Ensure pool participants are linked before GC

In theory the case could happen that the initial linking of the pool
fails and so do all the retries that Sidekiq performs. This could lead
to data loss.

To prevent that case, linking is done before Gits GC too. This makes
sure that case doesn't happen.

app/models/project.rb

@@ -2039,6 +2039,10 @@ class Project < ActiveRecord::Base
     pool_repository&.unlink_repository(repository) && update_column(:pool_repository_id, nil)
   end
 
+  def link_pool_repository
+    pool_repository&.link_repository(repository)
+  end
+
   private
 
   def merge_requests_allowing_collaboration(source_branch = nil)

app/workers/git_garbage_collect_worker.rb

@@ -23,6 +23,7 @@ class GitGarbageCollectWorker
     end
 
     task = task.to_sym
+    project.link_pool_repository
     gitaly_call(task, project.repository.raw_repository)
 
     # Refresh the branch cache in case garbage collection caused a ref lookup to fail

app/workers/object_pool/join_worker.rb

@@ -5,14 +5,13 @@ module ObjectPool
     include ApplicationWorker
     include ObjectPoolQueue
 
-    def perform(pool_id, project_id)
-      pool = PoolRepository.find_by_id(pool_id)
-      return unless pool&.joinable?
-
+    # The use of pool id is deprecated. Keeping the argument allows old jobs to
+    # still be performed.
+    def perform(_pool_id, project_id)
       project = Project.find_by_id(project_id)
-      return unless project
+      return unless project&.pool_repository&.joinable?
 
-      pool.link_repository(project.repository)
+      project.link_pool_repository
 
       Projects::HousekeepingService.new(project).execute
     end

spec/workers/git_garbage_collect_worker_spec.rb

@@ -71,6 +71,17 @@ describe GitGarbageCollectWorker do
 
           subject.perform(project.id)
         end
+
+        context 'when the repository has joined a pool' do
+          let!(:pool) { create(:pool_repository, :ready) }
+          let(:project) { pool.source_project }
+
+          it 'ensures the repositories are linked' do
+            expect_any_instance_of(PoolRepository).to receive(:link_repository).once
+
+            subject.perform(project.id)
+          end
+        end
       end
 
       context 'when no lease can be obtained' do