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

@@ -6,12 +6,17 @@ 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 } }
+
+      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
@@ -26,8 +31,23 @@ describe ExpireBuildInstanceArtifactsWorker do
         end
       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 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