@ module Gitlab
         @metrics = init_metrics
       end
 
-      def call(worker, _job, queue, _redis_pool)
-        labels = create_labels(worker.class, queue)
+      def call(worker_class, _job, queue, _redis_pool)
+        # worker_class can either be the string or class of the worker being enqueued.
+        worker_class = worker_class.safe_constantize if worker_class.respond_to?(:safe_constantize)
+        labels = create_labels(worker_class, queue)
 
         @metrics.fetch(ENQUEUED).increment(labels, 1)
 

lib/gitlab/sidekiq_middleware/metrics.rb

@@ -10,7 +10,7 @@ module Gitlab
 
       def create_labels(worker_class, queue)
         labels = { queue: queue.to_s, latency_sensitive: FALSE_LABEL, external_dependencies: FALSE_LABEL, feature_category: "", boundary: "" }
-        return labels unless worker_class.include? WorkerAttributes
+        return labels unless worker_class && worker_class.include?(WorkerAttributes)
 
         labels[:latency_sensitive] = bool_as_label(worker_class.latency_sensitive_worker?)
         labels[:external_dependencies] = bool_as_label(worker_class.worker_has_external_dependencies?)

spec/lib/gitlab/sidekiq_middleware/client_metrics_spec.rb

@@ -21,13 +21,19 @@ describe Gitlab::SidekiqMiddleware::ClientMetrics do
 
         describe '#call' do
           it 'yields block' do
-            expect { |b| subject.call(worker, job, :test, double, &b) }.to yield_control.once
+            expect { |b| subject.call(worker_class, job, :test, double, &b) }.to yield_control.once
           end
 
-          it 'increments enqueued jobs metric' do
+          it 'increments enqueued jobs metric with correct labels when worker is a string of the class' do
             expect(enqueued_jobs_metric).to receive(:increment).with(labels, 1)
 
-            subject.call(worker, job, :test, double) { nil }
+            subject.call(worker_class.to_s, job, :test, double) { nil }
+          end
+
+          it 'increments enqueued jobs metric with correct labels' do
+            expect(enqueued_jobs_metric).to receive(:increment).with(labels, 1)
+
+            subject.call(worker_class, job, :test, double) { nil }
           end
         end
       end
@@ -46,7 +52,7 @@ describe Gitlab::SidekiqMiddleware::ClientMetrics do
 
     context "when workers are attributed" do
       def create_attributed_worker_class(latency_sensitive, external_dependencies, resource_boundary, category)
-        Class.new do
+        klass = Class.new do
           include Sidekiq::Worker
           include WorkerAttributes
 
@@ -55,6 +61,7 @@ describe Gitlab::SidekiqMiddleware::ClientMetrics do
           worker_resource_boundary resource_boundary unless resource_boundary == :unknown
           feature_category category unless category.nil?
         end
+        stub_const("TestAttributedWorker", klass)
       end
 
       let(:latency_sensitive) { false }