Avoid race condition when expiring artifacts

It may happen that job meant to remove expired artifacts will be
executed asynchronously when, in the meantime, project associated with
given build gets removed by another asynchronous job. In that case we
should not remove artifacts because such build will be removed anyway,
when project removal is complete.

app/workers/expire_build_instance_artifacts_worker.rb

@@ -2,10 +2,14 @@ class ExpireBuildInstanceArtifactsWorker
   include Sidekiq::Worker
 
   def perform(build_id)
-    build = Ci::Build.with_expired_artifacts.reorder(nil).find_by(id: build_id)
-    return unless build
+    build = Ci::Build
+      .with_expired_artifacts
+      .reorder(nil)
+      .find_by(id: build_id)
 
-    Rails.logger.info "Removing artifacts build #{build.id}..."
+    return unless build.try(:project)
+
+    Rails.logger.info "Removing artifacts for build #{build.id}..."
     build.erase_artifacts!
   end
 end

spec/workers/expire_build_instance_artifacts_worker_spec.rb

@@ -6,28 +6,48 @@ describe ExpireBuildInstanceArtifactsWorker do
   let(:worker) { described_class.new }
 
   describe '#perform' do
-    before { build }
-
-    subject! { worker.perform(build.id) }
+    before do
+      worker.perform(build.id)
+    end
 
     context 'with expired artifacts' do
-      let(:build) { create(:ci_build, :artifacts, artifacts_expire_at: Time.now - 7.days) }
+      let(:artifacts_expiry) { { artifacts_expire_at: Time.now - 7.days } }
 
-      it 'does expire' do
-        expect(build.reload.artifacts_expired?).to be_truthy
+      context 'when associated project is valid' do
+        let(:build) do
+          create(:ci_build, :artifacts, artifacts_expiry)
+        end
+
+        it 'does expire' do
+          expect(build.reload.artifacts_expired?).to be_truthy
+        end
+
+        it 'does remove files' do
+          expect(build.reload.artifacts_file.exists?).to be_falsey
+        end
+
+        it 'does nullify artifacts_file column' do
+          expect(build.reload.artifacts_file_identifier).to be_nil
+        end
       end
 
-      it 'does remove files' do
-        expect(build.reload.artifacts_file.exists?).to be_falsey
-      end
+      context 'when associated project was removed' do
+        let(:build) do
+          create(:ci_build, :artifacts, artifacts_expiry) do |build|
+            build.project.delete
+          end
+        end
 
-      it 'does nullify artifacts_file column' do
-        expect(build.reload.artifacts_file_identifier).to be_nil
+        it 'does not remove artifacts' do
+          expect(build.reload.artifacts_file.exists?).to be_truthy
+        end
       end
     end
 
     context 'with not yet expired artifacts' do
-      let(:build) { create(:ci_build, :artifacts, artifacts_expire_at: Time.now + 7.days) }
+      let(:build) do
+        create(:ci_build, :artifacts, artifacts_expire_at: Time.now + 7.days)
+      end
 
       it 'does not expire' do
         expect(build.reload.artifacts_expired?).to be_falsey