Merge branch '273131-fix-mr-create-push-option-race' into 'master'

Fix intermittent 'branch not found' errors when pushing creates an MR

See merge request gitlab-org/gitlab!68362

app/services/merge_requests/push_options_handler_service.rb

@@ -65,7 +65,7 @@ module MergeRequests
       end
 
       if push_options[:target] && !target_project.repository.branch_exists?(push_options[:target])
-        errors << "Branch #{push_options[:target]} does not exist"
+        errors << "Target branch #{target_project.full_path}:#{push_options[:target]} does not exist"
       end
     end
 

app/services/post_receive_service.rb

@@ -17,13 +17,18 @@ class PostReceiveService
     response = Gitlab::InternalPostReceive::Response.new
 
     push_options = Gitlab::PushOptions.new(params[:push_options])
+    mr_options = push_options.get(:merge_request)
 
     response.reference_counter_decreased = Gitlab::ReferenceCounter.new(params[:gl_repository]).decrease
 
+    # The PostReceive worker will normally invalidate the cache. However, it
+    # runs asynchronously. If push options require us to create a new merge
+    # request synchronously, we can't rely on that, so invalidate the cache here
+    repository&.expire_branches_cache if mr_options&.fetch(:create, false)
+
     PostReceive.perform_async(params[:gl_repository], params[:identifier],
                               params[:changes], push_options.as_json)
 
-    mr_options = push_options.get(:merge_request)
     if mr_options.present?
       message = process_mr_push_options(mr_options, params[:changes])
       response.add_alert_message(message)

qa/qa/specs/features/api/3_create/merge_request/push_options_target_branch_spec.rb

@@ -25,18 +25,6 @@ module QA
           push.file_content = "Target branch test target branch #{SecureRandom.hex(8)}"
         end
 
-        # Confirm the target branch can be checked out to avoid a race condition
-        # where the subsequent push option attempts to create an MR before the target branch is ready.
-        Support::Retrier.retry_on_exception(sleep_interval: 5) do
-          Git::Repository.perform do |repository|
-            repository.uri = project.repository_http_location.uri
-            repository.use_default_credentials
-            repository.clone
-            repository.configure_identity('GitLab QA', 'root@gitlab.com')
-            repository.checkout(target_branch)
-          end
-        end
-
         Resource::Repository::ProjectPush.fabricate! do |push|
           push.project = project
           push.branch_name = "push-options-test-#{SecureRandom.hex(8)}"

spec/services/merge_requests/push_options_handler_service_spec.rb

@@ -743,7 +743,7 @@ RSpec.describe MergeRequests::PushOptionsHandlerService do
     it 'records an error' do
       service.execute
 
-      expect(service.errors).to eq(['Branch my-branch does not exist'])
+      expect(service.errors).to eq(["Target branch #{project.full_path}:my-branch does not exist"])
     end
   end
 

spec/services/post_receive_service_spec.rb

@@ -131,6 +131,12 @@ RSpec.describe PostReceiveService do
         project.add_developer(user)
       end
 
+      it 'invalidates the branch name cache' do
+        expect(service.repository).to receive(:expire_branches_cache).and_call_original
+
+        subject
+      end
+
       it 'invokes MergeRequests::PushOptionsHandlerService' do
         expect(MergeRequests::PushOptionsHandlerService).to receive(:new).and_call_original