Start merge request for custom dashboard if new branch is provided

app/services/metrics/dashboard/update_dashboard_service.rb

@@ -12,7 +12,8 @@ module Metrics
       steps :check_push_authorized,
         :check_branch_name,
         :check_file_type,
-        :update_file
+        :update_file,
+        :create_merge_request
 
       def execute
         execute_steps
@@ -49,6 +50,23 @@ module Metrics
         end
       end
 
+      def create_merge_request(result)
+        return success(result) if project.default_branch == branch
+
+        merge_request_params = {
+          source_branch: branch,
+          target_branch: project.default_branch,
+          title: params[:commit_message]
+        }
+        merge_request = ::MergeRequests::CreateService.new(project, current_user, merge_request_params).execute
+
+        if merge_request.persisted?
+          success(result.merge(merge_request: Gitlab::UrlBuilder.build(merge_request)))
+        else
+          error(merge_request.errors.full_messages.join(','), :bad_request)
+        end
+      end
+
       def push_authorized?
         Gitlab::UserAccess.new(current_user, project: project).can_push_to_branch?(branch)
       end

changelogs/unreleased/208174-create-merge-request.yml

+---
+title: Start merge request for custom dashboard if new branch is provided
+merge_request: 27189
+author:
+type: added

spec/services/metrics/dashboard/update_dashboard_service_spec.rb

@@ -92,6 +92,8 @@ describe Metrics::Dashboard::UpdateDashboardService, :use_clean_rails_memory_sto
       end
 
       context 'Files::UpdateService success' do
+        let(:merge_request) { project.merge_requests.last }
+
         before do
           allow(::Files::UpdateService).to receive(:new).and_return(double(execute: { status: :success }))
         end
@@ -107,6 +109,31 @@ describe Metrics::Dashboard::UpdateDashboardService, :use_clean_rails_memory_sto
           expect(service_call[:status]).to be :success
           expect(service_call[:http_status]).to be :created
           expect(service_call[:dashboard]).to match dashboard_details
+          expect(service_call[:merge_request]).to eq(Gitlab::UrlBuilder.build(merge_request))
+        end
+
+        context 'when the merge request does not succeed' do
+          let(:error_message) { 'There was an error' }
+
+          let(:merge_request) do
+            build(:merge_request, target_project: project, source_project: project, author: user)
+          end
+
+          before do
+            merge_request.errors.add(:base, error_message)
+            allow_next_instance_of(::MergeRequests::CreateService) do |mr|
+              allow(mr).to receive(:execute).and_return(merge_request)
+            end
+          end
+
+          it 'returns an appropriate message and status code', :aggregate_failures do
+            result = service_call
+
+            expect(result.keys).to contain_exactly(:message, :http_status, :status, :last_step)
+            expect(result[:status]).to eq(:error)
+            expect(result[:http_status]).to eq(:bad_request)
+            expect(result[:message]).to eq(error_message)
+          end
         end
 
         context 'with escaped characters in file name' do
@@ -125,6 +152,25 @@ describe Metrics::Dashboard::UpdateDashboardService, :use_clean_rails_memory_sto
             expect(service_call[:dashboard]).to match dashboard_details
           end
         end
+
+        context 'when pushing to the default branch' do
+          let(:branch) { 'master' }
+
+          it 'does not create a merge request', :aggregate_failures do
+            dashboard_details = {
+              path: '.gitlab/dashboards/custom_dashboard.yml',
+              display_name: 'custom_dashboard.yml',
+              default: false,
+              system_dashboard: false
+            }
+
+            expect(::MergeRequests::CreateService).not_to receive(:new)
+            expect(service_call.keys).to contain_exactly(:dashboard, :http_status, :status)
+            expect(service_call[:status]).to be :success
+            expect(service_call[:http_status]).to be :created
+            expect(service_call[:dashboard]).to match dashboard_details
+          end
+        end
       end
 
       context 'Files::UpdateService fails' do