Do not fail when cleaning up MR with no repository

When we clean up refs of a merge request that is on a project
with no repository anymore, the MergeRequests::CleanupRefsService
will fail.

Before this fix, it'll throw an error and retry and will not set
the cleanup schedule as completed. When the cleanup schedule is
not marked as completed, it'll be picked up by the scheduler
again.

To fix that, we are now checking if the repository exists before
deleting refs. This way, we can still update the cleanup schedule.

app/services/merge_requests/cleanup_refs_service.rb

@@ -31,7 +31,7 @@ module MergeRequests
       return error('Failed to create keep around refs.') unless kept_around?
       return error('Failed to cache merge ref sha.') unless cache_merge_ref_sha
 
-      delete_refs
+      delete_refs if repository.exists?
 
       return error('Failed to update schedule.') unless update_schedule
 

changelogs/unreleased/245263-fix-cleanup-service-no-repository.yml

+---
+title: Do not fail when cleaning up MR with no repository
+merge_request: 47744
+author:
+type: fixed

spec/services/merge_requests/cleanup_refs_service_spec.rb

@@ -115,6 +115,19 @@ RSpec.describe MergeRequests::CleanupRefsService do
 
         it_behaves_like 'service that does not clean up merge request refs'
       end
+
+      context 'when repository no longer exists' do
+        before do
+          Repositories::DestroyService.new(merge_request.project.repository).execute
+        end
+
+        it 'does not fail and still mark schedule as complete' do
+          aggregate_failures do
+            expect(result[:status]).to eq(:success)
+            expect(merge_request.cleanup_schedule.completed_at).to be_present
+          end
+        end
+      end
     end
 
     shared_examples_for 'service that does not clean up merge request refs' do