Fix mail worker error in versioning middleware

Only assign version for ApplicationWorker

config/feature_flags/development/sidekiq_versioning.yml

+---
+name: sidekiq_versioning
+introduced_by_url: 
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/232934
+group: group::fulfillment
+type: development
+default_enabled: false
\ No newline at end of file

lib/gitlab/sidekiq_middleware.rb

@@ -19,6 +19,7 @@ module Gitlab
         chain.add ::Labkit::Middleware::Sidekiq::Server
         chain.add ::Gitlab::SidekiqMiddleware::InstrumentationLogger
         chain.add ::Gitlab::SidekiqMiddleware::AdminMode::Server
+        chain.add ::Gitlab::SidekiqVersioning::Middleware
         chain.add ::Gitlab::SidekiqStatus::ServerMiddleware
         chain.add ::Gitlab::SidekiqMiddleware::WorkerContext::Server
         chain.add ::Gitlab::SidekiqMiddleware::DuplicateJobs::Server

lib/gitlab/sidekiq_versioning.rb

@@ -5,10 +5,6 @@ module Gitlab
     def self.install!
       Sidekiq::Manager.prepend SidekiqVersioning::Manager
 
-      Sidekiq.server_middleware do |chain|
-        chain.add SidekiqVersioning::Middleware
-      end
-
       # The Sidekiq client API always adds the queue to the Sidekiq queue
       # list, but mail_room and gitlab-shell do not. This is only necessary
       # for monitoring.

lib/gitlab/sidekiq_versioning/middleware.rb

@@ -4,7 +4,7 @@ module Gitlab
   module SidekiqVersioning
     class Middleware
       def call(worker, job, queue)
-        worker.job_version = job['version']
+        worker.job_version = job['version'] if worker.is_a?(ApplicationWorker) && Feature.enabled?(:sidekiq_versioning)
 
         yield
       end

spec/lib/gitlab/sidekiq_middleware_spec.rb

@@ -51,6 +51,7 @@ RSpec.describe Gitlab::SidekiqMiddleware do
        Gitlab::SidekiqMiddleware::BatchLoader,
        Labkit::Middleware::Sidekiq::Server,
        Gitlab::SidekiqMiddleware::InstrumentationLogger,
+       Gitlab::SidekiqVersioning::Middleware,
        Gitlab::SidekiqStatus::ServerMiddleware,
        Gitlab::SidekiqMiddleware::ServerMetrics,
        Gitlab::SidekiqMiddleware::ArgumentsLogger,
@@ -78,6 +79,41 @@ RSpec.describe Gitlab::SidekiqMiddleware do
       end
     end
 
+    shared_examples "a server middleware chain for mailer" do
+      let(:worker_class) { ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper }
+      let(:job_args) do
+        [
+          {
+            "job_class" => "ActionMailer::MailDeliveryJob",
+            "job_id" => "a180b47c-3fd6-41b8-81e9-34da61c3400e",
+            "provider_job_id" => nil,
+            "queue_name" => "mailers",
+            "priority" => nil,
+            "arguments" => [
+              "Notify",
+              "test_email",
+              "deliver_now",
+              {
+                "args" => [
+                  "test@example.com",
+                  "subject",
+                  "body"
+                ],
+                "_aj_symbol_keys" => ["args"]
+              }
+            ],
+            "executions" => 0,
+            "exception_executions" => {},
+            "locale" => "en",
+            "timezone" => "UTC",
+            "enqueued_at" => "2020-07-27T07:43:31Z"
+          }
+        ]
+      end
+
+      it_behaves_like "a server middleware chain"
+    end
+
     context "all optional middlewares off" do
       let(:metrics) { false }
       let(:arguments_logger) { false }
@@ -91,6 +127,7 @@ RSpec.describe Gitlab::SidekiqMiddleware do
       end
 
       it_behaves_like "a server middleware chain"
+      it_behaves_like "a server middleware chain for mailer"
     end
 
     context "all optional middlewares on" do
@@ -100,6 +137,7 @@ RSpec.describe Gitlab::SidekiqMiddleware do
       let(:disabled_sidekiq_middlewares) { [] }
 
       it_behaves_like "a server middleware chain"
+      it_behaves_like "a server middleware chain for mailer"
 
       context "server metrics" do
         let(:gitaly_histogram) { double(:gitaly_histogram) }

spec/lib/gitlab/sidekiq_versioning/middleware_spec.rb

@@ -34,5 +34,27 @@ RSpec.describe Gitlab::SidekiqVersioning::Middleware do
     it 'yields' do
       expect { |b| call!(&b) }.to yield_control
     end
+
+    context 'when worker is not ApplicationWorker' do
+      let(:worker_class) do
+        ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper
+      end
+
+      it 'does not err' do
+        expect { call! }.not_to raise_error
+      end
+    end
+
+    context 'when sidekiq_versioning is disabled' do
+      before do
+        stub_feature_flags(sidekiq_versioning: false)
+      end
+
+      it 'does not set job_version' do
+        expect(worker).not_to receive(:job_version=)
+
+        call!
+      end
+    end
   end
 end

spec/lib/gitlab/sidekiq_versioning_spec.rb

@@ -35,12 +35,6 @@ RSpec.describe Gitlab::SidekiqVersioning, :redis do
       expect(Sidekiq::Manager).to include(Gitlab::SidekiqVersioning::Manager)
     end
 
-    it 'adds the SidekiqVersioning::Middleware Sidekiq server middleware' do
-      described_class.install!
-
-      expect(Sidekiq.server_middleware.entries.map(&:klass)).to include(Gitlab::SidekiqVersioning::Middleware)
-    end
-
     it 'registers all versionless and versioned queues with Redis' do
       described_class.install!