Recreates missing group labels when moving project to another group

app/services/labels/transfer_service.rb

+# Labels::TransferService class
+#
+# User for recreate the missing group labels at project level
+#
+module Labels
+  class TransferService
+    def initialize(current_user, group, project)
+      @current_user = current_user
+      @group = group
+      @project = project
+    end
+
+    def execute
+      return unless group.present?
+
+      Label.transaction do
+        labels_to_transfer = Label.where(id: label_links.select(:label_id).uniq)
+
+        labels_to_transfer.find_each do |label|
+          new_label_id = find_or_create_label!(label)
+
+          LabelLink.where(label_id: label.id).update_all(label_id: new_label_id)
+        end
+      end
+    end
+
+    private
+
+    attr_reader :current_user, :group, :project
+
+    def label_links
+      label_link_ids = []
+      label_link_ids << LabelLink.where(target: project.issues, label: group.labels).select(:id)
+      label_link_ids << LabelLink.where(target: project.merge_requests, label: group.labels).select(:id)
+
+      union = Gitlab::SQL::Union.new(label_link_ids)
+
+      LabelLink.where("label_links.id IN (#{union.to_sql})")
+    end
+
+    def labels
+      @labels ||= LabelsFinder.new(current_user, project_id: project.id).execute
+    end
+
+    def find_or_create_label!(label)
+      new_label = labels.find_by(title: label.title)
+      new_label ||= project.labels.create!(label.attributes.slice("title", "description", "color"))
+
+      new_label.id
+    end
+  end
+end

app/services/projects/transfer_service.rb

@@ -28,6 +28,7 @@ module Projects
       Project.transaction do
         old_path = project.path_with_namespace
         old_namespace = project.namespace
+        old_group = project.group
         new_path = File.join(new_namespace.try(:path) || '', project.path)
         if Project.where(path: project.path, namespace_id: new_namespace.try(:id)).present?
@@ -57,6 +58,9 @@ module Projects
         # Move wiki repo also if present
         gitlab_shell.mv_repository(project.repository_storage_path, "#{old_path}.wiki", "#{new_path}.wiki")
+        # Move missing group labels to project
+        Labels::TransferService.new(current_user, old_group, project).execute
+
         # clear project cached events
         project.reset_events_cache

spec/factories/merge_requests.rb

@@ -68,5 +68,15 @@ FactoryGirl.define do
     factory :closed_merge_request, traits: [:closed]
     factory :reopened_merge_request, traits: [:reopened]
     factory :merge_request_with_diffs, traits: [:with_diffs]
+
+    factory :labeled_merge_request do
+      transient do
+        labels []
+      end
+
+      after(:create) do |merge_request, evaluator|
+        merge_request.update_attributes(labels: evaluator.labels)
+      end
+    end
   end
 end

spec/services/labels/transfer_service_spec.rb

+require 'spec_helper'
+
+describe Labels::TransferService, services: true do
+  describe '#execute' do
+    let(:user)    { create(:user) }
+    let(:group_1) { create(:group) }
+    let(:group_2) { create(:group) }
+    let(:project) { create(:project, namespace: group_2) }
+
+    let(:group_label_1) { create(:group_label, group: group_1, name: 'Group Label 1') }
+    let(:group_label_2) { create(:group_label, group: group_1, name: 'Group Label 2') }
+    let(:group_label_3) { create(:group_label, group: group_1, name: 'Group Label 3') }
+    let(:group_label_4) { create(:group_label, group: group_2, name: 'Group Label 4') }
+    let(:project_label_1) { create(:label, project: project, name: 'Project Label 1') }
+
+    subject(:service) { described_class.new(user, group_1, project) }
+
+    before do
+      create(:labeled_issue, project: project, labels: [group_label_1])
+      create(:labeled_issue, project: project, labels: [group_label_4])
+      create(:labeled_issue, project: project, labels: [project_label_1])
+      create(:labeled_merge_request, source_project: project, labels: [group_label_1, group_label_2])
+    end
+
+    it 'recreates the missing group labels at project level' do
+      expect { service.execute }.to change(project.labels, :count).by(2)
+    end
+
+    it 'does not recreate missing group labels that are not applied to issues or merge requests' do
+      service.execute
+
+      expect(project.labels.where(title: group_label_3.title)).to be_empty
+    end
+
+    it 'does not recreate missing group labels that already exist in the project group' do
+      service.execute
+
+      expect(project.labels.where(title: group_label_4.title)).to be_empty
+    end
+  end
+end

spec/services/projects/transfer_service_spec.rb

@@ -71,4 +71,14 @@ describe Projects::TransferService, services: true do
       it { expect(private_project.visibility_level).to eq(Gitlab::VisibilityLevel::PRIVATE) }
     end
   end
+
+  context 'missing group labels applied to issues or merge requests' do
+    it 'delegates tranfer to Labels::TransferService' do
+      group.add_owner(user)
+
+      expect_any_instance_of(Labels::TransferService).to receive(:execute).once.and_call_original
+
+      transfer_project(project, user, group)
+    end
+  end
 end