Log top-level relation creationg when Importing Project/Group

- This MR adds a log entry for each top-level relation creation
  during Group/Project Import, when importing to a group that has
  `log_import_export_relation_creation` feature flag enabled
- It's behind a feature flag and only for groups in order to not
  produce too many log entries that are not particularly useful
  most of the cases, however they can be during ProServ team
  customers migrations from self-managed to GitLab.com

lib/gitlab/import_export/relation_tree_restorer.rb

@@ -71,6 +71,7 @@ module Gitlab
 
         import_failure_service.with_retry(action: 'relation_object.save!', relation_key: relation_key, relation_index: relation_index) do
           relation_object.save!
+          log_relation_creation(@importable, relation_key, relation_object)
         end
       rescue => e
         import_failure_service.log_import_failure(
@@ -218,6 +219,25 @@ module Gitlab
 
         relation_reader.sort_ci_pipelines_by_id
       end
+
+      # Enable logging of each top-level relation creation when Importing
+      # into a Group if feature flag is enabled
+      def log_relation_creation(importable, relation_key, relation_object)
+        root_ancestor_group = importable.try(:root_ancestor)
+
+        return unless root_ancestor_group
+        return unless root_ancestor_group.instance_of?(::Group)
+        return unless Feature.enabled?(:log_import_export_relation_creation, root_ancestor_group)
+
+        @shared.logger.info(
+          importable_type: importable.class.to_s,
+          importable_id: importable.id,
+          relation_key: relation_key,
+          relation_id: relation_object.id,
+          author_id: relation_object.try(:author_id),
+          message: '[Project/Group Import] Created new object relation'
+        )
+      end
     end
   end
 end

spec/lib/gitlab/import_export/relation_tree_restorer_spec.rb

@@ -60,6 +60,38 @@ describe Gitlab::ImportExport::RelationTreeRestorer do
     end
   end
 
+  shared_examples 'logging of relations creation' do
+    context 'when log_import_export_relation_creation feature flag is enabled' do
+      before do
+        stub_feature_flags(log_import_export_relation_creation: { enabled: true, thing: group })
+      end
+
+      it 'logs top-level relation creation' do
+        expect(relation_tree_restorer.shared.logger)
+          .to receive(:info)
+          .with(hash_including(message: '[Project/Group Import] Created new object relation'))
+          .at_least(:once)
+
+        subject
+      end
+    end
+
+    context 'when log_import_export_relation_creation feature flag is disabled' do
+      before do
+        stub_feature_flags(log_import_export_relation_creation: { enabled: false, thing: group })
+      end
+
+      it 'does not log top-level relation creation' do
+        expect(relation_tree_restorer.shared.logger)
+          .to receive(:info)
+          .with(hash_including(message: '[Project/Group Import] Created new object relation'))
+          .never
+
+        subject
+      end
+    end
+  end
+
   context 'when restoring a project' do
     let(:path) { 'spec/fixtures/lib/gitlab/import_export/complex/project.json' }
     let(:importable) { create(:project, :builds_enabled, :issues_disabled, name: 'project', path: 'project') }
@@ -71,6 +103,30 @@ describe Gitlab::ImportExport::RelationTreeRestorer do
       let(:relation_reader) { Gitlab::ImportExport::JSON::LegacyReader::File.new(path, reader.project_relation_names) }
 
       it_behaves_like 'import project successfully'
+
+      context 'logging of relations creation' do
+        let(:group) { create(:group) }
+        let(:importable) { create(:project, :builds_enabled, :issues_disabled, name: 'project', path: 'project', group: group) }
+
+        include_examples 'logging of relations creation'
+      end
+    end
+  end
+
+  context 'when restoring a group' do
+    let(:path) { 'spec/fixtures/lib/gitlab/import_export/group_exports/no_children/group.json' }
+    let(:group) { create(:group) }
+    let(:importable) { create(:group, parent: group) }
+    let(:object_builder) { Gitlab::ImportExport::Group::ObjectBuilder }
+    let(:relation_factory) { Gitlab::ImportExport::Group::RelationFactory }
+    let(:relation_reader) { Gitlab::ImportExport::JSON::LegacyReader::File.new(path, reader.group_relation_names) }
+    let(:reader) do
+      Gitlab::ImportExport::Reader.new(
+        shared: shared,
+        config: Gitlab::ImportExport::Config.new(config: Gitlab::ImportExport.group_config_file).to_h
+      )
     end
+
+    include_examples 'logging of relations creation'
   end
 end

spec/services/groups/import_export/import_service_spec.rb

@@ -15,6 +15,10 @@ describe Groups::ImportExport::ImportService do
 
     before do
       ImportExportUpload.create(group: group, import_file: import_file)
+
+      allow(Gitlab::Import::Logger).to receive(:build).and_return(import_logger)
+      allow(import_logger).to receive(:error)
+      allow(import_logger).to receive(:info)
     end
 
     context 'when user has correct permissions' do
@@ -29,13 +33,11 @@ describe Groups::ImportExport::ImportService do
       end
 
       it 'logs the import success' do
-        allow(Gitlab::Import::Logger).to receive(:build).and_return(import_logger)
-
         expect(import_logger).to receive(:info).with(
           group_id:   group.id,
           group_name: group.name,
           message:    'Group Import/Export: Import succeeded'
-        )
+        ).once
 
         subject
       end
@@ -45,8 +47,6 @@ describe Groups::ImportExport::ImportService do
       let(:user) { create(:user) }
 
       it 'logs the error and raises an exception' do
-        allow(Gitlab::Import::Logger).to receive(:build).and_return(import_logger)
-
         expect(import_logger).to receive(:error).with(
           group_id:   group.id,
           group_name: group.name,
@@ -71,16 +71,12 @@ describe Groups::ImportExport::ImportService do
     context 'when there are errors with the import file' do
       let(:import_file) { fixture_file_upload('spec/fixtures/symlink_export.tar.gz') }
 
-      before do
-        allow(Gitlab::Import::Logger).to receive(:build).and_return(import_logger)
-      end
-
       it 'logs the error and raises an exception' do
         expect(import_logger).to receive(:error).with(
           group_id:   group.id,
           group_name: group.name,
           message:    a_string_including('Errors occurred')
-        )
+        ).once
 
         expect { subject }.to raise_error(Gitlab::ImportExport::Error)
       end